Regular Expression examples in php with explanation

Is it only me? I am always scrambling to write regular expressions in one go and always have to look up on what all those symbols do. I am always looking for these stuffs online. Here you will find commonly used regular expression examples. Hope this list will help you all.

Regular Expression

Regular expression is used to describe a pattern of characters. It can match a part of string and can be used for advanced character matching and replacing. We can use preg_match function in PHP for comparing string with regular expression.

Meta characters

Meta characters are used to match specific type of character. Some examples of meta characters are listed below

\d	any digit from 0 to 9
\w	any character from a to z, A to Z and 0 to 9
\s	any white space character (space, tab etc.)
^	starts with
$	ends with
*	means zero or more
+	means one or more
.	match any single character be it letter, number, whitespace etc
\	match meta character by escaping them
i	patterns are case sensitive. Adding i modifier after regular expression makes it case insensitive
[]	square bracket are used to denote character sets. It matches one of any of the characters in the bracket
[ – ]	hyphen specifies a range of characters eg: [0-9] … This matches a single digit between 0 and 9

Some examples of regular expressions

Regular Expression	String	Matches?	Remarks
/abc/	abc	Yes	matches literal abc
/abc/	abczxv	Yes	String still contains abc
/abc/	bcwz	No	Looking for literal abc which is not present in string
/10:20/	10:20:25	Yes
/ab\d/	ab12	Yes	\d matches number
/abc\d/	ab12	No	There is no c
/\d\d/	ab12	Yes
/\w\s\d/	ab 12	Yes
/^abc/	abc	Yes
/^abcxyz/	abcxyz	Yes
/^abc/	123abc	No	Doesn’t start with abc
/abc$/	123abc	Yes
/^abc$/	abc	Yes
/^abc$/	abcxyz	No
/a*bc/	abc	Yes	look for a repeated zero or more times
/a*bc/	bc	Yes
/a+bc/	bc	No	pattern is looking for at least one a
/a+bc/	aaaabc	Yes
/ab.de/	abcde	Yes
/ab.de/	ab4de	Yes
/ab.de/	ab de	Yes
/ab.de/	abde	No
/abc.*/	abcdef	Yes	.* any number of any character
/abc.*/	abc	Yes
/abc\./	abc.	Yes	matches literal dot character
/abc/	Abc	No	pattern are case sensitive
/abc/i	Abc	Yes	i modifier makes pattern case insensitive
/a[123]b/	a2b	Yes
/a[123]b/	a3b	Yes
/a[123]b/	a4b	No
/a[123]+b/	a123233b	Yes
/a[1-5]b/	a2b	Yes	Matches character between 1 and 5
/a[1-5]b/	a8b	No
/[a-z0-9 ]+/	hello world	Yes
/a[^123]b/	a2b	No	^ matches any one character except for the characters specified including ranges
/a[^123]b/	a4b	Yes
/[^a-z]+/	hello	No
/[^a-z]+/	HELLO	Yes