---
name: "rksh"
section: "1"
platform: "linux"
package: "pdksh"
version: "5.2.3-6"
release: "Debian 1.1 (Buzz)"
platforms: ["linux"]
url: "https://new.carta.tech/ksh"
---

# rksh(1)

Public domain Korn shell

Part of [ksh(1)](/ksh/1.md).

## NAME

ksh - Public domain Korn shell

## SYNOPSIS

**ksh** \[**±abCefhikmnprsuvxX**\] \[**±o** *option*\] \[ \[ **-c** *command-string* \[*command-name*\] \| **-s** \| *file* \] \[*argument* ...\] \]

## DESCRIPTION

**ksh** is a command interpreter that is intended for both  interactive and shell script use.  Its command language is a superset of the [*sh*(1)](/sh/1.md) shell language.

### Shell Startup

The following options can be specified only on the command line:

- **-c** *command-string*

  the shell executes the command(s) contained in *command-string*

- **-i**

  interactive mode — see below

- **-l**

  login shell — see below interactive mode — see below

- **-s**

  the shell reads commands from standard input; all non-option arguments are positional parameters

- **-r**

  restricted mode — see below

In addition to the above, the options described in the **set** built-in command can also be used on the command line.

If neither the **-c** nor the **-s** options are specified, the first non-option argument specifies the name of a file the shell reads commands from; if there are no non-option arguments, the shell reads commands from standard input. The name of the shell (i.e., the contents of the **$0**) parameter is determined as follows: if the **-c** option is used and there is a non-option argument, it is used as the name; if commands are being read from a file, the file is used as the name; otherwise the name the shell was called with (i.e., argv\[0\]) is used.

A shell is *interactive* if the **-i** option is used or if both standard input and standard error are attached to a tty. An interactive shell has job control enabled (if available), ignores the INT, QUIT and TERM signals, and prints prompts before reading input (see **PS1** and **PS2** parameters). For non-interactive shells, the **trackall** option is on by default (see **set** command below).

A shell is **restricted** if the **-r** option is used or if either the basename of the name the shell is invoked with or the **SHELL** parameter match the pattern \*r\*sh (e.g., rsh, rksh, rpdksh, etc.). The following restrictions come into effect after the shell processes any profile and **$ENV** files:

- •

  the **cd** command is disabled

- •

  the **SHELL**, **ENV** and **PATH** parameters can't be changed

- •

  command names can't be specified with absolute or relative paths

- •

  the **-p** option of the **command** built-in can't be used

- •

  redirections that create files can't be used (i.e., **\>**, **\>\|**, **\>\>**, **\<\>**)

A shell is **privileged** if the **-p** option is used or if the real user-id or group-id does not match the effective user-id or group-id (see [*getuid*(2)](/getuid/2.md), [*getgid*(2)](/getgid/2.md)). A privileged shell does not process $HOME/.profile nor the **ENV** parameter (see below), instead the file /etc/suid\_profile is processed. Clearing the privileged option causes the shell to set its effective user-id (group-id) to its real user-id (group-id).

If the basename of the name the shell is called with (i.e., argv\[0\]) starts with **-** or if the **-l** option is used, the shell is assumed to be a login shell and the shell reads and executes the contents of **/etc/profile** and **$HOME/.profile** if they exist and are readable.

If the **ENV** parameter is set when the shell starts (or, in the case of login shells, after any profiles are processed), its value is subjected to parameter, command, arithmetic and tilde substitution and the resulting file (if any) is read and executed. If **ENV** parameter is not set (and not null) and pdksh was compiled with the **DEFAULT\_ENV** macro defined, the file named in that macro is included (after the above mentioned substitutions have been performed).

The exit status of the shell is 127 if the command file specified on the command line could not be opened, or non-zero if a fatal syntax error occurred during the execution of a script. In the absence of fatal errors, the exit status is that of the last command executed, or zero, if no command is executed.

### Command Syntax

The shell begins parsing its input by breaking it into *word*s. Words, which are sequences of characters, are delimited by unquoted *white-space* characters (space, tab and newline) or *meta-characters* (**\<**, **\>**, **\|**, **;**, **&**, **(** and **)**). Aside from delimiting words, spaces and tabs are ignored, while newlines usually delimit commands. The meta-characters are used in building the following tokens: **\<**, **\<&**, **\<\<**, **\>**, **\>&**, **\>\>**, etc. used to specify redirections (see Input/Output Redirection below); **\|** used to create pipelines; **\|&** used to create co-processes (see Co-Processes below); **;** used to separate commands; **&** used to create asynchronous pipelines; **&&** and **\|\|** used to specify conditional execution; **;;** used in **case** statements; **(** .. **)** used to start subshells; and lastly, **((** .. **))** which are used in arithmetic expressions;

White-space and meta-characters can be quoted individually using backslash (**\\**), or in groups using double (**"**) or single (**'**) quotes. Note that the following characters are also treated specially by the shell and must be quoted if they are to represent themselves: **\\**, **"**, **'**, **#**, **$**, **\`**, **~**, **{**, **}**, **\***, **?** and **\[**. The first three of these are the above mentioned quoting characters (see Quoting below); **#**, if used at the beginning of a word, introduces a comment — everything after the **#** up to the nearest newline is ignored; **$** is used to introduce parameter, command and arithmetic substitutions (see Substitution below); **\`** introduces an old-style command substitution (see Substitution below); **~** begins a directory expansion (see Tilde Expansion below); **{** and **}** delimit [*csh*(1)](/csh/1.md) style alternations (see Brace Expansion below); and, finally, **\***, **?** and **\[** are used in file name generation (see File Name Patterns below).

As words and tokens are parsed, the shell builds commands, of which there are two basic types: *simple-commands*, typically programs that are executed, and *compound-commands*, such as **for** and **if** statements, grouping constructs and function definitions.

A simple-command consists of some combination of parameter assignments (see Parameters below), input/output redirections (see Input/Output Redirections below), and command words; the only restriction is that parameter assignments come before any command words. The command words, if any, define the command that is to be executed and its arguments. The command may be a shell built-in command, a function or an *external* *command*, i.e., a separate executable file that is located using the **PATH** parameter (see Command Execution below). Note that all command constructs have an *exit status*: for external commands, this is related to the status returned by [*wait*(2)](/wait/2.md); the exit status of other command constructs (built-in commands, functions, compound-commands, pipelines, lists, etc.) are all well defined and are described where the construct is described. The exit status of a command consisting only of parameter assignments is that of the last command substitution performed during the parameter assignment or zero if there were no command substitutions.

Commands can be chained together using the **\|** token to form *pipelines*, in which the standard output of each command but the last is piped (see [*pipe*(2)](/pipe/2.md)) to the standard input of the following command. The exit status of a pipeline is that of its last command. A pipeline may be prefixed by the **!** reserved word which causes the exit status of the pipeline to be logically complemented: if the original status was 0 the complemented status will be 1, and if the original status was not 0, then the complemented status will be 0.

*Lists* of commands can be created by separating pipelines by any of the following tokens: **&&**, **\|\|**, **&**, **\|&** and **;**. The first two are for conditional execution: *cmd1* **&&** *cmd2* executes *cmd2* only if the exit status of *cmd1* is zero; **\|\|** is the opposite — *cmd2* is executed only if the exit status of *cmd1* is non-zero. **&&** and **\|\|** have equal precedence which is higher than that of **&**, **\|&** and **;**, which also have equal precedence. The **&** token causes the preceding command to be executed asynchronously, that is, the shell starts the command, but does not wait for it to complete (the shell does keep track of the status of asynchronous commands — see Job Control below). When an asynchronous command is started when job control is disabled (i.e., in most scripts), the command is started with signals INT and QUIT ignored and with input redirected from /dev/null (however, redirections specified in the asynchronous command have precedence). The **\|&** operator starts a *co-process* which is special kind of asynchronous process (see Co-Processes below). Note that a command must follow the **&&** and **\|\|** operators, while a command need not follow **&**, **\|&** and **;**. The exit status of a list is that of the last command executed, with the exception of asynchronous lists, for which the exit status is 0.

Compound commands are created using the following reserved words — these words are only recognized if they are unquoted and if they are used as the first word of a command (i.e., they can't be preceded by parameter assignments or redirections):

| | | | | |
| --- | --- | --- | --- | --- |
| **case** | **else** | **function** | **then** | **!** |
| **do** | **esac** | **if** | **time** | **\[\[** |
| **done** | **fi** | **in** | **until** | **{** |
| **elif** | **for** | **select** | **while** | **}** |

**Note:** Some shells (but not this one) execute control structure commands in a subshell when one or more of their file descriptors are redirected, so any environment changes inside them may fail. To be portable, the **exec** statement should be used instead to redirect file descriptors before the control structure.

In the following compound command descriptions, command lists (denoted as *list*) that are followed by reserved words must end with a semi-colon, a newline or a (syntactically correct) reserved word. For example,\
 **{ echo foo; echo bar; }** **{ echo foo; echo bar\<newline\>}** **{ { echo foo; echo bar; } }** are all valid, but\
 **{ echo foo; echo bar }** **is not.**

- **(** *list* **)**

  **Execute** *list* **in a subshell.  There is no implicit way to pass** **environment changes from a subshell back to its parent.**

- **{** *list* **}**

  **Compound construct;** *list* **is executed, but not in a subshell.** **Note that { and } are reserved words, not meta-characters.**

- **case** *word* **in** \[ \[**(**\] *pattern* \[**\|** *pattern*\] ... **)** *list* **;;** \] ... **esac**

  **The case statement attempts to match** *word* **against the specified** *pattern***s; the** *list* **associated with the first successfully matched** **pattern is executed.  Patterns used in case statements are the same as** **those used for file name patterns except that the restrictions regarding** **. and / are dropped.  Note that any unquoted space before and** **after a pattern is stripped; any space with a pattern must be quoted.  Both the** **word and the patterns are subject to parameter, command, and arithmetic** **substitution as well as tilde substitution.  The exit status of a case** **statement is that of the executed** *list***; if no** *list* **is executed,** **the exit status is zero.**

- **for** *name* \[ **in** *word* ... *term* \] **do** *list* **done**

  **where** *term* **is either a newline or a ;.** **For each** *word* **in the specified word list, the parameter** *name* **is** **set to the word and** *list* **is executed.  If in is not used to** **specify a word list, the positional parameters ("$1", "$2", etc.)** **are used instead.** **For historical reasons, open and close braces may be used instead** **of do and done (e.g., for i; { echo $i; }).** **The exit status of a for statement is the last exit status** **of** *list***; if** *list* **is never executed, the exit status is zero.**

- **if** *list* **then** *list* \[**elif** *list* **then** *list*\] ... \[**else** *list*\] **fi**

  **If the exit status of the first** *list* **is zero, the second** *list* **is executed; otherwise the** *list* **following the elif, if any, is** **executed with similar consequences.  If all the lists following the if** **and elifs fail (i.e., exit with non-zero status), the** *list* **following** **the else is executed.  The exit status of an if statement is that** **of non-conditional** *list* **that is executed; if no non-conditional** *list* **is executed, the exit status is zero.**

- **select** *name* \[ **in** *word* ... *term* \] **do** *list* **done**

  **where** *term* **is either a newline or a ;.** **The select statement provides an automatic method of presenting** **the user with a menu and selecting from it.** **An enumerated list of the specified** *words* **are printed on standard** **error, followed by a prompt (PS3, normally \`#? ').** **A number corresponding to one of the enumerated words is then read** **from standard input,** *name* **is set to the selected word (or is** **unset if the selection is not valid), REPLY** **is set to what was read, and** *list* **is executed.** **This process is repeated until an end-of-file is read, an interrupt is** **received or a break statement is executed inside the loop.** **If in** *word* **... is omitted, the positional parameters** **are used (i.e., "$1", "$2", etc.).** **For historical reasons, open and close braces may be used instead** **of do and done (e.g., select i; { echo $i; }).** **The exit status of a select statement is zero if a break statement** **is used to exit the loop, non-zero otherwise.**

- **until** *list* **do** *list* **done**

  **This works like while, except that the body is executed only while the** **exit status of the first** *list* **is non-zero.**

- **while** *list* **do** *list* **done**

  **A while is a prechecked loop.  Its body is executed as often** **as the exit status of the first** *list* **is zero.** **The exit status of a while statement is the last exit status** **of the** *list* **in the body of the loop; if the body is not executed,** **the exit status is zero.**

- **function** *name* **{** *list* **}**

  **Defines the function** *name***.** **See Functions below.** **Note that redirections specified after a function definition are** **performed whenever the function is executed, not when the function** **definition is executed.**

- *name* **()** *command*

  **Mostly the same as function.** **See Functions below.**

- **((** *expression* **))**

  **The arithmetic expression** *expression* **is evaluated;** **equivalent to let "***expression***".** **See Arithmetic Expressions and the let command below.**

