what is the difference between PHP regex and javascript regex

Question

i am working in regex my regex is /\[([^]\s]+).([^]]+)\]/g this works great in PHP for [http://sdgdssd.com fghdfhdhhd] but when i use this regex for javascript it do not match with this input string

my input is [http://sdgdssd.com fghdfhdhhd]

You sure your statement is correct? I'd imagine /\[([^]\s]+).([^]]+)\]/g might work in JS but not PHP; PHP has different modifiers than JS. g is not a PHP modifier. — chris85
– chris85, Commented Dec 7, 2015 at 13:37
this works on PHP you can check it by execute on regex101.com — Junaid
– Junaid, Commented Dec 7, 2015 at 13:57
regex101 isn't a PHP interpretor. That is just a regex tester. eval.in/481587 See php.net/manual/en/reference.pcre.pattern.modifiers.php The regex is valid but it won't work in PHP with that modifier. The PHP functions are global already or there is a function for it to be global (preg_match_all vs. preg_match).. — chris85
– chris85, Commented Dec 7, 2015 at 14:00

Wiktor Stribiżew · Accepted Answer · 2020-02-18 08:36:35Z

13

In JavaScript regex, you must always escape the ] inside a character class:

\[([^\]\s]+).([^\]]+)\]

See the regex demo

JS parsed [^] as *any character including a newline in your regex, and the final character class ] symbol as a literal ].

In this regard, JS regex engine deviates from the POSIX standard where smart placement is used to match [ and ] symbols with bracketed expressions like [^][].

The ] character is treated as a literal character if it is the first character after ^: [^]abc].

In JS and Ruby, that is not working like that:

You can include an unescaped closing bracket by placing it right after the opening bracket, or right after the negating caret. []x] matches a closing bracket or an x. [^]x] matches any character that is not a closing bracket or an x. This does not work in JavaScript, which treats [] as an empty character class that always fails to match, and [^] as a negated empty character class that matches any single character. Ruby treats empty character classes as an error. So both JavaScript and Ruby require closing brackets to be escaped with a backslash to include them as literals in a character class.

Related:

(?1) regex subroutine used to shorten a PCRE pattern conversion - REGEX from PHP to JS

edited Feb 18, 2020 at 8:36

answered Dec 7, 2015 at 13:30

Wiktor Stribiżew

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3 Comments

chris85 Over a year ago

That's strange the the ] doesn't need to be escaped in PCRE. I've always escaped just out of instinct because I thought it would choke on that if not.

Wiktor Stribiżew Over a year ago

@chris85: I just edited the answer since I double checked and found [ does not need to be escaped inside a character class in JS.

Wiktor Stribiżew Over a year ago

Added some more explanations related to this issue.

fictimaph · Accepted Answer · 2017-04-27 17:38:50Z

I would like to add this little fact about translating PHP preg_replace Regex in JavaScript .replace Regex :

<?php preg_replace("/([^0-9\,\.\-])/i";"";"-1 220 025.47 $"); ?>
Result : "-1220025.47"

with PHP, you have to use the quotes "..." around the Regex, a point comma to separate the Regex with the replacement and the brackets are used as a repetition research (witch do not mean the same thing at all.

<script>"-1 220 025.47 $".replace(/[^0-9\,\.\-]/ig,"") </script>
Result : "-1220025.47"

With JavaScript, no quotes around the Regex, a comma to separate Regex with the replacement and you have to use /g option in order to say multiple research in addition of the /i option (that's why /ig).

I hope this will be usefull to someone ! Note that the "\," may be suppressed in case of "1,000.00 $" (English ?) kind of number :

<script>"-1,220,025.47 $".replace(/[^0-9\.\-]/ig,"")</script>
<?php preg_replace("/([^0-9\.\-])/i";"";"-1,220,025.47 $"); ?>
Result : "-1220025.47"

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