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:
<?php
preg_match('{[{]}', ''); // 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:
<?php
preg_match('{[\{]}', ''); // OK
preg_match('{[}]}', ''); // OK
preg_match('{[\}\{]}', ''); // OK
?>
Delimitatori
Quando si usano le funzioni PCRE, il pattern deve essere racchiuso da delimitatori. Un delimitatore può essere qualsiasi carattere non alfanumerico, esclusi il backslash e i caratteri di spazio (spazio, tab, ecc.).
Delimitatori usati spesso sono la barra "slash" (/), il cancelletto "hash"
(#) e la tilde (~). I
seguenti sono esempi di delimitazioni valide dei pattern:
/foo bar/ #^[^0-9]$# +php+ %[a-zA-Z0-9_-]%
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.
/http:\/\// #http://#
In addition to the aforementioned delimiters, it is also possible to use bracket style delimiters where the opening and closing brackets are the starting and ending delimiter, respectively.
{this is a pattern}
You may add pattern modifiers after the ending delimiter. The following is an example of case-insensitive matching:
#[a-z]#i
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User Contributed Notes 3 notes
Pedro Gimeno ¶
9 years ago
