---
name: "re"
section: "3"
platform: "macos"
package: "ksh"
version: "42"
release: "macOS 26.5"
platforms: ["macos"]
url: "https://new.carta.tech/re/3"
---

# re(3)

regular expression library

## NAME

recomp, reexec, ressub, refree, reerror − regular expression library

## SYNOPSIS

```
#include <re.h>
Re_program_t* recomp(char* pattern, int flags);
int reexec(Re_program_t* re, char* source);
void ressub(Re_program_t* re, Sfio_t* sp, char* old, char* new, int flags);
void reerror(char* message);
void refree(Re_program_t* re);
```

## DESCRIPTION

$1$2recomprecomprecomprecomprecomprecomprecomprecomp compiles a regular expression in *pattern* and returns a pointer to the compiled regular expression. The space is allocated by [*malloc*(3)](/malloc/3.md) and may be released by $1$2refreerefreerefreerefreerefreerefreerefreerefree Regular expressions are as in [*egrep*(1)](/egrep/1.md) except that newlines are treated as ordinary characters and $1$2$$$$$$$$ matches the end of a null-terminated string. *flags* may be $1$2RE\_EDSTYLERE\_EDSTYLERE\_EDSTYLERE\_EDSTYLERE\_EDSTYLERE\_EDSTYLERE\_EDSTYLERE\_EDSTYLE which specifies [*ed*(1)](/ed/1.md) style special characters, $1$2\\(\\(\\(\\(\\(\\(\\(\\( $1$2\\)\\)\\)\\)\\)\\)\\)\\) $1$2\\?\\?\\?\\?\\?\\?\\?\\? $1$2\\+\\+\\+\\+\\+\\+\\+\\+ and $1$2\\\|\\\|\\\|\\\|\\\|\\\|\\\|\\\| for the [*egrep*(1)](/egrep/1.md) $1$2(((((((( $1$2)))))))) $1$2???????? $1$2++++++++ and $1$2\|\|\|\|\|\|\|\| respectively.

$1$2reexecreexecreexecreexecreexecreexecreexecreexec matches the null-terminated *source* string against the compiled regular expression *re* from a previous call to $1$2recomprecomprecomprecomprecomprecomprecomprecomp If it matches, $1$2reexecreexecreexecreexecreexecreexecreexecreexec returns a non-zero value. If *flags* is $1$2RE\_MATCHRE\_MATCHRE\_MATCHRE\_MATCHRE\_MATCHRE\_MATCHRE\_MATCHRE\_MATCH then the array *re-\>match* is filled with character pointers to the substrings of *source* that correspond to the parenthesized subexpressions of  *pattern*: *re-\>match\[i\].sp* points to the beginning and *re-\>match\[i\].ep* points just beyond the end of substring *i*. (Subexpression *i* begins at the *i*th matched left parenthesis, counting from 1.) Pointers in *re-\>match\[0\]* pick out the substring that corresponds to the entire regular expression. Unused elements of *re-\>match* are filled with zeros. Matches involving $1$2\*\*\*\*\*\*\*\* $1$2++++++++ and  $1$2???????? are extended as far as possible. A maximum of 9 subexpressions will be matched. The structure of elements of *re-\>match* is:

```
	typedef struct
	{
		char* sp;
		char* ep;
	} rematch;
```

$1$2ressubressubressubressubressubressubressubressub places in the [*sfio*(3)](/sfio/3.md) stream *sp* a substitution instance of *old* to *new* in *source* in the context of the last $1$2reexecreexecreexecreexecreexecreexecreexecreexec performed on *re-\>match*. Each instance of where *n* is a digit, is replaced by the string delimited by and Each instance of  $1$2&&&&&&&& is replaced by the string delimited by *re-\>match\[0\].sp* and *re-\>match\[0\].ep*. If $1$2RE\_ALLRE\_ALLRE\_ALLRE\_ALLRE\_ALLRE\_ALLRE\_ALLRE\_ALL is set in *flags* then all occurrences of *old* are replaced by *new*. If $1$2RE\_LOWERRE\_LOWERRE\_LOWERRE\_LOWERRE\_LOWERRE\_LOWERRE\_LOWERRE\_LOWER $1$2\[\[\[\[\[\[\[\[ is set in *flags* then *old* is converted to lower \[upper\] case.

$1$2reerror,reerror,reerror,reerror,reerror,reerror,reerror,reerror, called whenever an error is detected in $1$2recomp,recomp,recomp,recomp,recomp,recomp,recomp,recomp, $1$2reexec,reexec,reexec,reexec,reexec,reexec,reexec,reexec, or $1$2ressub,ressub,ressub,ressub,ressub,ressub,ressub,ressub, writes the string *msg* on the standard error file and exits. $1$2reerrorreerrorreerrorreerrorreerrorreerrorreerrorreerror may be replaced to perform special error processing.

## DIAGNOSTICS

$1$2recomprecomprecomprecomprecomprecomprecomprecomp returns 0 for an invalid expression or other failure. $1$2reexecreexecreexecreexecreexecreexecreexecreexec returns 1 if *source* is accepted, 0 otherwise.

## SEE ALSO

[ed(1)](/ed/1.md), [grep(1)](/grep/1.md), [expr(1)](/expr/1.md)