Regular expression also called RegEx, is a pattern of characters used to find, replace, split text from a given string and also validates input. Regular expression is case sensitive. It allows to works with single character to a complicated string pattern easily.
PHP Regular expression functions
preg_match()
finds only first match of searched string in given string. If found returns true.
preg_match_all()
finds all matches in a given string.
preg_replace()
It finds the searched pattern string and replace it with given string and returns new string.
preg_split()
It searches the given pattern in a string and split the string and returns array.
preg_quote()
It adds backslash at the beginning and where the match found in a given string.
Regular Expression Modifiers
i
case sensitive search and replace
m
multiline search and replace (By default single line)
u
Matches UTF-8 characters
Regular Expression Patterns
[abc]
[Hello]
Find string or characters inside brackets
[^abc]
[^Hello Worldz]
Do not find string or characters inside brackets
[a-z]
[l-o] [^Hello Worldz]
Finds all character From l to O in a given string and replace it.
[A-z]
[l-o] [^Hello Worldz]
Finds all Uppercase and lowercase character From l to O in a given string and replace it.
[A-Z]
[H-W] [^Hello Worldz]
Finds all Uppercase character From H to W in a given string and replace it.
[123]
Finds digit(s) in given string
[0-5]
Find digit from 0 to 5 in given string.
[Hello|Hi]
Either of text
Metacharacters
|
any of given characters or string
.
any single character
^
start of the string
$
find match at the end of string
()
to group expression
[]
given characters inside bracket
[^]
not any given characters inside bracket
\d
find digits from 0-9
\D
do not find digits
\w
finds any digit or character
\W
do not any digit or character
\b
Find match at the beginning of sentence
\s
Finds whitespace character, newline or tab
\S
Finds non-whitespace character, newline or tab
\uxxxx
Quantifiers
r+
Matches any string if contain at least one r
r*
Matches any string if contain one or more r
r?
Matches any string if contain one or zero r
r{a}
matches any string with a sequence of A r’s.
r{a,b}
Matches any string which contains sequence of A to B r’s
r{a,}
Matches any string which contains sequence of at least A r’s