- **\[\[** *expression* **\]\]**

  **Similar to the test and \[ ... \] commands (described later),** **with the following exceptions:**

  - •

    **Field splitting and file name generation are not performed on** **arguments.**

  - •

    **The -a (and) and -o (or) operators are replaced with** **&& and \|\|, respectively.**

  - •

    **Operators (e.g. -f, =, !, etc.) must be unquoted.**

  - •

    **The second operand of != and =** **expressions are patterns (e.g., the comparison in \[\[ foobar = f\*r \]\]** **succeeds)**

  - •

    **There are two additional binary operators: \< and \>** **which return true if their first string operand is less than,** **or greater than, their second string operand, respectively.**

  - •

    **The single argument form** **of test, which tests if the argument has non-zero length, is not valid** **- explicit operators must be always be used, e.g., instead of**\
     **\[** *str* **\]** **use**\
     **\[\[ -n***str* **\]\]**

  - •

    **Parameter, command and arithmetic substitutions are performed as** **expressions are evaluated and lazy expression evaluation is used for** **the && and \|\| operators.** **This means that in the statement \[\[ -r foo && $(\< foo) = b\*r \]\], the** **$(\< foo) is evaluated if and only if the file foo exists.**

### Quoting

**Quoting is used to prevent the shell from treating characters or words** **specially.** **There are three methods of quoting: First, \\ quotes** **the following character, unless it is at the end of a line, in which** **case both the \\ and the newline are stripped.** **Second, a single quote (') quotes everything up to the next single** **quote (this may span lines).** **Third, a double quote (") quotes all characters,** **except $, \` and \\, up to the next unquoted double quote.** **$ and \` inside double quotes have their usual meaning (i.e.,** **parameter, command or arithmetic substitution) except no field splitting** **is carried out on the results of double-quoted substitutions.** **If a \\ inside a double-quoted string is followed by \\, $,** **\` or ", it is replaced by the second character; if it is** **followed by a newline, both the \\ and the newline are stripped;** **otherwise, both the \\ and the character following are unchanged.**

**Note: see POSIX Mode below for a special rule regarding sequences** **of the form "...\`...\\"...\`..".**

### Aliases

**There are two types of aliases: normal command aliases and tracked** **aliases.  Command aliases are normally used as a short hand for a long** **or often used command.  The shell expands command aliases (i.e.,** **substitutes the alias name for its value) when it reads the first word** **of a command.  An expanded alias is re-processed to check for more** **aliases.  If a command alias ends in a space or tab, the following word** **is also checked for alias expansion.  The alias expansion process stops** **when a word that is not an alias is found, when a quoted word is found** **or when an alias word that is currently being expanded is found.**

**The following command aliases are defined automatically by the shell:**

```
autoload='typeset -fu'
functions='typeset -f'
hash='alias -t --'
history='fc -l'
integer='typeset -i'
local='typeset'
login='exec login'
newgrp='exec newgrp'
nohup='nohup '
r='fc -e -'
stop='kill -STOP'
suspend='kill -STOP $$'
type='whence -v'
```

**Tracked aliases allow the shell to remember where it found a particular** **command.  The first time the shell does a path search for a command that** **is marked as a tracked alias, it saves the full path of the command.** **The next time the command is executed, the shell checks the saved path** **to see that it is still valid, and if so, avoids repeating the path** **search.  Tracked aliases can be listed and created using alias** **-t.  Note that changing the PATH parameter clears the saved** **paths for all tracked aliases.  If the trackall option is set (i.e.,** **set -o trackall or set -h), the shell tracks all** **commands.  This option is set automatically for non-interactive shells.** **For interactive shells, only the following commands are automatically** **tracked: cat, cc, chmod, cp, date, ed,** **emacs, grep, ls, mail, make, mv,** **pr, rm, sed, sh, vi and who.**

### Substitution

**The first step the shell takes in executing a simple-command is to** **perform substitutions on the words of the command.** **There are three kinds of substitution: parameter, command and arithmetic.** **Parameter substitutions, which are described in detail in the next section,** **take the form $name or ${...}; command substitutions take** **the form $(***command***) or \`***command***\`;** **and arithmetic substitutions take the form $((***expression***)).**

**If a substitution appears outside of double quotes, the results of the** **substitution are generally subject to word or field splitting according to** **the current value of the IFS parameter.** **The IFS parameter specifies a list of characters which**  **are used to break a string up into several words;** **any characters from the set space, tab and newline that appear in the** **IFS characters are called** *IFS white space***.** **Sequences of one or more IFS white space characters, in combination with** **zero or one non-IFS white space characters delimit a field.** **As a special case, leading and trailing IFS white space is stripped (i.e.,** **no leading or trailing empty field is created by it); leading or trailing** **non-IFS white space does create an empty field.** **Example: if IFS is set to \`\<space\>:', the sequence of characters** **\`\<space\>A\<space\>:\<space\>\<space\>B::D' contains four fields: \`A', \`B', \`' and \`D'.** **Note that if the IFS parameter is set to the null string, no** **field splitting is done; if the parameter is unset, the default value** **of space, tab and newline is used.**

**The results of substitution are, unless otherwise specified, also subject** **to brace expansion and file name expansion (see the relevant sections** **below).**

**A command substitution is replaced by the output generated by the specified** **command, which is run in a subshell.** **For $(***command***) substitutions, normal quoting rules** **are used when** *command* **is parsed, however, for the** **\`***command***\` form, a \\ followed by any of** **$, \` or \\ is stripped (a \\ followed by any other** **character is unchanged).** **As a special case in command substitutions, a command of the form** **\<** *file* **is interpreted to mean substitute the contents** **of** *file* **($(\< foo) has the same effect as $(cat foo), but it** **is carried out more efficiently because no process is started).**\
 **NOTE: $(***command***) expressions are currently parsed by** **finding the matching parenthesis, regardless of quoting.  This will hopefully** **be fixed soon.**

**Arithmetic substitutions are replaced by the value of the specified** **expression.** **For example, the command echo $((2+3\*4)) prints 14.** **See Arithmetic Expressions for a description of an** *expression***.**

### Parameters

**Parameters are shell variables; they can be assigned values and** **their values can be accessed using a parameter substitution.** **A parameter name is either one of the special single punctuation or digit** **character parameters described below, or a letter followed by zero or more** **letters or digits (\`\_' counts as a letter).** **Parameter substitutions take the form $***name* **or** **${***name***}, where** *name* **is a parameter name.** **If substitution is performed on a parameter that is not set, a null** **string is substituted unless the nounset option (set -o nounset** **or set -u) is set, in which case an error occurs.**

**Parameters can be assigned values in a number of ways.** **First, the shell implicitly sets some parameters like #, PWD,** **etc.; this is the only way the special single character parameters are** **set.** **Second, parameters are imported from the shell's environment at startup.** **Third, parameters can be assigned values on the command line, for example,** **\`FOO=bar' sets the parameter FOO to bar; multiple parameter** **assignments can be given on a single command line and they can** **be followed by a simple-command, in which case the assignments are** **in effect only for the duration of the command (such assignments are** **also exported, see below for implications of this).** **Note that both the parameter name and the = must be unquoted for** **the shell to recognize a parameter assignment.** **The fourth way of setting a parameter is with the export, readonly** **and typeset commands; see their descriptions in the Command Execution** **section.** **Fifth, for and select loops set parameters as well as** **the getopts, read and set -A commands.** **Lastly, parameters can be assigned values using assignment operators** **inside arithmetic expressions (see Arithmetic Expressions below) or** **using the ${***name***=***value***} form** **of parameter substitution (see below).**

**Parameters with the export attribute (set using the export or** **typeset -x commands, or by parameter assignments followed by simple** **commands) are put in the environment (see** *environ***(5)) of commands** **run by the shell as** *name***=***value* **pairs.** **The order in which parameters appear in the environment of a command** **is unspecified.** **When the shell starts up, it extracts parameters and their values from its** **environment and automatically sets the export attribute for those parameters.**

**Modifiers can be applied to the ${***name***} form of parameter** **substitution:**

- **${***name***:-***word***}**

  **if** *name* **is set and not null, it is substituted, otherwise** *word* **is** **substituted.**

- **${***name***:+***word***}**

  **if** *name* **is set and not null,** *word* **is substituted, otherwise nothing is substituted.**

- **${***name***:=***word***}**

  **if** *name* **is set and not null, it is substituted, otherwise it is** **assigned** *word* **and the resulting value of** *name* **is substituted.**

- **${***name***:?***word***}**

  **if** *name* **is set and not null, it is substituted, otherwise** *word* **is printed on standard error (preceded by** *name***:) and an error occurs** **(normally causing termination of a shell script, function or .-script).** **If word is omitted the string \`parameter null or not set' is used instead.**

**In the above modifiers, the : can be omitted, in which case the** **conditions only depend on** *name* **being set (as opposed to set and** **not null).** **If** *word* **is needed, parameter, command, arithmetic and tilde substitution** **are performed on it; if** *word* **is not needed, it is not evaluated.**

**The following forms of parameter substitution can also be used:**

- **${#***name***}**

  **The number of positional parameters if** *name* **is \*, @ or** **is not specified,** **the number of elements in the named array if** *name* **is an array,** **or finally, the length of the string value of parameter** *name***.**

- **${***name***#***pattern***}**, **${***name***##***pattern***}**

  **If** *pattern* **matches the beginning of the value of parameter** *name***,** **the matched text is deleted from the result of substitution.  A single** **# results in the shortest match, two #'s results in the** **longest match.**

- **${***name***%***pattern***}**, **${***name***%%***pattern***}**

  **Like ${..#..} substitution, but it deletes from the end of the** **value.**

**The following special parameters are implicitly set by the shell and cannot be** **set directly using assignments:**

- **!**

  **Process id of the last background process started.  If no background** **processes have been started, the parameter is not set.**

- **#**

  **The number of positional parameters (i.e., $1, $2, etc.).**

- **$**

  **The process ID of the shell, or the PID of the original shell if** **it is a subshell.**

- **-**

  **The concatenation of the current single letter options** **(see set command below for list of options).**

- **?**

  **The exit status of the last non-asynchronous command executed.** **If the last command was killed by a signal, $? is set to 128 plus** **the signal number.**

- **0**

  **The name the shell was invoked with (i.e., argv\[0\]), or the** **command-name if it was invoked with the -c option and the** **command-name was supplied, or the** *file* **argument, if it was** **supplied.** **If the posix option is not set, $0 is the name of the current** **function or script.**

- **1** ... **9**

  **The first nine positional parameters that were supplied to the shell,** **function or .-script.** **Further positional parameters may be accessed using** **${***number***}.**

- **\***

  **All positional parameters (except parameter 0),**  **i.e., $1 $2 $3....** **If used outside of double quotes, parameters are separate words** **(which are subjected to word splitting); if used within double quotes,** **parameters are separated by the first character if the IFS parameter** **(or the empty string if IFS is null).**

- **@**

  **Same as $\*, unless it is used inside double quotes, in which case** **a separate word is generated for each positional parameter - if there** **are no positional parameters, no word is generated ("$@" can be used** **to access arguments, verbatim, without loosing null arguments or** **splitting arguments with spaces).**

**The following parameters are set and/or used by the shell:**

- **\_** *(underscore)*

  **In interactive use, this parameter is set to the last word of the** **previous command.  When a command is executed, this parameter is set to** **the full path of the command and is placed in the command's environment.** **When MAILPATH messages are evaluated, this parameter contains** **the name of the file that changed (see MAILPATH parameter below).**

- **CDPATH**

  **Search path for the cd built-in command.  Works the same way as** **PATH for those directories not beginning with / in cd** **commands.** **Note that if CDPATH is set and does not contain . nor an empty path,** **the current directory is not searched.**

- **COLUMNS**

  **Set to the number of columns on the terminal or window.** **Currently set to the cols value as reported by** *stty***(1) if that** **value is non-zero.** **This parameter is used by the interactive line editing modes, and by** **select, set -o and kill -l commands** **to format information in columns.**

- **EDITOR**

  **If the VISUAL parameter is not set, this parameter controls the** **command line editing mode for interactive shells.** **See VISUAL parameter below for how this works.**

- **ENV**

  **If this parameter is found to be set after any profile files are** **executed, the expanded value is used as a shell start-up file.  It** **typically contains function and alias definitions.**

- **ERRNO**

  **Integer value of the shell's errno variable — indicates the reason** **the last system call failed.**

  **Not implemented yet.**

- **EXECSHELL**

  **If set, this parameter is assumed to contain the shell that is to be** **used to execute commands that** *execve***(2) fails to execute and** **which do not start with a \`#!** *shell***' sequence.**

- **FCEDIT**

  **The editor used by the fc command (see below).**

- **FPATH**

  **Like PATH, but used when an undefined function is executed to locate** **the file defining the function.** **It is also searched when a command can't be found using PATH.** **See Functions below for more information.**

