PCRE2_SUBSTITUTE(3)

💅 PCRE2_SUBSTITUTE(3) — Library Functions Manual 💅

okay bestie, this is the PCRE2_SUBSTITUTE(3) page from the Library Functions Manual — the function that matches a compiled regex against a subject and then does the substitution glow-up. ✨

🌸 NAME 🌸

PCRE2 — Perl-compatible regular expressions (revised API) 💖

✨ SYNOPSIS ✨

#include <pcre2.h>

int pcre2_substitute(const pcre2_code *code, PCRE2_SPTR subject,
  PCRE2_SIZE length, PCRE2_SIZE startoffset,
  uint32_t options, pcre2_match_data *match_data,
  pcre2_match_context *mcontext, PCRE2_SPTR replacement,
  PCRE2_SIZE rlength, PCRE2_UCHAR *outputbuffer,
  PCRE2_SIZE *outlengthptr);

🦋 DESCRIPTION 🦋

This function matches a compiled regular expression against a given subject string, using a matching algorithm that is similar to Perl's. Then it makes a copy of the subject and substitutes a replacement string for what was matched. 💅

the arguments, fr fr 🫶

• code — points to the compiled pattern.
• subject — points to the subject string.
• length — length of the subject string.
• startoffset — offset in the subject at which to start matching.
• options — option bits.
• match_data — points to a match data block, or is NULL.
• mcontext — points to a match context, or is NULL.
• replacement — points to the replacement string.
• rlength — length of the replacement string.
• outputbuffer — points to the output buffer.
• outlengthptr — points to the length of the output buffer.

A match data block is needed only if you want to inspect the data from the final match that is returned in that block, or if PCRE2_SUBSTITUTE_MATCHED is set. 🫶

A match context is needed only if you want to:

• Set up a callout function.
• Set a matching offset limit.
• Change the backtracking match limit.
• Change the backtracking depth limit.
• Set custom memory management in the match context.

code units + output length — important!! 📏

The length, startoffset, and rlength values are code units, not characters — same for the contents of the variable pointed at by outlengthptr. That variable must contain the length of the output buffer when the function is called. If the function is successful, the value is changed to the length of the new string, excluding the trailing zero that is automatically added. 💖

The subject and replacement lengths can be given as PCRE2_ZERO_TERMINATED for zero-terminated strings. The options are:

• PCRE2_ANCHORED — match only at the first position.
• PCRE2_ENDANCHORED — match only at end of subject.
• PCRE2_NOTBOL — subject is not the beginning of a line.
• PCRE2_NOTEOL — subject is not the end of a line.
• PCRE2_NOTEMPTY — an empty string is not a valid match.
• PCRE2_NOTEMPTY_ATSTART — an empty string at the start of the subject is not a valid match.
• PCRE2_NO_JIT — do not use JIT matching.
• PCRE2_NO_UTF_CHECK — do not check for UTF validity in the subject or replacement (only relevant if PCRE2_UTF was set at compile time).
• PCRE2_SUBSTITUTE_EXTENDED — do extended replacement processing.
• PCRE2_SUBSTITUTE_GLOBAL — replace all occurrences in the subject.
• PCRE2_SUBSTITUTE_LITERAL — the replacement string is literal.
• PCRE2_SUBSTITUTE_MATCHED — use pre-existing match data for first match.
• PCRE2_SUBSTITUTE_OVERFLOW_LENGTH — if overflow, compute needed length.
• PCRE2_SUBSTITUTE_REPLACEMENT_ONLY — return only replacement string(s).
• PCRE2_SUBSTITUTE_UNKNOWN_UNSET — treat unknown group as unset.
• PCRE2_SUBSTITUTE_UNSET_EMPTY — simple unset insert = empty string.

If PCRE2_SUBSTITUTE_LITERAL is set, PCRE2_SUBSTITUTE_EXTENDED, PCRE2_SUBSTITUTE_UNKNOWN_UNSET, and PCRE2_SUBSTITUTE_UNSET_EMPTY are ignored. 🚨

⚠️ If PCRE2_SUBSTITUTE_MATCHED is set, match_data must be non-NULL; its contents must be the result of a call to pcre2_match() (or pcre2_jit_match()) using the same pattern, subject pointer, effective subject length, start offset, and match options.

The function returns the number of substitutions, which may be zero if there are no matches. The result may be greater than one only when PCRE2_SUBSTITUTE_GLOBAL is set. In the event of an error, a negative error code is returned. 😭

There is a complete description of the PCRE2 native API in the pcre2api page and a description of the POSIX API in the pcre2posix page. 🦋

---

mwah 💋 — PCRE2 10.47, 03 October 2025, PCRE2_SUBSTITUTE(3).