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PHP preg_replace Examples

This post gives some simple examples for using regular expressions with preg_replace() in PHP scripts.

Syntax

While full syntax is

mixed preg_replace ( mixed $pattern , mixed 
    $replacement , mixed $subject [, int $limit = -1 [, int &$count ]] )

you might to use the simpler examples given below:

Simple Replacing

$result = preg_replace('/abc/', 'def', $string);   # Replace all 'abc' with 'def'
$result = preg_replace('/abc/i', 'def', $string);  # Replace with case insensitive matching
$result = preg_replace('/\s+/', '', $string);      # Strip all whitespaces

Advanced Usage

Multiple replacements

$result = preg_replace(
    array('/pattern1/', '/pattern2/'),
    array('replace1', 'replace2'),
    $string
);

Replacing with Back References

Back references allow you to re-insert a match captured using braces. There are different ways to write a back reference e.g. \\1, $1, ${1} for the first back reference:

$result = preg_replace('/abc(def)hij/', '/\\1/', $string);
$result = preg_replace('/abc(def)hij/', '/$1/', $string);
$result = preg_replace('/abc(def)hij/', '/${1}/', $string);

Perform only a limited number of replacements

# Perform maximum of 5 replacements
$result = preg_replace('/abc/', 'def', $string, -1, 5);

Multi-line replace

# Strip HTML tag
$result = preg_replace('<span id="15">.*</span>#m', '', $string);