Regular expression replace : REGEX

Posted under » PHP on 7 July 2011

Metacharacter

.* words in between
^ Beginning of string
$ End of string
. Any character except a newline character
? one match
\s A single whitespace character
\S A single non-whitespace character
\d A digit between 0 and 9
\w An alphabetic or numeric character, or underscore
[A-Z] An uppercase alphabetic character
[a-z] A lowercase alphabetic character
[\r\n]+ or (\r\n|\r|\n) new line
[0-9] A digit between 0 and 9
| OR logical operator
(?= Positive conditional test
(?! Negative conditional test
/, @ and # at the beginning and end of the regex pattern

ba.*bi The string "foo" in "bafoobi"
foo The string "foo"
^foo "foo" at the start of a string
foo$ "foo" at the end of a string
^foo$ "foo" when it is alone on a string
[abc] a, b, or c
[^-\s] or [^\s-] not a whitespace
[a-z] Any lowercase letter
[^A-Z] Any character that is not a uppercase letter
(gif|jpg) Matches either "gif" or "jpeg"
[a-z]+ One or more lowercase letters
[0-9\.\-] Аny number, dot, or minus sign
^[a-zA-Z0-9_]{1,}$ Any word of at least one letter, number or _
([wx])([yz]) wy, wz, xy, or xz
[^A-Za-z0-9] Any symbol (not a number or a letter)
([A-Z]{3}|[0-9]{4}) Matches three letters or four numbers

Matching and groups. eg.

/\\";(.*)content:\\"/gm #regex

\"; }\r\n\r\n. whuteva bp3-i  content:\" #string

g = global and m = multiline. The brackets is to place the wildcard

Simple replace

preg_replace("/([Cc]opyright) 200(3|4|5|6)/", "$1 2011", "Copyright 2009");
// Copyright 2011

One match at a time

preg_replace('/(\$.*?\$)/', '-$1-', 'Differentiate $\sqrt[3]{x}$ with respect to ${x}$.');
// Differentiate -$\sqrt[3]{x}$- with respect to -${x}$-.

Note that at times, you have to use single stroke ' instead of "" or regex replace does not work.

Reordering

preg_replace("/(\d+)-(\d+)-(\d+)/", "$2/$3/$1", "2011-01-27");
// 01/27/2011

Array replace

$search = array ( "/(\w{6}\s\(w{2})\s(\w+)/e",
                  "/(\d{4})-(\d{2})-(\d{2})\s(\d{2}:\d{2}:\d{2})/");
$replace = array ('"$1 ".strtoupper("$2")',
                  "$3/$2/$1 $4");
$word = "Deleted on | 2011-02-15 05:43:41";     
preg_replace($search, $replace, $word);
// Deleted on | 15/02/2011 05:43:41

Remove invisible content

$search = array ('@<head[^>]*?>.*?</head>@siu',
	'@<style[^>]*?>.*?</style>@siu',
	'@<script[^>]*?.*?</script>@siu');
$replace = array (' ', ' ', ' ');
$word = "some html page";

Not everytime you want to replace the text. Sometimes you just want to find and/or separate them.

This regex tool is very useful.