- **HISTFILE**

  **The name of the file used to store history.** **When assigned to, history is loaded from the specified file.** **Also, several invocations of the** **shell running on the same machine will share history if their** **HISTFILE parameters all point at the same file.**\
   **NOTE: if HISTFILE isn't set, no history file is used.  This is** **different from the original Korn shell, which uses $HOME/.sh\_history;** **in future, pdksh may also use a default history file.**

- **HISTSIZE**

  **The number of commands normally stored for history, default 128.**

- **HOME**

  **The default directory for the cd command and the value** **substituted for an unqualified ~ (see Tilde Expansion below).**

- **IFS**

  **Internal field separator, used during substitution and by the read** **command, to split values into distinct arguments; normally set to** **space, tab and newline.  See Substitution above for details.**\
   **Note: this parameter is not imported from the environment** **when the shell is started.**

- **KSH\_VERSION**

  **The version of shell and the date the version was created (readonly).** **See also the version commands in Emacs Interactive Input Line Editing** **and Vi Interactive Input Line Editing, below.**

- **LINENO**

  **The line number of the function or shell script that is currently being** **executed.**

  **Not implemented yet.**

- **LINES**

  **Set to the number of lines on the terminal or window.**

  **Not implemented yet.**

- **MAIL**

  **If set, the user will be informed of the arrival of mail in the named** **file.  This parameter is ignored if the MAILPATH parameter is set.**

- **MAILCHECK**

  **How often, in seconds, the shell will check for mail in the file(s)** **specified by MAIL or MAILPATH.  If 0, the shell checks** **before each prompt.  The default is 600 (10 minutes).**

- **MAILPATH**

  **A list of files to be checked for mail.  The list is colon separated,** **and each file may be followed by a ? and a message to be printed** **if new mail has arrived.  Command and parameter substitution is** **performed on the message, and, during substitution, the parameter $\_** **contains the name of the file.** **The default message is you have mail in $\_.**

- **OLDPWD**

  **The previous working directory.** **Unset if cd has not successfully changed directories since the** **shell started, or if the shell doesn't know where it is.**

- **OPTARG**

  **When using getopts, it contains the argument for a parsed option,** **if it requires one.**

- **OPTIND**

  **The index of the last argument processed when using getopts.** **Assigning 1 to this parameter causes getopts to** **process arguments from the beginning the next time it is invoked.**

- **PATH**

  **A colon separated list of directories that are searched when looking** **for commands and .'d files.** **An empty string resulting from a leading or trailing colon, or two adjacent** **colons is treated as a \`.', the current directory.**

- **POSIXLY\_CORRECT**

  **If set, this parameter causes the posix option to be enabled.** **See POSIX Mode below.**

- **PPID**

  **The process ID of the shell's parent (readonly).**

- **PS1**

  **PS1 is the primary prompt for interactive shells.** **Parameter, command and arithmetic substitutions are performed, and** **! is replaced with the current command number (see fc** **command below).  A literal ! can be put in the prompt by placing !! in PS1.** **Default is \`$ '.**

- **PS2**

  **Secondary prompt string, by default \`\> ', used when more input is** **needed to complete a command.**

- **PS3**

  **Prompt used by select statement when reading a menu selection.** **Default is \`#? '.**

- **PS4**

  **Used to prefix commands that are printed during execution tracing** **(see set -x command below).** **Parameter, command and arithmetic substitutions are performed** **before it is printed.** **Default is \`+ '.**

- **PWD**

  **The current working directory.  Maybe unset or null if shell doesn't** **know where it is.**

- **RANDOM**

  **A simple random number generator.  Every time RANDOM is** **referenced, it is assigned the next number in a random number series.** **The point in the series can be set by assigning a number to** **RANDOM (see** *rand***(3)).**

- **REPLY**

  **Default parameter for the read command if no names are given.** **Also used in select loops to store the value that is read from** **standard input.**

- **SECONDS**

  **The number of seconds since the shell started or, if the parameter has been** **assigned an integer value, the number of seconds since the assignment plus** **the value that was assigned.**

- **TMOUT**

  **If set to a positive integer in an interactive shell, it specifies** **the maximum number of seconds the shell will wait for input after** **printing the primary prompt (PS1).  If the time is exceeded, the** **shell exits.**

- **TMPDIR**

  **The directory shell temporary files are created in.  If this parameter** **is not set, or does not contain the absolute path of a writable** **directory, temporary files are created in /tmp.**

- **VISUAL**

  **If set, this parameter controls the command line editing mode for** **interactive shells.  If the last component of the path specified in this** **parameter contains the string vi, emacs or gmacs, the** **vi, emacs or gmacs (Gosling emacs) editing mode is enabled, respectively.**

### Tilde Expansion

**Tilde expansion, which is done in parallel with parameter substitution,** **is done on words starting with an unquoted ~.  The characters** **following the tilde, up to the first /, if any, are assumed to be** **a login name.  If the login name is empty, + or -, the** **value of the HOME, PWD, or OLDPWD parameter is** **substituted, respectively.  Otherwise, the password file is searched for** **the login name, and the tilde expression is substituted with the** **user's home directory.  If the login name is not found in the password** **file or if any quoting or parameter substitution occurs in the login name,** **no substitution is performed.**

**In parameter assignments (those preceding a simple-command or those** **occurring in the arguments of alias, export, readonly,** **and typeset), tilde expansion is done after any unquoted colon** **(:), and login names are also delimited by colons.**

**The home directory of previously expanded login names are cached and** **re-used.  The alias -d command may be used to list, change and** **add to this cache (e.g., \`alias -d fac=/usr/local/facilities; cd** **~fac/bin').**

### Brace Expansion (alternation)

**Brace expressions, which take the form**\
 *prefix***{***str***1,...,***str***N}***suffix* **are expanded to N words, each of which is the concatenation of** *prefix***,** *str***i and** *suffix* **(e.g., \`a{c,b{X,Y},d}e' expands to four word: ace, abXe, abYe, and ade).** **As noted in the example, brace expressions can be nested and the resulting** **words are not sorted.** **Brace expressions must contain an unquoted comma (,) for expansion** **to occur (i.e., {} and {foo} are not expanded).** **Brace expansion is carried out after parameter substitution and before** **file name generation.**

### File Name Patterns

**A file name pattern is a word containing one or more unquoted ? or** **\* characters or \[..\] sequences.  Once brace expansion has** **been performed, the shell replaces file name patterns with the sorted names** **of all the files that match the pattern (if no files match, the word is** **left unchanged).  The pattern elements have the following meaning:**

- **?**

  **matches any single character.**

- **\***

  **matches any sequence of characters.**

- **\[**..**\]**

  **matches any of the characters inside the brackets.  Ranges of characters** **can be specified by separating two characters by a -, e.g., \[a0-9\]** **matches the letter a or any digit.  In order to represent itself, a** **- must either be quoted or the first or last character in the character** **list.  Similarly, a \] must be quoted or the first character in the list** **if it is represent itself instead of the end of the list.  Also, a !** **appearing at the start of the list has special meaning (see below), so to** **represent itself it must be quoted or appear later in the list.**

- **\[!**..**\]**

  **like \[..\], except it matches any character not inside the brackets.**

**Note that pdksh currently never matches . and .., but the original** **ksh, Bourne sh and bash do, so this may have to change (too bad).**

**Note that none of the above pattern elements match either a period (.)** **at the start of a file name or a slash (/), even if they are explicitly** **used in a \[..\] sequence; also, the names . and ..** **are never matched, even by the pattern .\*.**

**If the markdirs option is set, any directories that result from** **file name generation are marked with a trailing /.**

**The ?(***pattern-list***), \*(***p-l***),** **+(***p-l***), @(***p-l***) and !(***p-l***)** **elements found in the original Korn shell are not yet implemented; the same** **is true for the POSIX character classes (i.e.,** **\[:***class-name***:\] inside a \[..\] expression).**

### Input/Output Redirection

**When a command is executed, its standard input, standard output and** **standard error (file descriptors 0, 1 and 2, respectively) are normally** **inherited from the shell.** **Three exceptions to this are commands in pipelines, for which standard input** **and/or standard output are those set up by the pipeline, asynchronous commands** **created when job control is disabled, for which standard input is initially** **set to be from /dev/null, and commands for which any of the following** **redirections have been specified:**

- **\>** *file*

  **standard output is redirected to** *file***.  If** *file* **does not exist,** **it is created; if it does exist and the noclobber option is set, an** **error occurs, otherwise the file is truncated.** **Note that this means the command** *cmd \< foo \> foo* **will open** *foo* **for reading and then truncate it when it opens it for writing,** **before** *cmd* **gets a chance to actually read** *foo***.**

- **\>\|** *file*

  **same as \>, except the file is truncated, even if the noclobber** **option is set.**

- **\>\>** *file*

  **same as \>, except the file an existing file is appended to instead** **of being truncated.  Also, the file is opened in append mode, so writes** **always go to the end of the file (see** *open***(2)).**

- **\<** *file*

  **standard input is redirected from** *file***, which is opened for reading.**

- **\<\>** *file*

  **same as \<, except the file is opened for reading and writing.**

- **\<\<** *marker*

  **after reading the command line containing this kind of redirection (called a** **here document), the shell copies lines from the command source into a temporary** **file until a line matching** *marker* **is read.** **When the command is executed, standard input is redirected from the temporary** **file.** **If** *marker* **contains no quoted characters, the contents of the** **temporary file are processed as if enclosed in double quotes each time** **the command is executed, so parameter, command and arithmetic substitutions** **are performed, along with backslash (\\) escapes for** **$, \`, \\ and \\newline.** **If multiple here documents are used on the same command line, they are** **saved in order.**

- **\<\<-** *marker*

  **same as \<\<, except leading tabs are stripped from lines in the** **here document.**

- **\<&** *fd*

  **standard input is duplicated from file descriptor** *fd***.** *fd* **can be a single digit, indicating the number of an existing** **file descriptor, the letter p, indicating the file descriptor** **associated with the output of the current co-process, or** **the character -, indicating standard input is to be closed.**

- **\>&** *fd*

  **same as \<&, except the operation is done on standard output.**

**In any of the above redirections, the file descriptor that is redirected** **(i.e., standard input or standard output) can be explicitly given by preceding** **the redirection with a single digit.** **Parameter, command and arithmetic substitutions, tilde substitutions and** **file name generation are all performed on the** *file***,** *marker* **and** *fd* **arguments of redirections.** **Note however, that the results of any file name generation are only used** **if a single file is matched; if multiple files match, the word with the** **unexpanded file name generation characters is used.** **Note that in restricted shells, redirections which can create files cannot** **be used.**

**For simple-commands, redirections may appear anywhere in the command, for** **compound-commands (if statements, etc.), any redirections must** **appear at the end.** **Redirections are processed after pipelines are created and in the order they** **are given, so**\
 **cat /foo/bar 2\>&1 \> /dev/null \| cat -n** **will print an error with a line number prepended to it.**

### Arithmetic Expressions

**Integer arithmetic expressions can be used with the let command,** **inside $((..)) expressions,** **inside array references (e.g.,** *name***\[***expr***\]),** **as numeric arguments to the test command,** **and as the value of an assignment to an integer parameter.**

**Expression may contain alpha-numeric parameter identifiers, array** **references, and integer constants and may be combined with the** **following C operators (listed and grouped in increasing order of precedence).**

- **Unary operators:**

  **+ - ! ~**

- **Binary operators:**

  **= \*= /= %= += -= \<\<= \>\>= &= ^= \|=**\
   **\|\|**\
   **&&**\
   **\|**\
   **^**\
   **&**\
   **== !=**\
   **\< \<= \>= \>**\
   **\<\< \>\>**\
   **+ -**\
   **\* / %**

- **Ternary operator:**

  **?: (precedence is immediately higher than assignment)**

- **Grouping operators:**

  **( )**

**Integer constants may be specified with arbitrary bases using the notation** *base***#***number***, where** *base* **is a decimal integer specifying** **the base, and** *number* **is a number in the specified base.**

**The operators are evaluated as follows:**

- unary **+**

  **result is the argument (included for completeness).**

- unary **-**

  **negation.**

- **!**

  **logical not; the result is 1 if argument is zero, 0 if not.**

- **~**

  **arithmetic (bit-wise) not.**

- **=**

  **assignment; variable on the left is set to the value on the right.**

- **\*= /= %= += -= \<\<= \>\>= &= ^= \|=**

  **assignment operators;** *\<var\> \<op\>***=** *\<expr\>* **is the same as** *\<var\>* **=** *\<var\> \<op\>* **(** *\<expr\>* **).**

- **\|\|**

  **logical or; the result is 1 if either argument is non-zero, 0 if not.** **The right argument is evaluated only if the left argument is zero.**

- **&&**

  **logical and; the result is 1 if both arguments are non-zero, 0 if not.** **The right argument is evaluated only if the left argument is non-zero.**

