php - What are colons for in a preg_match pattern? -

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in following php code (not mine):

$has_trailing_slash = preg_match(':/$:', $string);

what purpose of colons? if remove them, preg_match call complains if there isn't trailing slash in string. colons, preg_match doesn't complain if there isn't trailing slash. apparently colons kind of conditional or optional indicator, documented anywhere? can't find 1 word of documentation using colons way preg_match, or regex in general.

the colons here used delimiters.

you need use delimiters regex in php regex engine can know regex starts , regex ends, , excluding quotes use in function.

this particularly important regex engine can distinguish between actual regular expression , flags (if any) used (e.g. i (for case insensitive matching), s (to make dot match newlines), u (to allow unicode character matching), etc)

you can use variety of delimiters , can use 'suitable' 1 depending on situation. instance, common delimiter use forward slash: /. when use forward slash delimiter, have escape forward slashes in regular expression (by using backslash).

otherwise, can change delimiter , said, can use a delimiter such #, or ! or | or ~ or {} , on, long it's not alphanumeric or backslash.

this means can use:

preg_match(':/$:', $string); preg_match('"/$"', $string); preg_match('@/$@', $string); preg_match('{/$}', $string);

but if use /, you'll have escape / in regex so:

preg_match('/\/$/', $string);   # either use backslash preg_match('/[/]$/', $string);  # or wrap around square brackets

or weird this:

preg_match('\'/$\'', $string);

using confuse people reading code , regex can considered confusing enough!

conclusion, have wide variety of delimiters choose from, it's preferable if consistent , try not make code confusing.


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