Replace

:::info[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 the "haystack" string with all occurrences of $needle replaced by $replacement

namespace HH\Lib\Str;

function replace(
  string $haystack,
  string $needle,
  string $replacement,
): string;

• For a case-insensitive search/replace, see Str\replace_ci().
• For multiple case-sensitive searches/replacements, see Str\replace_every().
• For multiple case-insensitive searches/replacements, see Str\replace_every_ci().

Guide

• String

Parameters

• string $haystack
• string $needle
• string $replacement

Returns

• string

Examples

$result = Str\replace("example_string", "string", "replacement");
echo($result);
//result: "example_replacement"

$result = Str\replace("example_string", "STRING", "replacement");
echo($result);
//result: "example_string"

$result = Str\replace("example_string", "uncontained", "replacement");
echo($result);
//result: "example_string"