regcomp

Compile a regular expression.

Syntax

   #include <regex.h>

   int regcomp (regex_t *reg, const char *regstr, int flags);

Parameters

reg

points to an object where regcomp() stores the compiled regular expression. regex_t is defined in <regex.h>.

regstr

points to the regular expression as a string (the way it might be specified for a command like grep).

flags

gives a variety of flags for the compilation. Flags are given by symbols defined in <regex.h> which can be ORed together. The recognized symbols are:

REG_EXTENDED: uses extended regular expressions (see regexp(3)). The default is to interpret regstr as a basic regular expression.
REG_ICASE: ignores the case of letters in matches. The setting of LC_CTYPE affects which characters are considered to be opposite cases of each other.
REG_NEWLINE: treats the newline character as a regular character, without its special meaning.
REG_NOSUB: indicates that regcomp() should only report success or failure, and not set reg->re_nsub (see the following section). It also affects the behavior of regexec(3)

Return Values

0: Successful compile
Error code: Not successful compile

Description

regcomp() compiles a regular expression for later use. Early implementations of regcomp() generated executable code that determined whether or not strings matched regstr. Under POSIX.2, regcomp() may generate executable code and/or data which speeds pattern-matching. The result of regcomp() is a structure of the regex_t type which is stored in reg. This structure type contains at least the following field:

size_t re_nsub

is usually set to the number of parenthesized subexpressions found in regstr. These subexpressions are delimited with

\(\)

in basic regular expressions and

()

in extended regular expressions. regcomp() does not set re_nsub if REG_NOSUB is turned on in flags.

Errors

If regcomp() successfully compiles regstr it returns zero; otherwise, it returns one of the following symbolic values:

REG_BADBR

CAUSE

The contents of

\{\}

were invalid: not a number, too large a number, more than two numbers, first number larger than second.

ACTION Make sure that the contents of \{\} or {} are valid.

REG_BADPAT CAUSE regstr was an invalid regular expression.

ACTION Specify a valid regular expression

REG_BADRPT CAUSE regstr contained a ?, *, or + that was not preceded by a valid regular expression.

ACTION Make sure that every unquoted /, *, or + in regstr is preceded by a valid regular expression.

REG_EBRACE CAUSE regstr contained a \{\} imbalance.

ACTION Make sure that all { and } characters and all \{ and \} characters appear in matched pairs in regstr.

REG_EBRACK CAUSE regstr contained a [] imbalance.

ACTION Make sure that all [ and ] characters appear in matched pairs in regstr.

REG_ECOLLATE CAUSE regstr contained a reference to an invalid collating element.

ACTION Make sure that all collating elements referenced in regstr are valid in the locale indicated by LC_COLLATE.

REG_ECTYPE CAUSE regstr contained a reference to an invalid character class.

ACTION Make sure that all character classes referenced in regstr are valid in the locale indicated by LC_CTYPE.

REG_EESCAPE CAUSE regstr contained a trailing \.

ACTION Remove the trailing \ or complete the escape sequence.

REG_ENEWLINE CAUSE A newline was found before the end of a pattern, and the REG_ENEWLINE flag was not set.

ACTION Set the REG_ENEWLINE flag, or check the pattern for a missing /.

REG_EPAREN CAUSE regstr contained a () or \(\) imbalance.

ACTION Make sure that all ( and ) characters and all \( and \) characters appear in matched pairs in regstr.

REG_ERANGE CAUSE A range expression contained an invalid endpoint. For example, an equivalence or character class is not valid.

ACTION Specify a valid endpoint.

REG_ESPACE CAUSE There were not enough free system resources for regcomp() to compile regstr

ACTION Free up more resources or specify a less complex regular expression.

REG_ESUBREG CAUSE The number in a \number construct was greater than the number of matching subexpressions.

ACTION Make sure that number is less than or equal to the number of matching subexpressions.

REG_EFATAL CAUSE An internal error occurred.

ACTION Contact your system manager.

regcomp

Technical documentation

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Syntax

Parameters

Return Values

Description

Errors

See Also