Visit Our UNIX and Linux User Community

Linux and UNIX Man Pages

Test Your Knowledge in Computers #728
Difficulty: Medium
Bjarne Stroustrup was awarded the Computer Pioneer Award for pioneering C++.
True or False?
Linux & Unix Commands - Search Man Pages

preg_replace(3) [php man page]

PREG_REPLACE(3) 							 1							   PREG_REPLACE(3)

preg_replace - Perform a regular expression search and replace

mixed preg_replace (mixed $pattern, mixed $replacement, mixed $subject, [int $limit = -1], [int &$count]) DESCRIPTION
Searches $subject for matches to $pattern and replaces them with $replacement. PARAMETERS
o $pattern - The pattern to search for. It can be either a string or an array with strings. Several PCRE modifiers are also available. o $replacement - The string or an array with strings to replace. If this parameter is a string and the $pattern parameter is an array, all pat- terns will be replaced by that string. If both $pattern and $replacement parameters are arrays, each $pattern will be replaced by the $replacement counterpart. If there are fewer elements in the $replacement array than in the $pattern array, any extra $pat- terns will be replaced by an empty string. $replacement may contain references of the form \ n or (since PHP 4.0.4) $ n, with the latter form being the preferred one. Every such reference will be replaced by the text captured by the n'th parenthesized pattern. n can be from 0 to 99, and \0 or $0 refers to the text matched by the whole pattern. Opening parentheses are counted from left to right (starting from 1) to obtain the number of the capturing subpattern. To use backslash in replacement, it must be doubled ( "\\" PHP string). When working with a replacement pattern where a backreference is immediately followed by another number (i.e.: placing a literal number immediately after a matched pattern), you cannot use the familiar \1 notation for your backrefer- ence. \11, for example, would confuse preg_replace(3) since it does not know whether you want the \1 backreference followed by a literal 1, or the \11 backreference followed by nothing. In this case the solution is to use ${1}1. This creates an isolated $1 backreference, leaving the 1 as a literal. When using the deprecated e modifier, this function escapes some characters (namely ', ", and NULL) in the strings that replace the backreferences. This is done to ensure that no syntax errors arise from backref- erence usage with either single or double quotes (e.g. 'strlen('$1')+strlen("$2")'). Make sure you are aware of PHP's string syntax to know exactly how the interpreted string will look. o $subject - The string or an array with strings to search and replace. If $subject is an array, then the search and replace is performed on every entry of $subject, and the return value is an array as well. o $limit - The maximum possible replacements for each pattern in each $subject string. Defaults to -1 (no limit). o $count - If specified, this variable will be filled with the number of replacements done. RETURN VALUES
preg_replace(3) returns an array if the $subject parameter is an array, or a string otherwise. If matches are found, the new $subject will be returned, otherwise $subject will be returned unchanged or NULL if an error occurred. ERRORS
/EXCEPTIONS As of PHP 5.5.0 E_DEPRECATED level error is emitted when passing in the "e" modifier. As of PHP 7.0.0 E_WARNING is emited in this case and "e" modifier has no effect. CHANGELOG
+--------+---------------------------------------------------+ |Version | | | | | | | Description | | | | +--------+---------------------------------------------------+ | 7.0.0 | | | | | | | Support for the /e modifier has been removed. | | | Use preg_replace_callback(3) instead. | | | | | 5.5.0 | | | | | | | The /e modifier is deprecated. Use | | | preg_replace_callback(3) instead. See the | | | PREG_REPLACE_EVAL documentation for additional | | | information about security risks. | | | | | 5.1.0 | | | | | | | Added the $count parameter | | | | +--------+---------------------------------------------------+ EXAMPLES
Example #1 Using backreferences followed by numeric literals <?php $string = 'April 15, 2003'; $pattern = '/(w+) (d+), (d+)/i'; $replacement = '${1}1,$3'; echo preg_replace($pattern, $replacement, $string); ?> The above example will output: April1,2003 Example #2 Using indexed arrays with preg_replace(3) <?php $string = 'The quick brown fox jumped over the lazy dog.'; $patterns = array(); $patterns[0] = '/quick/'; $patterns[1] = '/brown/'; $patterns[2] = '/fox/'; $replacements = array(); $replacements[2] = 'bear'; $replacements[1] = 'black'; $replacements[0] = 'slow'; echo preg_replace($patterns, $replacements, $string); ?> The above example will output: The bear black slow jumped over the lazy dog. By ksorting patterns and replacements, we should get what we wanted. <?php ksort($patterns); ksort($replacements); echo preg_replace($patterns, $replacements, $string); ?> The above example will output: The slow black bear jumped over the lazy dog. Example #3 Replacing several values <?php $patterns = array ('/(19|20)(d{2})-(d{1,2})-(d{1,2})/', '/^s*{(w+)}s*=/'); $replace = array ('3/4/12', '$1 ='); echo preg_replace($patterns, $replace, '{startDate} = 1999-5-27'); ?> The above example will output: $startDate = 5/27/1999 Example #4 Strip whitespace This example strips excess whitespace from a string. <?php $str = 'foo o'; $str = preg_replace('/ss+/', ' ', $str); // This will be 'foo o' now echo $str; ?> Example #5 Using the $count parameter <?php $count = 0; echo preg_replace(array('/d/', '/s/'), '*', 'xp 4 to', -1 , $count); echo $count; //3 ?> The above example will output: xp***to 3 NOTES
Note When using arrays with $pattern and $replacement, the keys are processed in the order they appear in the array. This is not neces- sarily the same as the numerical index order. If you use indexes to identify which $pattern should be replaced by which $replace- ment, you should perform a ksort(3) on each array prior to calling preg_replace(3). SEE ALSO
PCRE Patterns, preg_quote(3), preg_filter(3), preg_match(3), preg_replace_callback(3), preg_split(3), preg_last_error(3). PHP Documentation Group PREG_REPLACE(3)

Featured Tech Videos