regex.h(7POSIX)

💖 regex.h — regular expression matching types 💖

ok so this one is a page from the POSIX Programmer's Manual (the 7POSIX section, bestie, we're in the overview girlies today). Quick heads up before we dive in:

Heads up, bestie: the Linux implementation of this interface may differ from what's written here (so like, go check the corresponding Linux manual page for the actual Linux tea), or the interface might not even be implemented on Linux at all. 🙈 No cap.

---

✨ PROLOG ✨

This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

---

🌸 NAME 🌸

regex.h — regular expression matching types. it's giving "the header that makes regex go" 💅

---

🎀 SYNOPSIS 🎀

#include <regex.h>

---

🦋 DESCRIPTION 🦋

Okay so the <regex.h> header shall define the structures and symbolic constants used by the regcomp(), regexec(), regerror(), and regfree() functions. it's literally the blueprint, the moment, the blueprint of the moment. ✨

The <regex.h> header shall define the regex_t structure type, which shall include at least the following member:

• size_t re_nsub — Number of parenthesized subexpressions. 👑

The <regex.h> header shall define the size_t type as described in <sys/types.h>.

The <regex.h> header shall define the regoff_t type as a signed integer type that can hold the largest value that can be stored in either a ptrdiff_t type or a ssize_t type.

The <regex.h> header shall define the regmatch_t structure type, which shall include at least the following members:

• regoff_t rm_so — Byte offset from start of string to start of substring.
• regoff_t rm_eo — Byte offset from start of string of the first character after the end of substring.

---

🌈 the cflags constants 🌈

The <regex.h> header shall define the following symbolic constants for the cflags parameter to the regcomp() function:

• REG_EXTENDED — Use Extended Regular Expressions. (the glow-up version ✨)
• REG_ICASE — Ignore case in match. (case? never heard of her 💅)
• REG_NOSUB — Report only success or fail in regexec().
• REG_NEWLINE — Change the handling of <newline>.

---

⭐ the eflags constants ⭐

The <regex.h> header shall define the following symbolic constants for the eflags parameter to the regexec() function:

• REG_NOTBOL — The <circumflex> character ('^'), when taken as a special character, does not match the beginning of string.
• REG_NOTEOL — The <dollar-sign> ('$'), when taken as a special character, does not match the end of string.

---

💜 error return values 💜

The <regex.h> header shall define the following symbolic constants as error return values. bestie these are the "something went wrong" girlies, memorize them fr fr:

• REG_NOMATCH — regexec() failed to match.
• REG_BADPAT — Invalid regular expression.
• REG_ECOLLATE — Invalid collating element referenced.
• REG_ECTYPE — Invalid character class type referenced.
• REG_EESCAPE — Trailing <backslash> character in pattern.
• REG_ESUBREG — Number in \digit invalid or in error.
• REG_EBRACK — "[]" imbalance.
• REG_EPAREN — "\(\)" or "()" imbalance.
• REG_EBRACE — "\{}" imbalance.
• REG_BADBR — Content of "\{}" invalid: not a number, number too large, more than two numbers, first larger than second.
• REG_ERANGE — Invalid endpoint in range expression.
• REG_ESPACE — Out of memory. 😭
• REG_BADRPT — '?', '*', or '+' not preceded by valid regular expression.

---

🧚 the functions 🧚

The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided. yes, we're getting the whole roster 🫶

int    regcomp(regex_t *restrict, const char *restrict, int);
size_t regerror(int, const regex_t *restrict, char *restrict, size_t);
int    regexec(const regex_t *restrict, const char *restrict, size_t,
           regmatch_t [restrict], int);
void   regfree(regex_t *);

The implementation may define additional macros or constants using names beginning with REG_. so like, if you see a REG_ something you don't recognize, that's not you being confused, that's allowed behavior. iykyk 💅

The following sections are informative. (translation: they're the bonus content, not the requirements ✨)

---

🍓 APPLICATION USAGE 🍓

None. (yeah. nothing. empty. a void. but make it official 💀)

---

🌸 RATIONALE 🌸

None. (again! nothing! iconic behavior honestly)

---

🦋 FUTURE DIRECTIONS 🦋

None. (three for three bestie, we love a consistent queen)

---

💖 SEE ALSO 💖

• <sys_types.h>
• The System Interfaces volume of POSIX.1‐2017, regcomp()

---

👑 COPYRIGHT 👑

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

---

okay and that's the whole page bestie, ty for reading 💅 this absolute banger came to you courtesy of IEEE / The Open Group, 2017 — stay matching, stay iconic, and remember: if your regex is unbalanced, that's not a personality trait, that's REG_EPAREN. 🎀✨