When using the PCRE functions, it is required that the pattern is enclosed by delimiters. A delimiter can be any non-alphanumeric, non-backslash, non-whitespace character.

Often used delimiters are forward slashes (/), hash signs (#) and tildes (~). The following are all examples of valid delimited patterns.

/foo bar/

It is also possible to use bracket style delimiters where the opening and closing brackets are the starting and ending delimiter, respectively. (), {}, [] and <> are all valid bracket style delimiter pairs.

(this [is] a (pattern))
{this [is] a (pattern)}
[this [is] a (pattern)]
<this [is] a (pattern)>
Bracket style delimiters do not need to be escaped when they are used as meta characters within the pattern, but as with other delimiters they must be escaped when they are used as literal characters.

If the delimiter needs to be matched inside the pattern it must be escaped using a backslash. If the delimiter appears often inside the pattern, it is a good idea to choose another delimiter in order to increase readability.

The preg_quote() function may be used to escape a string for injection into a pattern and its optional second parameter may be used to specify the delimiter to be escaped.

You may add pattern modifiers after the ending delimiter. The following is an example of case-insensitive matching:


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User Contributed Notes 5 notes

Pedro Gimeno
2 years ago
Note that bracket style opening and closing delimiters aren't a 100% problem-free solution, as they need to be escaped when they aren't in matching pairs within the expression. That mismatch can happen when they appear inside character classes [...], as most meta-characters lose their special meaning. Consider these examples:

('{[{]}', ''); // Warning: preg_match(): No ending matching delimiter '}'
preg_match('{[}]}', ''); // Warning: preg_match(): Unknown modifier ']'
preg_match('{[}{]}', ''); // Warning: preg_match(): Unknown modifier ']'

Escaping them solves it:

('{[\{]}', ''); // OK
preg_match('{[}]}', ''); // OK
preg_match('{[\}\{]}', ''); // OK
1 year ago
The dirty little delimiter secret they don't tell you ->
Examples: Balanced delims {\d{2}Some\\{33\\}\w{5}} parses to
\d{2}Some\\{33\\}\w{5} and {\d{2}Some\{33\}\w{5}} parses to \d{2}Some{33}\w{5}. 
Un-Balanced delims +\d{2}Some\+33\+\w{5}+ parses to \d{2}Some+33+\w{5} and
+\d{2}Some\\+33\\+\w{5}+ won't parse because the delimiter is unescaped.
2 years ago
preg_match('{[}]}', ''); // Warning: preg_match(): Unknown modifier ']'

preg_match('{[\}]}', ''); // OK
hmelin at ya dot ru
1 year ago
A delimiter can be any ASCII non-alphanumeric, non-backslash, non-whitespace character:  !"#$%&'*+,./:;=?@^_`|~-  and  ({[<>]})
cissyyau77 at yahoo dot com dot hk
3 months ago
you guys can call me for sex
+852 92606871
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