- **\|**

  **arithmetic (bit-wise) or.**

- **^**

  **arithmetic (bit-wise) exclusive-or.**

- **&**

  **arithmetic (bit-wise) and.**

- **==**

  **equal; the result is 1 if both arguments are equal, 0 if not.**

- **!=**

  **not equal; the result is 0 if both arguments are equal, 1 if not.**

- **\<**

  **less than; the result is 1 if the left argument is less than the right,** **0 if not.**

- **\<= \>= \>**

  **less than or equal, greater than or equal, greater than.  See \<.**

- **\<\< \>\>**

  **shift left (right); the result is the left argument with its bits shifted** **left (right) by the amount given in the right argument.**

- **+ - \* /**

  **addition, subtraction, multiplication, and division.**

- **%**

  **remainder; the result is the remainder of the division of the left argument** **by the right.  The sign of the result is unspecified if either argument** **is negative.**

- *\<arg1\>* **?** *\<arg2\>* **:** *\<arg3\>*

  **if** *\<arg1\>* **is non-zero, the result is** *\<arg2\>***,** **otherwise** *\<arg3\>***.**

### Co-Processes

**A Co-process, which is a pipeline created with the \|& operator,** **is an asynchronous process that the shell can both write to** **(using print -p) and read from (using read -p).** **Only one co-process may be active at any given time, unless the input** **of an existing co-process has been duplicated using a \>&p redirection.** **In this case, the shell closes its copy of the co-process input (note** **that a \<&p redirection does not cause the shell to close its copy** **of the co-process output).** **Once read -p has read the end-of-file, the co-process input is** **closed, and further attempts to read will produce diagnostics.** **Similarly, once print -p fails due to an EPIPE, the co-process** **output is closed.** **Note also, that print -p will ignore SIGPIPE signals during writes** **if the signal is not being trapped or ignored; the same is not true if** **the co-process input has been duplicated to another file descriptor and** **print -u***n* **is used.**

**If another co-process is started before doing a read or \<&p redirection** **from existing co-processes, the output of the co-processes will be shared** **(e.g., echo hi \|& echo there\|& cat \<&p will print both "hi" and "there").** **This is slightly different from the original Korn shell in which output is** **shared as long as the existing co-process job has not exited.** **As a side affect, end-of-file can not be read reliably in the original Korn** **shell (e.g., if the co-process closes its output but does not exit, the** **end of file will not be read).**

### Functions

**Functions are defined using either Korn shell function** *name* **syntax or the Bourne/POSIX shell** *name***() syntax.** **At the moment, there is no difference between the two, but see below.** **Functions are like .-scripts in that they are executed in** **the current environment, however, unlike .-scripts, shell arguments** **(i.e., positional parameters, $1, etc.) are never visible inside them.** **When the shell is determining the location of as command, functions are** **searched after special built-in commands, and before regular and non-regular** **built-ins, and before the PATH is searched.**

**An existing function may be deleted using unset -f** *function-name***.** **A list of functions can be obtained using typeset +f and the** **function definitions can be listed using typeset -f.** **autoload (which is an alias for typeset -fu) may be used to** **create undefined functions; when an undefined function is executed, the** **shell searches the path specified in the FPATH parameter for a file** **with the same name as the function, which, if found is read and executed.** **If after executing the file, the named function is found to be defined, the** **function is executed, otherwise, the normal command search is continued** **(i.e., the shell searches the regular built-in command table and PATH).** **Note that if a command is not found using PATH, an attempt is** **made to autoload a function using FPATH (this is an undocumented** **feature of the original Korn shell).**

**Functions can have two attributes, trace and export, which can be set** **with typeset -ft and typeset -fx, respectively.** **When a traced function is executed, the shell's xtrace option is turned** **on for the functions duration, otherwise the xtrace option is turned off.** **The export attribute of functions is currently not used.  In the original** **Korn shell, exported functions are visible to shell scripts that are executed.**

**Since functions are executed in the current shell environment, parameter** **assignments made inside functions are visible after the function completes.** **If this is not the desired effect, the typeset command can be used** **inside a function to create a local parameter.** **Note that special parameters (e.g., $$, $!) can't be scoped in** **this way.**

**The exit status of a function is that of the last command executed in** **the function.** **A function can be made to finish immediately using the return command;** **this may also be used to explicitly specify the exit status.**

**In the future, functions defined with the function reserved word will** **be treated differently in the following ways from functions defined with** **the () notation:**

- •

  **A separate trap/signal environment will be used during the execution of** **functions.** **This will mean that traps set inside a function will not affect the shell's** **traps and signals that are not ignored in the shell (but may be trapped) will** **have their default effect in a function.**

- •

  **The EXIT trap, if set in a function, will be executed after the function** **returns.**

- •

  **the $0 parameter will be set to the name of the function (this is** **currently the case for both styles of function).**

### POSIX Mode

**The shell is intended to be POSIX compliant, however, in some cases, POSIX** **behaviour is contrary either to the original Korn shell behaviour or to** **user convenience.** **How the shell behaves in these cases is determined by the state of** **the posix option (set -o posix) — if it is on, the POSIX behaviour** **is followed, otherwise it is not.** **The posix option is set automatically when the shell starts up** **if the environment contains the POSIXLY\_CORRECT parameter.** **(The shell can also be compiled so that it is in POSIX mode by default,** **however this is usually not desirable).**

**The following is a list of things that are affected by the state of** **the posix option:**

- •

  **\\" inside double quoted \`..\` command substitutions:** **in posix mode, the \\" is interpreted when the command is interpreted;** **in non-posix mode, the backslash is stripped before the command substitution** **is interpreted.  For example, echo "\`echo \\"hi\\"\`" produces \`"hi"' in** **posix mode, \`hi' in non-posix mode.  To avoid problems, use the $(...)** **form of command substitution.**

- •

  **kill -l output: in posix mode, signal names are listed one a single line;** **in non-posix mode, signal numbers, names and descriptions are printed in** **columns.** **In future, a new option (-v perhaps) will be added to distinguish** **the two behaviours.**

- •

  **fg exit status: in posix mode, the exit status is 0 if no errors occur;** **in non-posix mode, the exit status is that of the last foregrounded job.**

- •

  **$0: in posix mode, it is always the name of the shell; in non-posix** **mode, it is the name of the current function or script while a function or** **script is being executed.**

- •

  **getopts: in posix mode, options must start with a -; in non-posix** **mode, options can start with either - or +.**

- •

  **brace expansion (also known as alternation): in posix mode, brace expansion** **is disabled; in non-posix mode, brace expansion enabled.** **Note that set -o posix (or setting the POSIXLY\_CORRECT parameter)** **automatically turns the braceexpand option off, however it can be** **explicitly turned on later.**

- •

  **set -: in posix mode, this does not clear the verbose or** **xtrace options; in non-posix mode, it does.**

- •

  **set exit status: in posix mode, the exit status of set is 0** **if there are no errors; in non-posix mode, the exit status is that of** **any command substitutions performed in generating the set command.** **For example, \`set -- \`false\`; echo $?' prints 0 in posix mode,** **1 in non-posix mode.  This construct is used in most shell scripts that** **use the old** *getopt***(1) command.**

- •

  **argument expansion of alias, export, readonly, and** **typeset commands: in posix mode, normal argument expansion done;** **in non-posix mode, field splitting, file globing, brace expansion and** **(normal) tilde expansion are turned off, and assignment tilde expansion** **is turned on.**

- •

  **signal specification: in posix mode, signals can be specified as digits only** **if signal numbers match POSIX values (i.e., HUP=1, INT=2, QUIT=3, ABRT=6,** **KILL=9, ALRM=14, and TERM=15); in non-posix mode, signals can be always digits.**

- •

  **alias expansion: in posix mode, alias expansion is only carried out when** **reading command words; in non-posix mode, alias expansion is carried out** **on any word following an alias that ended in a space.** **For example, the following for loop**

  ```
  alias a='for ' i='j'
  a i in 1 2; do echo i=$i j=$j; done
  ```

  **uses parameter i in posix mode, j in non-posix mode.**

### Command Execution

**After evaluation of command line arguments, redirections and parameter** **assignments, the type of command is determined: a special built-in,** **a function, a regular built-in or the name of a file to execute found** **using the PATH parameter.** **The checks are made in the above order.** **Special built-in commands differ from other commands in that**  **the PATH parameter is not used to find them, an error** **during their execution can cause a non-interactive shell to exit and** **parameter assignments that are specified before the command are** **kept after the command completes.** **Just to confuse things, if the posix option is turned off (see set** **command below) some special commands are very special in that** **no field splitting, file globing, brace expansion nor tilde expansion** **is preformed on arguments that look like assignments.** **Regular built-in commands are different only in that the PATH** **parameter is not used to find them.**

**The original ksh and POSIX differ somewhat in which commands are considered** **special or regular:**

- POSIX special commands

  | | | | | |
  | --- | --- | --- | --- | --- |
  | **.** | **continue** | **exit** | **return** | **trap** |
  | **:** | **eval** | **export** | **set** | **unset** |
  | **break** | **exec** | **readonly** | **shift** |

- Addition ksh special commands

  | | | | | |
  | --- | --- | --- | --- | --- |
  | **builtin** | **times** | **typeset** |  |  |

- Very special commands (non-posix mode)

  | | | | | |
  | --- | --- | --- | --- | --- |
  | **alias** | **readonly** | **set** | **typeset** |  |

- POSIX regular commands

  | | | | | |
  | --- | --- | --- | --- | --- |
  | **alias** | **command** | **fg** | **kill** | **umask** |
  | **bg** | **false** | **getopts** | **read** | **unalias** |
  | **cd** | **fc** | **jobs** | **true** | **wait** |

- Addition ksh regular commands

  | | | | | |
  | --- | --- | --- | --- | --- |
  | **\[** | **let** | **pwd** | **ulimit** |  |
  | **echo** | **print** | **test** | **whence** |  |

**In the future, the additional ksh special and regular commands may** **be treated differently from the POSIX special and regular commands.**

**Once the type of the command has been determined, any command line parameter** **assignments are performed and exported for the duration of the command.**

**The following describes the special and regular built-in commands:**

- **.** *file* \[*arg1* ...\]

  **Execute the commands in** *file* **in the current environment.** **The file is searched for in the directories of PATH.** **If arguments are given, the positional parameters may be used to** **access them while** *file* **is being executed.** **If no arguments are given, the positional parameters are those of the** **environment the command is used in.**

- **:** \[ ... \]

  **The null command.** **Exit status is set to zero.**

- **alias** \[ **-d** \| **-t** \[**-r**\] \] \[**-x**\] \[*name1*\[**=***value1*\] ...\]

  **Without arguments, alias lists all aliases and their values.  For** **any name without a value, its value is listed.  Any name with a value** **defines an alias (see Aliases above).**

  **The -x option sets the export attribute of an alias, or, if no** **names are given, lists the aliases with the export attribute** **(exporting an alias currently has no affect).**

  **The -t option indicates that tracked aliases are to be listed/set** **(values specified on the command line are ignored for tracked aliases).** **The -r option indicates that all tracked aliases are to be reset.**

  **The -d causes directory aliases, which are used in tilde expansion,** **to be listed or set (see Tilde Expansion above).**

- **bg** \[*job* ...\]

  **Resume the specified stopped job(s) in the background.** **If no jobs are specified, %+ is assumed.** **This command is only available on systems which support job control.** **See Job Control below for more information.**

- **bind** \[**-m**\] \[*key*\[**=***editing-command*\] ...\]

  **Set or view the current emacs command editing key bindings/macros.** **See Emacs Interactive Input Line Editing below for a complete description.**

- **break** \[*level*\]

  **break exits the** *level***th inner most for, select, until, or while** **loop.** *level* **defaults to 1.**

- **builtin** *command* \[*arg1* ...\]

  **Execute the built-in command** *command***.**

- **cd** \[**-LP**\] \[*dir*\]

  **Set the working directory to** *dir***.  If the parameter CDPATH** **is set, it lists the search path for the directory containing** *dir***.  A null path mans the current directory.  If** *dir* **is** **missing, the home directory $HOME is used.  If** *dir* **is** **-, the previous working directory is used (see OLDPWD parameter).** **If -L option (logical path) is used or if the physical option** **(see set command below) isn't set, references to .. in** *dir* **are relative to the path used get to the directory.** **If -P option (physical path) is used or if the physical option** **is set, .. is relative to the filesystem directory tree.** **The PWD and OLDPWD parameters are updated to reflect the** **current and old wording directory, respectively.**

- **cd** \[**-LP**\] *old new*

  **The string** *new* **is substituted for** *old* **in the current** **directory, and the shell attempts to change to the new directory.**

- **command** \[**-pvV**\] *cmd* \[*arg1* ...\]

  **If neither the -v nor -V options are given,** *cmd* **is executed exactly as if the command had not been specified,** **with two exceptions: first,** *cmd* **cannot be a shell function, and** **second, special built-in commands lose their specialness (i.e., redirection** **and utility errors do not cause the shell to exit, and command assignments** **are not permanent).** **If the -p option is given, a default search path is used instead of** **the current value of PATH (the actual value of the default path is** **system dependent: on POSIXish systems, it is the value returned by**\
   **getconf CS\_PATH** **).**

