Understanding PHP preg_replace: Syntax, Parameters, and Practical Examples
This article explains PHP's preg_replace function, detailing its signature, parameter meanings, return values, and providing multiple code examples that demonstrate pattern matching, backreferences, array handling, and replacement limits for effective string manipulation in backend development.
preg_replace() executes a regular expression search and replace in PHP.
It searches the $subject for matches to $pattern and replaces them with $replacement . Optional parameters $limit and &$count control the maximum replacements and capture the number of replacements performed.
Parameters
pattern : the regex pattern or an array of patterns; PCRE modifiers (including the deprecated e ) may be used.
replacement : the replacement string or array; can contain back‑references such as \$1 or \\1 , with special handling for adjacent digits (e.g., ${1}1 ).
subject : the string or array to be processed; if an array, the function returns an array of results.
limit : maximum number of replacements per pattern (default -1 for unlimited).
count : variable passed by reference that receives the total number of replacements.
Return value : the modified string, or an array when subject is an array; NULL is returned on error.
Example 1
Output: April1,2003
Example 2
Output: The bear black slow jumped over the lazy dog.
Example 3
Output: $startDate=5/27/1999
Example 4
Output: foo o
Example 5
Output: *** to and the replacement count 3 .
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