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replace

Note

This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information.

Returns $haystack with any substring matching $pattern replaced by $replacement

namespace HH\Lib\Regex;

function replace(
  string $haystack,
  Pattern<Match> $pattern,
  string $replacement,
  int $offset = 0,
): string;

If $offset is given, replacements are made only starting from $offset. The regex pattern follows the PCRE library: https://www.pcre.org/original/doc/html/pcresyntax.html.

Throws InvariantException if $offset is not within plus/minus the length of $haystack.

Guide​

Parameters​

  • string $haystack
  • Pattern<Match> $pattern
  • string $replacement
  • int $offset = 0

Returns​

  • string