  **If the -v option is given, instead of executing** *cmd***, information** **about what would be executed is given (and the same is done for** *arg1* **for special and regular built-in commands and functions,** **their names are simply printed,** **for aliases, a command that defines them is printed,** **and for commands found by searching the PATH parameter,** **the full path of the command is printed.** **If no command is be found, (i.e., the path search fails), nothing is printed** **and command exits with a non-zero status.** **The -V option is like the -v option, except it is more verbose.**

- **continue** \[*levels*\]

  **continue jumps to the beginning of the** *level***th inner most for,** **select, until, or while loop.** *level* **defaults to 1.**

- **echo** \[**-neE**\] \[*arg* ...\]

  **Prints its arguments (separated by spaces) followed by a newline, to** **standard out.** **The newline is suppressed if any of the arguments contain the backslash** **sequence \\c.** **See print command below for a list of other backslash sequences** **that are recognized.**

  **The options are provided for compatibility with BSD shell scripts:** **-n suppresses the trailing newline, -e enables backslash** **interpretation (a no-op, since this is normally done), and -E which** **suppresses backslash interpretation.**

- **eval** *command ...*

  **The arguments are concatenated (with spaces between them) to form** **a single string which the shell then parses and executes** **in the current environment.**

- **exec** \[*command* \[*arg* ...\]\]

  **The command is executed without forking, replacing the shell process.**

  **If no arguments are given, any IO redirection is permanent and the shell** **is not replaced.** **Any file descriptors greater than 2 which are opened or** *dup***(2)-ed** **in this way are not made available to other executed commands (i.e.,** **commands that are not built-in to the shell).**

- **exit** \[*status*\]

  **The shell exits with the specified exit status.** **If** *status* **is not specified, the exit status is the current** **value of the ? parameter.**

- **export** \[**-p**\] \[*parameter*\[**=***value*\]\] ...

  **Sets the export attribute of the named parameters.** **Exported parameters are passed in the environment to executed commands.** **If values are specified, the named parameters also assigned.**

  **If no parameters are specified, the names of all parameters with the export** **attribute are printed one per line, unless the -p option is used,** **in which case export commands defining all exported** **parameters, including their values, are printed.**

- **false**

  **A command that exits with a non-zero status.**

- **fc** \[**-e** *editor* \| **-l** \[**-n**\]\] \[**-r**\] \[*first* \[*last*\]\]

  *first* **and** *last* **select commands from the history.** **Commands can be selected by** **history number, or a string specifying the most recent command starting** **with that string.  The -l option lists the command on stdout,** **and -n inhibits the default command numbers.  The -r** **option reverses the order of the list.  Without -l, the selected** **commands are edited by the editor specified with the -e** **option, or if no -e is specified, the editor specified by the** **FCEDIT parameter (if this parameter is not set, /bin/ed is used),** **and then executed by the shell.**

- **fc** \[**-e -** \| **-s**\] \[**-g**\] \[*old***=***new*\] \[*prefix*\]

  **Re-execute the selected command (the previous command by default) after** **performing the optional substitution of** *old* **with** *new***.  If** **-g is specified, all occurrences of** *old* **are replaced with** *new***.  This command is usually accessed with the predefined alias** **r='fc -e -'.**

- **fg** \[*job* ...\]

  **Resume the specified job(s) in the foreground.** **If no jobs are specified, %+ is assumed.** **This command is only available on systems which support job control.** **See Job Control below for more information.**

- **getopts** *optstring* *name* \[*arg* ...\]

  **getopts is used by shell procedures to parse the specified arguments** **(or positional parameters, if no arguments are given) and to check for legal** **options.** *optstring* **contains the option letters that** **getopts is to recognize.  If a letter is followed by a colon, the** **option is expected to have an argument.** **Arguments containing options must all start with either a - or** **a +, options that do not take arguments may be grouped in a single** **argument.** **If an option takes an argument and the option character is not the last** **character of the argument it is found in, the remainder of the argument** **is taken to be the option's argument, otherwise, the next argument is** **the option's argument.**

  **Each time getopts is invoked, it places the next option in** **the shell parameter** *name* **and the index of the next argument to be** **processed in the shell parameter OPTIND.** **If the option was introduced with a +, the option placed in** *name* **is prefixed with a +.** **When an option requires an argument, getopts places it in the** **shell parameter OPTARG.** **When an illegal option or a missing option argument is** **encountered a question mark or a colon is placed in** *name* **(indicating an illegal option or missing argument, respectively)** **and OPTARG is set to the option character that caused the problem.** **An error message is also printed to standard error if** *optstring* **does not begin with a colon.**

  **When the end of the options is encountered, getopts exits with a** **non-zero exit status.** **Options end at the first (non-option argument) argument that does not** **start with a -, or when a -- argument is encountered.**

  **Option parsing can be reset by setting OPTIND to 1 (this is done** **automatically whenever the shell or a shell procedure is invoked).**

  **Warning: Changing the value of the shell parameter OPTIND to** **a value other than 1, or parsing different sets of arguments without** **resetting OPTIND may lead to unexpected results.**

- **hash** \[**-r**\] \[*name ...*\]

  **Without arguments, any hashed executable command pathnames are listed.** **The -r option causes all hashed commands to be removed** **from the hash table.** **Each** *name* **is searched as if it where a command name and added to the** **hash table if it is an executable command.**

- **jobs** \[**-lpn**\] \[*job* ...\]

  **Display information about the specified jobs; if no jobs are specified,** **all jobs are displayed.** **The -n option causes information to be displayed only for jobs** **that have changed state since the last notification.** **If the -l option is used, the process-id of each process in a job** **is also listed.** **The -p option causes only the process group of each job to be printed.** **See Job Control below for the format of** *job* **and the displayed job.**

- **kill** \[**-s** *signame* \| **-signum** \| **-signame** \] { *job* \| *pid* \| **-***pgrp* } ...

  **Send the specified signal to the specified jobs, process ids, or process groups.** **If no signal is specified, the signal TERM is sent.** **If a job is specified, the signal is sent to the job's process group.** **See Job Control below for the format of** *job***.**

- **kill -l** \[*exit-status* ...\]

  **Print the name of the signal that killed a process which exited with** **the specified** *exit-status***es.** **If no arguments are specified, a list of all the signals, their numbers and** **a short description of them are printed.**

- **let** \[*expression* ...\]

  **Each expression is evaluated, see Arithmetic Expressions above.** **If all expressions are successfully evaluated, the exit status** **is 0 (1) if the last expression evaluated to non-zero (zero).** **If an error occurs during the parsing or evaluation of an expression,** **the exit status is greater than 1.** **Since expressions may need to be** **quoted, ((** *expr* **)) is syntactic sugar for let** **"***expr***".**

- **print** \[**-nprsu***n* **\| -R \[-en\]\] \[***argument ...***\]**

  **Print prints its arguments on the standard output, separated by** **spaces, and terminated with a newline.  The -n option suppresses** **the newline.  By default, certain C escapes are translated.  These** **include \\b, \\f, \\n, \\r, \\t, \\v, and \\### (# is an octal digit).** **\\c is equivalent to using the -n option.  \\ expansion may be** **inhibited with the -r option.** **The -s option prints to the history file instead of standard output,** **the -u option prints to file descriptor** *n* **(***n* **defaults to 1 if omitted), and the -p option prints to the co-process** **(see Co-Processes above).**

  **The -R option is used to emulate, to some degree, the BSD echo** **command, which does not process \\ sequences unless the -e option** **is given.** **As above, the -n option suppresses the trailing newline.**

- **pwd** \[**-LP**\]

  **Print the present working directory.** **If -L option is used or if the physical option** **(see set command below) isn't set, the logical path is printed** **(i.e., the path used to cd to the current directory).** **If -P option (physical path) is used or if the physical option** **is set, the path determined from the filesystem (by following ..** **directories to the root directory) is printed.**

- **read** \[**-prsu***n*\] \[*parameter ...*\]

  **Reads a line of input from standard input, separate the line into fields using** **the IFS parameter (see Substitution above), and assign each field to the** **specified parameters.** **If there are more parameters than fields, the extra parameters are set to null,** **or alternatively, if there are more fields than parameters, the last parameter** **is assigned the remaining fields (inclusive of any separating spaces).** **If no parameters are specified, the REPLY parameter is used.** **If the input line ends in a backslash and the -r option was not used, the** **backslash and newline are stripped and more input is read.** **If no input is read, read exits with a non-zero status.**

  **A prompt, which is printed to standard error before any input is read, may be** **specified by appending and question mark and the prompt to the** **first parameter (e.g., read nfoo?'number of foos: ').**

  **The -u***n* **and -p options cause input to be read** **from file descriptor** *n* **or the current co-process, respectively.** **If the -s option is used, input is saved to the history file.**

- **readonly** \[**-p**\] \[*parameter*\[**=***value*\]\] ...

  **Sets the readonly attribute of the named parameters.  If values are given,** **parameters are set to them before setting the attribute.** **Once a parameter is made readonly, it cannot be unset and its value cannot** **be changed.**

  **If no parameters are specified, the names of all parameters with the readonly** **attribute are printed one per line, unless the -p option is used,** **in which case readonly commands defining all readonly** **parameters, including their values, are printed.**

- **return** \[*status*\]

  **Returns from a function or . script, with exit status** *status***.** **If no** *status* **is given, the exit status of the last executed command** **is used.** **If used outside of a function or . script, it has the same effect** **as exit.** **Note that pdksh treats both profile and $ENV files as . scripts,** **while the original Korn shell only treats profiles as . scripts.**

- **set** \[**±abCefhkmnpsuvxX**\] \[**±o** \[*option*\]\] \[**±A** *name*\] \[**--**\] \[*arg* ...\]

  **Set (-) or clear (+) a shell option:**

  | | | |
  | --- | --- | --- |
  | **-A** |  | Sets the elements of the array parameter *name* to *arg* ...; If **-A** is used, the array is reset (i.e., emptied) first; if **+A** is used, the first N elements are set (where N is the number of *arg*s), the rest are left untouched. |
  | **-a** | **allexport** | all new parameters are created with the export attribute |
  | **-b** | **notify** | Print job notification messages asynchronously, instead of just before the prompt. Only used if job control is enabled (**-m**). |
  | **-C** | **noclobber** | Prevent **\>** redirection from overwriting existing files (**\>\|** must be used to force an overwrite). |
  | **-e** | **errexit** | Exit (after executing the **ERR** trap) as soon as an error occurs or a command fails (i.e., exits with a non-zero status). This does not apply to commands whose exit status is explicitly tested by a shell construct such as **if**, **until**, **while**, **&&** or **\|\|** statements. |
  | **-f** | **noglob** | Do not expand file name patterns. |
  | **-f** | **nohup** | Do not kill running jobs with a **HUP** signal when a login shell exists. Currently set by default, but this will change in the future to be compatible with the original Korn shell (which doesn't have this option, but does send the **HUP** signal). |
  | **-h** | **trackall** | Create tracked aliases for all executed commands (see Aliases above). On by default for non-interactive shells. |
  | **-i** | **interactive** | Enable interactive mode - this can only be set/unset when the shell is invoked. |
  | **-k** | **keyword** | Parameter assignments are recognized anywhere in a command. |
  | **-l** | **login** | The shell is a login shell - this can only be set/unset when the shell is invoked (see Shell Startup above). |
  | **-m** | **monitor** | Enable job control (default for interactive shells). |
  | **-n** | **noexec** | Do not execute any commands - useful for checking the syntax of scripts (ignored if interactive). |
  | **-p** | **privileged** | Set automatically if, when the shell starts, the read uid or gid does not match the effective uid or gid, respectively. See Shell Startup above for a description of what this means. |
  | **-r** | **restricted** | Enable restricted mode — this option can only be used when the shell is invoked. See Shell Startup above for a description of what this means. |
  | **-s** |  |  |
  | **-s** | **stdin** | If used when the shell is invoked, commands are read from standard input. Set automatically if the shell is invoked with no arguments. When **-s** is used in the **set** command, it causes the specified arguments to be sorted before assigning them to the positional parameters (or to array *name*, if **-A** is used). |
  | **-u** | **nounset** | Referencing of an unset parameter is treated as an error, unless one of the **-**, **+** or **=** modifiers is used. |
  | **-v** | **verbose** | Write shell input to standard error as it is read. |
  | **-x** | **xtrace** | Print commands and parameter assignments when they are executed, preceded by the value of **PS4**. |
  | **-X** | **markdirs** | Mark directories with a trailing **/** during file name generation. |
  |  | **bgnice** | Background jobs are run with lower priority. |
  |  | **braceexpand** | Enable brace expansion (aka, alternation). |
  |  | **emacs** | Enable BRL emacs-like command line editing (interactive shells only); see Emacs Interactive Input Line Editing. |
  |  | **gmacs** | Enable gmacs-like (Gosling emacs) command line editing (interactive shells only); currently identical to emacs editing except that transpose (^T) acts slightly differently. |
  |  | **ignoreeof** | The shell will not exit on when end-of-file is read, **exit** must be used. |
  |  | **nolog** | No effect - in the original Korn shell, this prevents function definitions from being stored in the history file. |
  |  | **physical** | Causes the **cd** and **pwd** commands to use \`physical' (i.e., the filesystem's) **..** directories instead of \`logical' directories (i.e., the shell handles **..**, which allows the user to be obliveous of symlink links to directories). Clear by default. Note that setting this option does not effect the current value of the **PWD** parameter; only the **cd** command changes **PWD**. See the **cd** and **pwd** commands above for more details. |
  |  | **posix** | Enable posix mode. See POSIX Mode above. |
  |  | **vi** | Enable vi-like command line editing (interactive shells only). |
  |  | **viraw** | No effect - in the original Korn shell, unless viraw was set, the vi command line mode would let the tty driver do the work until ESC (^\[) was entered. pdksh is always in viraw mode. |
  |  | **vi-show8** | Prefix characters with the eighth bit set with \`M-'. If this option is not set, characters in the range 128-160 are printed as is, which may cause problems. |
  |  | **vi-tabcomplete** | In vi command line editing, do file name completion when tab (^I) is entered in insert mode. |

