--- name: "readlinebuf" section: "3bobcat" platform: "linux" package: "libbobcat-dev" version: "6.07.01-2" release: "Debian 13 (Trixie)" platforms: ["linux"] url: "https://new.carta.tech/readlinebuf" --- # readlinebuf(3bobcat) std::streambuf offering line-editing and history ## NAME FBB::ReadLineBuf - std::streambuf offering line-editing and history ## SYNOPSIS **#include \**\ Linking option: -lbobcat -lreadline ## DESCRIPTION The **FBB::ReadLineBuf** object may be used as a *std::streambuf* of *std::istream* objects, allowing line-editing and history manipulation. The **ReadLineBuf** class uses Gnu’s readline library to allow editing of input lines. The *ReadLineBuf* object can be used to construct a *std::istream* allowing in-line editing of lines read from the terminal. All lines may be preceded by a configurable prompt. Since Gnu’s readline library operates on global data there can only be one **ReadLineBuf** object. Therefore **ReadLineBuf** is a singleton class: in any program there can only be one **ReadLineBuf** object (Gnu’s readline library does, however, offer functions allowing programs to use multiple histories. So it would in principle be possible to design a non-singleton *ReadLineBuf* class. Since programs normally only interact with a single terminal, there is probably little use for non-singleton **ReadLineBuf** class). **ReadLineBuf** offers editing capabilities while the user is entering lines. Like Gnu’s [**readline**(3)](/readline/3.md) function, the line editing commands are by default similar to those of [**emacs**(1)](/emacs/1.md), but can easily be reconfigured, e.g. to offer [**vi**(1)](/vi/1.md)-like characteristics. History manipulation is provided as an option. The collected history may be accessed for reading using an **FBB::ReadLineHistory** object. Specific information about the facilities offered by the Gnu software used by **ReadLineBuf** is provided in the GNU Readline Library documentation (*http://cnswww.cns.cwru.edu/php/chet/readline/rltop.html*). Gnu’s *readline* function reads its information from the standard input file. Programs using *ReadLineBuf* should normally not extract information from *std::cin*. However, as the standard input file has a file descriptor (0), redirection should be possible (e.g., using *FBB::Redirector*). When the command line is kept, history expansion is offered as an option. History expansion introduces words from the history list into the input stream, making it easy to repeat commands, to insert elements of a previous input line into the current input line, or to fix errors in previous command lines. History expansion is usually performed immediately after a complete line is read. The line selected from the history is called the *event*, and the portions of that line that are processed are called *words*. Various modifiers are available to manipulate selected words. This is comparable to the way a program like [**bash**(1)](/bash/1.md) breaks up its input line into \`words’. History expansion is introduced by the use of the history expansion character, by default equal to the *!*-character. Only backslash (*\\*) and single quotes can change the history expansion character into a normal character. The remainder of this section is copied almost verbatim from the [**history**(3)](/history/3.md) man-page. The reader is referred to that man-page or to the Gnu History Library documentation for further details. The following **event designators** are supported: - o *!*: starts a history substitution, except when followed by a blank, newline, *=* or *(*. - o *!n*: refers to command line n. - o *!-n*: refers to the current command line minus n. - o *!!* refers to the previous command. This is a synonym for \`!-1’. - o *!string* refers to the most recent command starting with string. - o *!?string\[?\]* refers to the most recent command containing string. The trailing *?* may be omitted if string is followed immediately by a newline. - o *^string1^string2^* (quick substitution) repeats the last command, replacing *string1* with *string2*. Equivalent to *!!:s/string1/string2/*. - o *!#* the entire command line typed so far. **Word Designators** Word designators are used to select desired words from the event. A *:* separates the event specification from the word designator. It may be omitted if the word designator begins with a *^, $, \*, -*, or *%*. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces. - o *0* (zero) The zeroth word. For the shell, this is the command word. - o *n* The nth word. - o *^* The first argument. That is, word 1. - o *$* The last argument. - o *%* The word matched by the most recent *?string?* search. - o *x-y* A range of words; \`-y’ abbreviates \`0-y’. - o *\** All of the words but the zeroth. This is a synonym for *1-$*. It is not an error to use \* if there is just one word in the event; the empty string is returned in that case. - o *x\** Abbreviates *x-$*. - o *x-* Abbreviates *x-$* like *x\**, but omits the last word. If a word designator is supplied without an event specification, the previous command is used as the event. **Modifiers** After the optional word designator, there may appear a sequence of one or more of the following modifiers, each preceded by a *:*. - o *h* removes a trailing file name component, leaving only the head. - o *t* removes all leading file name components, leaving the tail. - o *r* removes a trailing suffix of the form *.xxx*, leaving the basename. - o *e* removes all but the trailing suffix. - o *p* prints the new command but does not execute it. - o *q* quotes the substituted words, escaping further substitutions. - o *x* quotes the substituted words as with q, but break into words at blanks and newlines. - o *s/old/new/* substitutes new for the first occurrence of old in the event line. Any delimiter can be used in place of */*. The final delimiter is optional if it is the last character of the event line. The delimiter may be quoted in old and new with a single backslash. If *&* appears in new, it is replaced by old. A single backslash will quote the *&*. If *old* is null, it is set to the last old substituted, or, if no previous history substitutions took place, the last string in a *!?string\[?