PHP regex: find the first occurrence of a given pattern in a string

Question

my string can be

new-york-10036

or

chicago-55036

the desired result is

new-york
chicago

and i basically want to remove all the string that come after the first dash - followed by a number

seems easy but i don't know how

This one should be enough (.*)-\d+ regex101.com/r/mY6fW3/2 — Axalix
– Axalix, Commented Mar 4, 2016 at 0:31
You already have a good start with this: "i basically want to remove all the string that come after the first dash - followed by a number" now you can try to put it into a more general pseudo regex, like: [Anything]-number(s), which you then can try to translate step by step into a regex like: (.*)-\d+ — Rizier123
– Rizier123, Commented Mar 4, 2016 at 0:58
pretty sure this would work with preg_match_all: /([a-zA-Z\-]+)\-[0-9]+/g — hanshenrik
– hanshenrik, Commented Mar 4, 2016 at 1:00

tayllan · Accepted Answer · 2016-03-04 01:18:20Z

3

You can use Negative Lookahead, like so:

(.+)(?=\-\d)

The regex reads: "get me everything that is not followed by exactly one dash and exactly one number after that".

Given the input new-york-10036 the regex is going to capture only new-york. In PHP you can get the matched string with:

$string = 'new-york-10036';

$regex = '/(.+)(?=\-\d)/';

preg_match($regex, $string, $return);

echo $return[0] . "\n";

It outputs new-york.

See the regex working here.

edited Mar 4, 2016 at 1:18

answered Mar 4, 2016 at 0:27

tayllan

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7 Comments

Francesco Over a year ago

does the "d" stands for number?

tayllan Over a year ago

@Francesco actually, it's the \d, which stands for "a number between 0 and 9". It's the same as [0-9] and is called a "character class", which you can see here.

Rizier123 Over a year ago

@Francesco Yes, \d == [0-9], but you can probably better remember it with digit

Rizier123 Over a year ago

@Francesco preg_match !== preg_match_all

Francesco Over a year ago

my question was about PHP: given the regex, how do i extract the string?

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