  **These options can also be used upon invocation of the shell.  The current** **set of options can be found in the parameter -.  Remaining** **arguments, if any, are positional parameters and are assigned, in order, to the** **positional parameters (i.e., 1, 2, etc.).** **If options are ended with -- and there are no remaining arguments,** **all positional parameters are cleared.** **If no options or arguments are given, then the values of all names are printed.** **For unknown historical reasons, a lone - option is treated specially:** **it clears both the -x and -v options.**

- **shift** \[*number*\]

  **The positional parameters** *number***+1,** *number***+2 etc. are renamed** **to 1, 2, etc.** *number* **defaults to 1.**

- **test** *expression*

  - **\[** *expression* **\]**

  **test evaluates the** *expression* **and returns zero status if** **true, and 1 status if false and greater than 1 if there was an error.** **It is normally used as the** **condition command of if and while statements.** **The following basic expressions are available:**

  | | |
  | --- | --- |
  | ***str*** | *str* has non-zero length. Note that there is the potential for problems if *str* turns out to be an operator (e.g., **-r**) - it is generally better to use a test like **\[ X"***str***" != X \]** instead (double quotes are used in case *str* contains spaces or file globing characters). |
  | **-r *file*** | *file* exists and is readable |
  | **-w *file*** | *file* exists and is writable |
  | **-x *file*** | *file* exists and is executable |
  | **-a *file*** | *file* exists |
  | **-e *file*** | *file* exists |
  | **-f *file*** | *file* is a regular file |
  | **-d *file*** | *file* is a directory |
  | **-c *file*** | *file* is a character special device |
  | **-b *file*** | *file* is a block special device |
  | **-p *file*** | *file* is a named pipe |
  | **-u *file*** | *file*'s mode has setuid bit set |
  | **-g *file*** | *file*'s mode has setgid bit set |
  | **-k *file*** | *file*'s mode has sticky bit set |
  | **-s *file*** | *file* is not empty |
  | **-O *file*** | *file*'s owner is the shell's effective user-ID |
  | **-G *file*** | *file*'s group is the shell's effective group-ID |
  | **-h *file*** | *file* is a symbolic link |
  | **-H *file*** | *file* is a context dependent directory (only useful on HP-UX) |
  | **-L *file*** | *file* is a symbolic link |
  | **-S *file*** | *file* is a socket |
  | **-o *option*** | shell *option* is set (see **set** command above for list of options). As a non-standard extension, if the option starts with a **!**, the test is negated; the test always fails if option doesn't exist (thus **\[ -o** *foo* **-o -o** *foo* **\]** returns true if and only if option *foo* exists). |
  | ***file* -nt *file*** | first *file* is newer than second *file* |
  | ***file* -ot *file*** | first *file* is older than second *file* |
  | ***file* -ef *file*** | first *file* is the same file as second *file* |
  | **-t \[*fd*\]** | file descriptor is a tty device. Default value of *fd* is 1. |
  | ***string*** | *string* is not empty |
  | **-z *string*** | *string* is empty |
  | **-n *string*** | *string* is not empty |
  | ***string* = *string*** | strings are equal |
  | ***string* != *string*** | strings are not equal |
  | ***number* -eq *number*** | numbers compare equal |
  | ***number* -ne *number*** | numbers compare not equal |
  | ***number* -ge *number*** | numbers compare greater than or equal |
  | ***number* -gt *number*** | numbers compare greater than |
  | ***number* -le *number*** | numbers compare less than or equal |
  | ***number* -lt *number*** | numbers compare less than |

  **The above basic expressions, in which unary operators have precedence over** **binary operators, may be combined with the following operators** **(listed in increasing order of precedence):**

  | | |
  | --- | --- |
  | ***expr* -o *expr*** | logical or |
  | ***expr* -a *expr*** | logical and |
  | **! *expr*** | logical not |
  | **( *expr* )** | grouping |

  **Note that some special rules are applied (courtesy of POSIX) if the** **number of arguments to test or \[ ... \] is less than** **five: if leading ! arguments can be stripped such that only one** **argument remains then a string length test is performed (again, even if** **the argument is a unary operator);** **if leading ! arguments can be stripped such that three** **arguments remain and the second argument is a binary operator, then the** **binary operation is performed (even if first argument is a unary** **operator, including an unstripped !).**

  **Note: A common mistake is to use if \[ $foo = bar \] which** **fails if parameter foo is null or unset, if it has embedded spaces** **(i.e., IFS characters), or if it is a unary operator like ! or** **-n.  Use tests like if \[ "X$foo" = Xbar \] instead.**

- **times**

  **Print the accumulated user and system times used by the shell and by** **processes which have exited that the shell started.**

- **trap** \[*handler* *signal ...*\]

  **Sets trap handler that is to be executed when any of the specified signals** **are received.** **Handler is either a null string, indicating the signals are to** **be ignored, a minus (-), indicating that the default action is to** **be taken for the signals (see signal(2 or 3)), or a string containing shell** **commands to be evaluated and executed at the first opportunity (i.e., when the** **current command completes, or before printing the next PS1 prompt) after** **receipt of one of the signals.** **Signal is the name of a signal (e.g., PIPE or ALRM) or the number** **of the signal (see kill -l command above).** **There are two special signals: EXIT (also known as 0), which** **is executed when the shell is about to exit, and ERR which is** **executed after an error occurs (an error is something that would cause** **the shell to exit if the -e or errexit option were set —** **see set command above).** **EXIT handlers are executed in the environment of the last executed** **command.** **Note that for non-interactive shells, the trap handler cannot be changed for** **signals that were ignored when the shell started.**

  **With no arguments, trap lists, as a series of trap commands,** **the current state of the traps that have been set since the shell started.**

  **The original Korn shell's DEBUG trap and the handling of ERR and** **EXIT traps in functions are not yet implemented.**

- **true**

  **A command that exits with a zero value.**

- **typeset** \[\[±Ulrtux\] \[**-L**\[*n*\]\] \[**-R**\[*n*\]\] \[**-Z**\[*n*\]\] \[**-i**\[*n*\]\] \| **-f** \[**-tux**\]\] \[*name*\[**=***value*\] ...\]

  **Display or set parameter attributes.** **With no** *name* **arguments, parameter attributes are displayed: if no options** **arg used, the current attributes of all parameters are printed as typeset** **commands; if an option is given (or - with no option letter)** **all parameters and their values with the specified attributes are printed;** **if options are introduced with +, parameter values are not printed.**

  **If** *name* **arguments are given, the attributes of the named parameters** **are set (-) or cleared (+).** **Values for parameters may optionally be specified.** **If typeset is used inside a function, any newly created parameters are local** **to the function.**

  **When -f is used, typeset operates on the attributes of functions.** **As with parameters, if no** *name***s are given, functions are listed** **with their values (i.e., definitions) unless options are introduced with** **+, in which case only the function names are reported.**

  | | |
  | --- | --- |
  | **-L*n*** | Left justify attribute: *n* specifies the field width. If *n* is not specified, the current width of a parameter (or the width of its first assigned value) is used. Leading white space (and zeros, if used with the **-Z** option) is stripped. If necessary, values are either truncated or space padded to fit the field width. |
  | **-R*n*** | Right justify attribute: *n* specifies the field width. If *n* is not specified, the current width of a parameter (or the width of its first assigned value) is used. Trailing white space are stripped. If necessary, values are either stripped of leading characters or space padded to make them fit the field width. |
  | **-Z*n*** | Zero fill attribute: if not combined with **-L**, this is the same as **-R**, except zero padding is used instead of space padding. |
  | **-i*n*** | integer attribute: *n* specifies the base to use when displaying the integer (if not specified, the base given in the first assignment is used). Parameters with this attribute may be assigned values containing arithmetic expressions. |
  | **-U** | unsigned integer attribute: integers are printed as unsigned values (only useful when combined with the **-i** option). This option is not in the original Korn shell. |
  | **-f** | Function mode: display or set functions and their attributes, instead of parameters. |
  | **-l** | Lower case attribute: all upper case characters in values are converted to lower case. (In the original Korn shell, this parameter meant \`long integer' when used with the **-i** option). |
  | **-r** | Readonly attribute: parameters with the this attribute may not be assigned to or unset. Once this attribute is set, it can not be turned off. |
  | **-t** | Tag attribute: has no meaning to the shell; provided for application use. For functions, **-t** is the trace attribute. When functions with the trace attribute are executed, the **xtrace** (**-x**) shell option is temporarily turned on. |
  | **-u** | Upper case attribute: all lower case characters in values are converted to upper case. (In the original Korn shell, this parameter meant \`unsigned integer' when used with the **-i** option, which meant upper case letters would never be used for bases greater than 10. See the **-U** option). For functions, **-u** is the undefined attribute. See Functions above for the implications of this. |
  | **-x** | Export attribute: parameters (or functions) are placed in the environment of any executed commands. Exported functions are not implemented yet. |

- **ulimit** \[**-acdfHmnsStvw**\] \[*value*\]

  **Display or set process limits.** **If no options are used, the file size limit (-f) is assumed.** **value, if specified, may be either be an arithmetic expression or the** **word unlimited.** **The limits affect the shell and any processes created by the shell after** **a limit is imposed.** **Note that some systems may not allow limits to be increased once they** **are set.** **Also note that the types of limits available are system dependent - some** **systems have only the -f limit.**

  - **-a**

    **Displays all limits.**

  - **-H**

    **Set the hard limit only (default is to set both hard and soft limits).**

  - **-S**

    **Set the soft limit only (default is to set both hard and soft limits).**

  - **-c**

    **Impose a size limit of** *n* **blocks on the size of core dumps.**

  - **-d**

    **Impose a size limit of** *n* **kbytes on the size of the data area.**

  - **-f**

    **Impose a size limit of** *n* **blocks on files written by the shell and** **its child processes (files of any size may be read).**

  - **-m**

    **Impose a limit of** *n* **kbytes on the amount of physical memory used.**

  - **-n**

    **Impose a limit of** *n* **file descriptors that can be open at once.**

  - **-s**

    **Impose a size limit of** *n* **kbytes on the size of the stack area.**

  - **-t**

    **Impose a time limit of** *n* **seconds to be used by each process.**

  - **-v**

    **Impose a limit of** *n* **kbytes on the amount of virtual memory used;** **on some systems this is the maximum allowable virtual address (in bytes,** **not kbytes).**

  - **-w**

    **Impose a limit of** *n* **kbytes on the amount of swap space used.**

  **As far as ulimit is concerned, a block is 512 bytes.**

- **umask** \[**-S**\] \[*mask*\]

  **Display or set the file permission creation mask, or umask (see** *umask***(2)).** **If the -S option is used, the mask displayed or set is symbolic,** **otherwise it is an octal number.**

  **Symbolic masks are like those used by** *chmod***(1):**\
   **\[ugoa\]{{=+-}{rwx}\*}+\[,...\]** **in which the first group of characters is the** *who* **part, the second** **group is the** *op* **part, and the last group is the** *perm* **part.** **The** *who* **part specifies which part of the umask is to be modified.** **The letters mean:**

  - **u**

    **the user permissions**

  - **g**

    **the group permissions**

  - **o**

    **the other permissions (non-user, non-group)**

  - **a**

    **all permissions (user, group and other)**

  **The** *op* **part indicates how the** *who* **permissions are to be modified:**

  - **=**

    **set**

  - **+**

    **added to**

  - **-**

    **removed from**

  **The** *perm* **part specifies which permissions are to be set, added or removed:**

  - **r**

    **read permission**

  - **w**

    **write permission**

  - **x**

    **execute permission**

  **When symbolic masks are used, they describe what permissions may** **be made available (as opposed to octal masks in which a set bit means** **the corresponding bit is to be cleared).** **Example: \`ug=rwx,o=' sets the mask so files will not be readable, writable** **or executable by \`others', and is equivalent (on most systems) to the octal** **mask \`07'.**

- **unalias** \[**-adt**\] \[*name1* ...\]

  **The aliases for the given names are removed.** **If the -a option is used, all aliases are removed.** **If the -t or -d options are used, the indicated operations** **are carried out on tracked or directory aliases, respectively.**

- **unset** \[**-fv**\] *parameter* ...