\]* search. - o *&* repeats the previous substitution. - o *g* Causes changes to be applied over the entire event line. This is used in conjunction with *:s* (e.g., *:gs/old/new/*) or *:&*. If used with *:s*, any delimiter can be used in place of */*, and the final delimiter is optional if it is the last character of the event line. An a may be used as a synonym for *g*. - o *G* Apply the following *s* modifier once to each word in the event line. ## NAMESPACE **FBB**\ All constructors, members, operators and manipulators, mentioned in this man-page, are defined in the namespace **FBB**. ## INHERITS FROM *std::streambuf* ## ENUMERATIONS The *enum Type* defines the following value: - o *DONT\_EXPAND\_HISTORY*: history expansion is not requested; - o *EXPAND\_HISTORY*: history expansion is requested. The *enum Expansion* provides meaningful return values for the history expansion process. Its values are: - o *DONT\_EXEC*: history expansion succeeded, but the expanded line should not be executed. E.g., after entering the line ``` ls * ``` the line ``` !!:p ``` should cause the using program to *display*, rather than exectute *ls* *\**. Note that interpretation of this expansion return value is not the task of the **ReadLineBuf** object, but of the program using the **ReadLineBuf** object. - o *ERROR*: the history expansion failed. See also the member *expansionError* below; - o *EXPANDED*: the history expansion succeeded; - o *NO\_EXPANSION*: no history expansion took place. ## STATIC MEMBERS - o **ReadLineBuf &initialize(std::string const &prompt = "", Type type =** **NO\_EXPANSION)**:\ This static member returns the *ReadLineBuf* using an initial prompt, using a history of at most *std::numeric\_limits\::max()* lines, and by default not using history expansion. If the object has already been initialized a *logic\_error* exception is thrown. - o **ReadLineBuf &initialize(std::string const &prompt, size\_t historySize,** **Type type = NO\_EXPANSION)**:\ This static member initializes the *ReadLineBuf* using an initial prompt, an initial history of a predefined maximum size, and by default not using history expansion. Specifying a history size 0 results in no history being kept, any value equal to or exceeding the predefined constant *std::numeric\_limits\::max()* results in a history of at most *std::numeric\_limits\::max()* lines. If no history is requested but *type* is specified as *EXPAND\_HISTORY* a *logic\_error* exception is thrown. A *logic\_error* is also thrown if the object has already been initialized. - o **ReadLineBuf &instance()**:\ This static member returns the already initialized *ReadLineBuf* object. If the object has not yet been initialized a *logic\_error* exception is thrown. ## CONSTRUCTORS As the class **ReadLineBuf** is a singleton class it offers no public constructors, nor are overloaded assignment operators available. ## MEMBER FUNCTIONS All members of **std::streambuf** are available, as **FBB::ReadLineBuf** inherits from this class. - o **ReadLineBuf::Expansion expansion() const**:\ The status of the history expansion after retrieving a line from the terminal is returned. Its value is determined after each line retrieved from the terminal. If no history expansion is requested it returns *Expansion::ERROR*. - o **std::string const &expansionError() const**:\ A short textual description of the nature of the error when *expansion* returns *Expansion::ERROR* is returned. If no history expansion is requested an empty string is returned. - o **bool setExpansion(Type type)**:\ History expansion can be activated or stopped using this member. When history expansion is requested but the **ReadLineBuf** object maintains no history the function returns *false*. Otherwise it returns *true*. - o **void setPrompt(std::string const &prompt = "")**:\ The prompt that is displayed in front of the next line read from the terminal can be modified by this member. When called without arguments no prompt will be displayed. *setPrompt* can be called while input lines are being received. The new prompt will be active after the current line has been read from the terminal. - o **bool useTimestamps(std::string (\*timestamp)() = 0)**:\ When initialized with the address of a function returning a *std::string* the entered commands will be given a timestamp equal to the text returned by the function pointed to by *timestamp*. The timestamps can be retrieved using the **ReadLineHistory**(3) object. By default or after passing an explicit 0-pointer to *useTimestamps* no timestamps are stored. The value *false* is returned when no history is kept, otherwise *true* is returned. ## EXAMPLE ``` #include #include #include #include #include #include using namespace std; using namespace FBB; int main() { ReadLineBuf &readlineBuf = ReadLineBuf::initialize("", 10, ReadLineBuf::EXPAND_HISTORY); istream in(&readlineBuf); size_t count = 0; string line; while (true) { ostringstream prompt; prompt << setw(2) << ++count << ": "; readlineBuf.setPrompt(prompt.str()); if (!getline(in, line)) // uses the last-set prompt break; cout << "Retrieved: " << line << "\n" "Expansion status: "; switch (readlineBuf.expansion()) { case ReadLineBuf::ERROR: cout << "ERROR: " << readlineBuf.expansionError() << ’\n’; break; case ReadLineBuf::NO_EXPANSION: cout << "no expansion performed\n"; break; case ReadLineBuf::DONT_EXEC: cout << "don’t execute the expanded line\n"; break; case ReadLineBuf::EXPANDED: cout << "expansion successfully performed\n"; break; } } } ``` ## FILES *bobcat/readlinebuf* - defines the class interface ## SEE ALSO [**bobcat**(7)](/bobcat/7.md), [**readline**(3)](/readline/3.md), [**readlinehistory**(3bobcat)](/readlinehistory/3bobcat.md), [**readlinestream**(3bobcat)](/readlinestream/3bobcat.md) ## BUGS None Reported. ## BOBCAT PROJECT FILES - o *https://fbb-git.gitlab.io/bobcat/*: gitlab project page; Debian Bobcat project files: - o *libbobcat6*: debian package containing the shared library, changelog and copyright note; - o *libbobcat-dev*: debian package containing the static library, headers, manual pages, and developer info; ## BOBCAT Bobcat is an acronym of \`Brokken’s Own Base Classes And Templates’. ## COPYRIGHT This is free software, distributed under the terms of the GNU General Public License (GPL). ## AUTHOR Frank B. Brokken (**f.b.brokken@rug.nl**).