  **Unset the named parameters (-v, the default) or functions (-f).**

- **wait** \[*job*\]

  **Wait for the specified job(s) to finish.** **The exit status of wait is that of the last specified job:** **if the last job is killed by a signal, the exit status is 128 + the** **number of the signal (see kill -l** *exit-status* **above); if the last** **specified job can't be found (because it never existed, or had already** **finished), the exit status of wait is 127.** **See Job Control below for the format of** *job***.** **Wait will return if a signal for which a trap has been set is received,** **or if a HUP, INT or QUIT signal is received.**

  **If no jobs are specified, wait waits for all currently running jobs** **(if any) to finish and exits with a zero status.** **If job monitoring is enabled, the completion status of jobs is** **printed (this is not the case when jobs are explicitly specified).**

- **whence** \[**-pv**\] \[name ...\]

  **For each name, the type of command is listed (reserved word, built-in, alias,** **function, tracked alias or executable).** **If the -p option is used, a path search done even if** *name* **is a reserved word, alias, etc.** **Without the -v option, whence is similar to command -v** **except that whence will find reserved words and won't print aliases** **as alias commands;** **with the -v option, whence is the same as command -V.** **Note that for whence, the -p option does not affect the search** **path used, as it does for command.** **If the type of one or more of the names could not be determined, the** **exit status is non-zero.**

### Job Control

**Job control refers to the shell's ability to monitor and control jobs,** **which are processes or groups of processes created for commands or pipelines.** **At a minimum, the shell keeps track of the status of the background** **(i.e., asynchronous) jobs that currently exist; this information can be** **displayed using the jobs command.** **If job control is fully enabled (using set -m or** **set -o monitor), as it is for interactive shells,** **the processes of a job are placed in their own process group,** **foreground jobs can be stopped by typing the suspend character from the** **terminal (normally ^Z),** **jobs can be restarted in either the foreground** **or background, using the fg and bg commands, respectively,** **and the state of the terminal is saved or restored when a foreground** **job is stopped or restarted, respectively.**

**Note that only commands that create processes (e.g., asynchronous commands,** **subshell commands, and non-built-in, non-function commands) can be** **stopped; commands like read cannot be.**

**When a job is created, it is assigned a job-number.** **For interactive shells, this number is printed inside \[..\],** **followed by the process-ids of the processes in the job when an asynchronous** **command is run.** **A job may be referred to in bg, fg, jobs, kill and** **wait commands either by the process id of the last process in the** **command pipeline (as stored in the $! parameter) or by prefixing the** **job-number with a percent sign (%).** **Other percent sequences can also be used to refer to jobs:**

| | |
| --- | --- |
| **%+** | The most recently stopped job, or, if there are no stopped jobs, the oldest running job. |
| **%%, %** | Same as **%+**. |
| **%-** | The job that would be the **%+** job, if the later did not exist. |
| **%*n*** | The job with job-number *n*. |
| **%?*string*** | The job containing the string *string* (an error occurs if multiple jobs are matched). |
| **%*string*** | The job starting with string *string* (an error occurs if multiple jobs are matched). |

**When a job changes state (e.g., a background job finishes or foreground** **job is stopped), the shell prints the following status information:**\
 **\[***number***\]** *flag status command* **where**

- *number*

  **is the job-number of the job.**

- *flag*

  **is + or - if the job is the %+ or %- job,** **respectively, or space if it is neither.**

- *status*

  **indicates the current state of the job and can be**

  - **Running**

    **the job has neither stopped or exited (note that running does not** **necessarily mean consuming CPU time — the process could be blocked waiting** **for some event).**

  - **Done** \[**(***number***)**\]

    **the job exited.** *number* **is the exit status of the job, which is** **omitted if the status is zero.**

  - **Stopped** \[**(***signal***)**\]

    **the job was stopped by the indicated** *signal* **(if no signal is given,** **the job was stopped by SIGTSTP).**

  - *signal-description* \[**(core dumped)**\]

    **the job was killed by a signal (e.g., Memory fault, Hangup, etc. — use** **kill -l for a list of signal descriptions).** **The (core dumped) message indicates the process created a core file.**

- *command*

  **is the command that created the process.** **If there are multiple processes in the job, then each process will** **have a line showing its** *command* **and possibly its** *status***,** **if it is different from the status of the previous process.**

**When an attempt is made to exit the shell while there are jobs in** **the stopped state, the shell warns the user that there are stopped jobs** **and does not exit.** **If another attempt is immediately made to exit the shell, the stopped** **jobs are sent a HUP signal and the shell exits.** **Similarly, if the nohup option is not set and there are running** **jobs when an attempt is made to exit a login shell, the shell warns the** **user and does not exit.** **If another attempt is immediately made to exit the shell, the running** **jobs are sent a HUP signal and the shell exits.**

### Emacs Interactive Input Line Editing

**When the emacs option is set, interactive input line editing is** **enabled.  Warning: This mode is slightly different from the emacs** **mode in the original Korn shell and the 8th bit is stripped in emacs mode.** **In this mode various editing commands (typically bound to one or more** **control characters) cause immediate actions without waiting for a** **new-line.  Several editing commands are bound to particular control** **characters when the shell is invoked; these bindings can be changed** **using the following commands:**

- **bind**

  **The current bindings are listed.**

- **bind** *string***=**\[*editing-command*\]

  **The specified editing command is bound to the given string, which** **should consist of a control character (which may be written using caret** **notation ^***X***), optionally preceded by one of the two prefix** **characters.  Future input of the** *string* **will cause the editing** **command to be immediately invoked.  Note that although only two prefix** **characters (usually ESC and ^X) are supported, some multi-character** **sequences can be supported.  The following binds the arrow keys on** **an ANSI terminal, or xterm (these are in the default bindings).  Of course** **some escape sequences won't work out quite this nicely:**

  **bind '^\[\['=prefix-2**\
   **bind '^XA'=up-history**\
   **bind '^XB'=down-history**\
   **bind '^XC'=forward-char**\
   **bind '^XD'=backward-char**

- **bind -l**

  **Lists the names of the functions to which keys may be bound.**

- **bind -m** *string***=**\[*substitute*\]

  **The specified input** *string* **will afterwards be immediately** **replaced by the given** *substitute* **string, which may contain** **editing commands.**

**The following is a list of editing commands available.** **Each description starts with the name of the command,** **a** *n***, if the command can be prefixed with a count,** **and any keys the command is bound to by default (written using** **caret notation, e.g., ASCII ESC character is written as ^\[).** **A count prefix for a command is entered using the sequence** **^\[***n***, where** *n* **is a sequence of 1 or more digits;** **unless otherwise specified, if a count is omitted, it defaults to 1.** **Note that editing command names are** **used only with the bind command.  Furthermore, many editing** **commands are useful only on terminals with a visible cursor.  The** **default bindings were chosen to resemble corresponding EMACS key** **bindings.  The users tty characters (e.g., ERASE) are bound to** **reasonable substitutes and override the default bindings.**

- **abort ^G**

  **Useful as a response to a request for a search-history pattern in** **order to abort the search.**

- **auto-insert** *n*

  **Simply causes the character to appear as literal input.  Most ordinary** **characters are bound to this.**

- **backward-char** *n* **^B**

  **Moves the cursor backward** *n* **characters.**

- **backward-word** *n* **^\[B**

  **Moves the cursor backward to the beginning of a word; words consist** **of alphanumerics, underscore (\_) and dollar ($).**

- **beginning-of-history ^\[\<**

  **Moves to the beginning of the history.**

- **beginning-of-line ^A**

  **Moves the cursor to the beginning of the edited input line.**

- **capitalize-word** *n* **^\[c**, **^\[C**

  **Uppercase the first character in the next** *n* **words,** **leaving the cursor past the end of the last word.**

- **complete ^\[^\[**

  **Automatically completes as much as is unique of the hashed command name** **or the file name containing the cursor.  If the entire remaining command** **or file name is unique a space is printed after its completion, unless** **it is a directory name in which case / is appended.  If there is** **no hashed command or file name with the current partial word as its** **prefix, a bell character is output (usually causing a audio beep).**

- **complete-command ^X^\[**

  **Automatically completes as much as is unique of the hashed command name** **having the partial word up to the cursor as its prefix, as in the** **complete command described above.  Only command and function names** **seen since the last hash -r command are available for** **completion; the hash command may be used to register additional** **names.**

- **complete-file ^\[^X**

  **Automatically completes as much as is unique of the file name having** **the partial word up to the cursor as its prefix, as in the** **complete command described above.**

- **complete-list ^\[=**

  **List the possible completions for the current word.**

- **delete-char-backward** *n* **ERASE**, **^?**, **^H**

  **Deletes** *n* **characters before the cursor.**

- **delete-char-forward** *n*

  **Deletes** *n* **characters after the cursor.**

- **delete-word-backward** *n* **^\[ERASE**, **^\[^?**, **^\[^H**, **^\[h**

  **Deletes** *n* **words before the cursor.**

- **delete-word-forward** *n* **^\[d**

  **Deletes characters after the cursor up to the end of** *n* **words.**

- **down-history** *n* **^N**

  **Scrolls the history buffer forward** *n* **lines (later).  Each input line** **originally starts just after the last entry in the history buffer, so** **down-history is not useful until either search-history or** **up-history has been performed.**

- **downcase-word** *n* **^\[L**, **^\[l**

  **Lowercases the next** *n* **words.**

- **end-of-history ^\[\>**

  **Moves to the end of the history.**

- **end-of-line ^E**

  **Moves the cursor to the end of the input line.**

- **eot ^\_**

  **Acts as an end-of-file; this is useful because edit-mode input disables** **normal terminal input canonicalization.**

- **eot-or-delete** *n* **^D**

  **Acts as eot if alone on a line; otherwise acts as delete-char-forward.**

- **error**

  **Error (ring the bell).**

- **exchange-point-and-mark ^X^X**

  **Places the cursor where the mark is, and sets the mark to where the** **cursor was.**

- **forward-char** *n* **^F**

  **Moves the cursor forward** *n* **characters.**

- **forward-word** *n* **^\[f**

  **Moves the cursor forward to the end of the** *n***th word.**

- **goto-history** *n* **^\[g**

  **Goes to history number** *n***.**

- **kill-line KILL**

  **Deletes the entire input line.**

- **kill-region ^W**

  **Deletes the input between the cursor and the mark.**

- **kill-to-eol** *n* **^K**

  **Deletes the input from the cursor to the end of the line if** *n* **is** **not specified, otherwise deletes characters between the cursor and** **column** *n***.**

- **list ^\[?**

  **Prints a sorted, columnated list of hashed command names or file names** **(if any) that can complete the partial word containing the cursor.** **Directory names have / appended to them, and executable file** **names are followed by a \*.**

- **list-command ^X?**

  **Prints a sorted, columnated list of hashed command names (if any) that** **can complete the partial word containing the cursor.**

- **list-file ^X^Y**

  **Prints a sorted, columnated list of file names (if any) that can** **complete the partial word containing the cursor.  File type indicators** **are appended as described under list above.**

- **newline ^J**, **^M**

  **Causes the current input line to be processed by the shell.  The** **current cursor position may be anywhere on the line.**

- **newline-and-next ^O**

  **Causes the current input line to be processed by the shell, and** **the next line from history becomes the current line.  This is** **only useful after an up-history or search-history.**

- **no-op QUIT**

  **This does nothing.**

- **prefix-1 ^\[**

  **Introduces a 2-character command sequence.**

- **prefix-2 ^X**

  - **prefix-2 ^\[\[**

  **Introduces a 2-character command sequence.**

- **prev-hist-word** *n* **^\[.**, **^\[\_**

  **The last (***n***th) word of the previous command is inserted at the cursor.**

- **quote ^^**

  **The following character is taken literally rather than as an editing** **command.**

- **redraw ^L**

  **Reprints the prompt string and the current input line.**

- **search-character-backward** *n* **^\[^\]**

  **Search backward in the current line for the** *n***th occurance of the** **next character typed.**

- **search-character-forward** *n* **^\]**

  **Search forward in the current line for the** *n***th occurance of the** **next character typed.**

- **search-history ^R**

  **Enter incremental search mode.  The internal history list is searched** **backwards for commands matching the input.  An initial ^ in the** **search string anchors the search.  The abort key will leave search mode.** **Other commands will be executed after leaving search mode.  Successive** **search-history commands continue searching backward to the next** **previous occurrence of the pattern.  The history buffer retains only a** **finite number of lines; the oldest are discarded as necessary.**

- **set-mark-command ^\[**\<space\>

  **Set the mark at the cursor position.**

- **stuff**

  **On systems supporting it, pushes the bound character back onto the** **terminal input where it may receive special processing by the terminal** **handler.  This is useful for the BRL ^T mini-systat feature, for** **example.**

- **stuff-reset**

  **Acts like stuff, then aborts input the same as an interrupt.**

- **transpose-chars ^T**

  **If at the end of line, or if the gmacs option is set,**  **this exchanges the two previous characters; otherwise, it** **exchanges the previous and current characters and moves the cursor** **one character to the right.**

- **up-history** *n* **^P**

  **Scrolls the history buffer backward** *n* **lines (earlier).**

- **upcase-word** *n* **^\[U**, **^\[u**

  **Uppercases the next** *n* **words.**

- **version ^V**

  **Display the version of ksh.  The current edit buffer is restored as soon** **as any key is pressed (the key is then processed, unless it is a space).**

- **yank ^Y**

  **Inserts the most recently killed text string at the current cursor position.**

- **yank-pop ^\[y**

  **Immediately after a yank, replaces the inserted text string with** **the next previous killed text string.**

### Vi Interactive Input Line Editing

**The vi command line editor in ksh has basically the same commands as the** **vi editor (see** *vi***(1)), with the following exceptions:**

- •

  **you start out in insert mode,**

- •

  **there are file name completion commands (=, \\, \*, ^X,** **^E, ^F and, optionally, \<tab\>),**

- •

  **the \_ command is different (in ksh it is the last argument command,** **in vi it goes to the start of the current line),**

- •

  **the / and G commands move in the opposite direction as the j** **command**

- •

  **and commands which don't make sense in a single line editor are not available** **(e.g., screen movement commands, ex : commands, etc.).**

**Note that the ^X stands for control-X; also \<esc\>, \<space\>** **and \<tab\> are used for escape, space and tab, respectively (no kidding).**

**Like vi, there are two modes: insert mode and command mode.** **In insert mode, most characters are simply put in the buffer at the** **current cursor position as they are typed, however, some characters** **are treated specially.** **In particular, the following characters are taken from current tty settings** **(see** *stty***(1)) and have their usual meaning (normal values are in** **parentheses):** **kill (^U), erase (^?), werase (^W), eof (^D),** **intr (^C) and quit (^\\).** **In addition to the above, the following characters are also treated** **specially in insert mode:**

| | |
| --- | --- |
| **^H** | erases previous character |
| **^V** | literal next: the next character typed is not treated specially (can be used to insert the characters being described here) |
| **^J ^M** | end of line: the current line is read, parsed and executed by the shell |
| **\<esc\>** | puts the editor in command mode (see below) |
| **^E** | file name enumeration (see below) |
| **^F** | file name completion (see below) |
| **^X** | file name expansion (see below) |
| **\<tab\>** | optional file name completion (see below), enabled with **set -o vi-tabcomplete** |

**If a line is longer that the screen width (see COLUMNS parameter),** **a \>, + or \< character is displayed in the last column** **indicating that there are more characters after, before and after, or** **before the current position, respectively.** **The line is scrolled horizontally as necessary.**

**In command mode, each character is interpreted as a command.** **Characters that don't correspond to commands, are illegal combinations of** **commands or are commands that can't be carried out all cause beeps.** **In the following command descriptions, a** *n* **indicates the** **command may be prefixed by a number (e.g., 10l moves right 10** **characters); if no number prefix is used,** *n* **is assumed to be 1** **unless otherwise specified.** **The term \`current position' refers to the position between the cursor** **and the character preceding the cursor.** **A \`word' is a sequence of letters, digits and underscore characters or a** **sequence of non-letter, non-digit, non-underscore, non-white-space characters** **(e.g., ab2\*&^ contains two words) and a \`big-word' is a sequence of** **non-white-space characters.**

- Special ksh vi commands

  **The following commands are not in, or are different from, the normal vi file** **editor:**

  - *n***\_**

    **insert a space followed by the** *n***th big-word from the last command in the** **history at the current position and enter insert mode; if** *n* **is not** **specified, the last word is inserted.**

  - **#**

    **insert the comment character (#) at the start of the current line and** **return the line to the shell (equivalent to I#^J).**

  - *n***g**

    **like G, except if** *n* **is not specified, it goes to the most recent**  **remembered line.**

  - *n***v**

    **edit line** *n* **using the vi editor;**  **if** *n* **is not specified, the current line is edited.** **The actual command executed is** **\`fc -e ${VISUAL:-${EDITOR:-vi}}** *n***'.**

  - **\*** and **^X**

    **file name expansion: replace the current big-word with the words obtained by** **appending a \* to it and doing file name expansion.  After expansion, the** **cursor is placed just past the last word and the editor is in insert mode.**

  - **\\** and **^F**

    **file name completion: replace the current big-word with the longest unique** **match obtained after performing file name expansion.**

  - **^V**

    **display the version of pdksh; it is displayed until another key is pressed** **(this key is ignored).**

  - **=** and **^E**

    **file name enumeration: list all the files that match the current big-word.**

  - **@***c*

    **macro expansion: execute the commands found in the alias \_***c***.**

- Intra-line movement commands

  - *n***h** and *n***^H**

    **move left** *n* **characters.**

  - *n***l** and *n***\<space\>**

    **move right** *n* **characters.**

  - **0**

    **move to column 0.**

  - **^**

    **move to the first non white-space character.**

  - *n***\|**

    **move to column** *n***.**

  - **$**

    **move to the last character.**

  - *n***b**

    **move back** *n* **words.**

  - *n***B**

    **move back** *n* **big-words.**

  - *n***e**

    **move forward to the end the word,** *n* **times.**

  - *n***E**

    **move forward to the end the big-word,** *n* **times.**

  - *n***w**

    **move forward** *n* **words.**

  - *n***W**

    **move forward** *n* **big-words.**

  - **%**

    **find match: the editor looks forward for the nearest parenthesis,** **bracket or brace and then moves the to the matching parenthesis, bracket or** **brace.**

  - *n***f***c*

    **move forward to the** *n***th occurrence of the character** *c***.**

  - *n***F***c*

    **move backward to the** *n***th occurrence of the character** *c***.**

  - *n***t***c*

    **move forward to just before the** *n***th occurrence of the character** *c***.**

  - *n***T***c*

    **move backward to just before the** *n***th occurrence of the character** *c***.**

  - *n***;**

    **repeats the last f, F, t or T command.**

  - *n***,**

    **repeats the last f, F, t or T command, but moves** **in the opposite direction.**

- Inter-line movement commands

  - *n***j** and *n***+** and *n***^N**

    **move to the** *n***th next line in the history.**

  - *n***k** and *n***-** and *n***^P**

    **move to the** *n***th previous line in the history.**

  - *n***G**

    **move to line** *n* **in the history; if** *n* **is not specified, the** **number first remembered line is used.**

  - *n***g**

    **like G, except if** *n* **is not specified, it goes to the most recent**  **remembered line.**

  - *n***/***string*

    **search backward through the history for the** *n***th line containing** *string***; if** *string* **starts with ^, the remainder of the** **string must appear at the start of the history line for it to match.**

  - *n***?***string*

    **same as /, except it searches forward through the history.**

  - *n***n**

    **search for the** *n***th occurrence of the last search string; the** **direction of the search is the same as the last search.**

  - *n***N**

    **search for the** *n***th occurrence of the last search string; the** **direction of the search is the opposite of the last search.**

- Edit commands

  - *n***a**

    **append text** *n* **times: goes into insert mode just after the current** **position.** **The append is only replicated if command mode is re-entered (i.e., \<esc\> is** **used).**

  - *n***A**

    **same as a, except it appends at the end of the line.**

  - *n***i**

    **insert text** *n* **times: goes into insert mode at the current** **position.** **The insertion is only replicated if command mode is re-entered (i.e., \<esc\> is** **used).**

  - *n***I**

    **same as i, except the insertion is done just before the first non-blank** **character.**

  - *n***s**

    **substitute the next** *n* **characters (i.e., delete the characters** **and go into insert mode).**

  - **S**

    **substitute whole line: all characters from the first non-blank character** **to the end of line are deleted and insert mode is entered.**

  - *n***c***move-cmd*

    **change from the current position to the position resulting from** *n* *move-cmd***s (i.e., delete the indicated region and go into insert mode);** **if** *move-cmd* **is c, the line starting from the first non-blank** **character is changed.**

  - **C**

    **change from the current position to the end of the line (i.e., delete to** **the end of the line and go into insert mode).**

  - *n***x**

    **delete the next** *n* **characters.**

  - *n***X**

    **delete the previous** *n* **characters.**

  - **D**

    **delete to the end of the line.**

  - *n***d***move-cmd*

    **delete from the current position to the position resulting from** *n* *move-cmd***s;** *move-cmd* **is a movement command (see above) or d, in which case** **the current line is deleted.**

  - *n***r***c*

    **replace the next** *n* **characters with the character** *c***.**

  - *n***R**

    **replace: enter insert mode but overwrite existing characters instead of** **inserting before existing characters.  The replacement is repeated** *n* **times.**

  - *n***~**

    **change the case of the next** *n* **characters.**

  - *n***y***move-cmd*

    **yank from the current position to the position resulting from** *n* *move-cmd***s into the yank buffer; if** *move-cmd* **is y, the** **whole line is yanked.**

  - **Y**

    **yank from the current position to the end of the line.**

  - *n***p**

    **paste the contents of the yank buffer just after the current position,** *n* **times.**

  - *n***P**

    **same as p, except the buffer is pasted at the current position.**

- Miscellaneous vi commands

  - **^J** and **^M**

    **the current line is read, parsed and executed by the shell.**

  - **^L** and **^R**

    **redraw the current line.**

  - *n***.**

    **redo the last edit command** *n* **times.**

  - **u**

    **undo the last edit command.**

  - *intr* and *quit*

    **the interrupt and quit terminal characters cause the current line to** **be deleted and a new prompt to be printed.**

- Missing vi commands

  **The following vi commands are in the original Korn shell, but are not** **yet in pdksh:**

  - **U**

    **undo all changes that have been made to the current line.**

## FILES

**~/.profile**\
 **/etc/profile**\
 **/etc/suid\_profile**

## BUGS

**Any bugs in pdksh should be reported to pdksh@cs.mun.ca.  Please** **include the version of pdksh (echo $KSH\_VERSION shows it), the machine,** **operating system and compiler you are using and a description of how to** **repeat the bug (a small shell script that demonstrates the bug is** **best).  The following, if relevant (if you are not sure, include them),** **can also helpful: options you are using (both options.h options and set** **-o options) and a copy of your config.h (the file generated by the** **configure script).  New versions of pdksh can be obtained from** **ftp.cs.mun.ca:pub/pdksh/.**

## AUTHORS

**This shell is based on the public domain 7th edition Bourne shell clone by** **Charles Forsyth and parts of the BRL shell by Doug A. Gwyn, Doug Kingston,** **Ron Natalie, Arnold Robbins, Lou Salkind and others.  The first release** **was created by Eric Gisin, and it was subsequently maintained by** **John R. MacMillan (chance!john@sq.sq.com), and** **Simon J. Gerraty (sjg@zen.void.oz.au).  The current maintainer is** **Michael Rendell (michael@cs.mun.ca).** **The CONTRIBUTORS file in the source distribution contains a more complete** **list of people and their part in the shell's development.**

## SEE ALSO

**[awk(1)](/awk/1.md),**  **[sh(1)](/sh/1.md),** **[csh(1)](/csh/1.md), [ed(1)](/ed/1.md), [getconf(1)](/getconf/1.md), [getopt(1)](/getopt/1.md), [sed(1)](/sed/1.md), [stty(1)](/stty/1.md), [vi(1)](/vi/1.md),** **[dup(2)](/dup/2.md), [execve(2)](/execve/2.md), [getgid(2)](/getgid/2.md), [getuid(2)](/getuid/2.md), [open(2)](/open/2.md), [pipe(2)](/pipe/2.md), [wait(2)](/wait/2.md),** **[getopt(3)](/getopt/3.md), [rand(3)](/rand/3.md), [signal(3)](/signal/3.md), [system(3)](/system/3.md),** **[environ(5)](/environ/5.md)**

*The KornShell Command and Programming Language*, **Morris Bolsky and David Korn, 1989, ISBN 0-13-516972-0.**

*UNIX Shell Programming*, **Stephen G. Kochan, Patrick H. Wood, Hayden.**

*IEEE Standard for information Technology - Portable Operating System Interface (POSIX) - Part 2: Shell and Utilities*, **IEEE Inc, 1993, ISBN 1-55937-255-9.**