How to match a pound (#) symbol at the beginning of a word using regex in PHP

Question

I need a regex to match a word that starts with #.

I wrote this question How to match a pound (#) symbol in a regex in php (for hashtags), but I forgot to explain that I need the # at the beginning of a word.

I need to match #word, #123, #12_sdas, but not 1#234 or #1234.

For example, in "#match1 notMatch not#Match #match2 notMatch #match3", only #match1, #match2 and #match3 should appear.

Edit: I just want one pound (#), followed by one or more [a-ZA-Z0-9_]. The match can't have any of [a-ZA-Z0-9_] before.

My problem was finding the pound at the beginning of the word.

I think you need to give a clearer explanation what exactly should be matched. It's not clear in which cases numbers are allowed. (e.g. why match #123 but not #1234) — s1lence, Feb 23 '12 at 23:56

bluepnume · Answer 1 · 2012-02-23T23:02:36.543

4

preg_match_all('/(?:^|\s)(#\w+)/', $string, $results);

EDIT: don't have a php cli to test this, but the regex works in python at the very least.

edited Feb 23 '12 at 23:02

answered Feb 23 '12 at 22:53

bluepnume

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this does not need the hashsymbol to be at the very beginning of a word... – s1lence Feb 23 '12 at 22:55
Does now! Sorry, missed that requirement. – bluepnume Feb 23 '12 at 22:57
1

+1 before i realized it should not match #1234 – Aprillion Feb 23 '12 at 23:50
2

I have no idea why it should match #123 but not #1234... – bluepnume Feb 24 '12 at 00:08
+1 this, accepted the one over this. It can match #1234 if it comes after a non \w char. The regex is fine, but the one over separates the hashtag with the # and without it ($match returns #tag and tag in positions 0 and 1 respectively). – J-Rou Feb 24 '12 at 16:28

s1lence · Accepted Answer · 2012-02-25T13:16:56.400

1

Try this:

preg_match_all('/(?:^|\s+)(#\w+)/', $your_input, $your_results);
// print results
print_r($your_results);

It will match all words beginning with a # symbol. Words can be sepearted by all valid whitespace characters (so one of \t\r\n\v\f)

Example

//input
#match1 notMatch not#Match #match2 notMatch #match3
//output
Array
(
    [0] => Array
        (
            [0] => #match1
            [1] =>  #match2
            [2] =>  #match3
        )

    [1] => Array
        (
            [0] => #match1
            [1] => #match2
            [2] => #match3
        )

)

edited Feb 25 '12 at 13:16

answered Feb 23 '12 at 22:54

s1lence

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The `^` at the start of your regex requires space and will only work on tags at the start .. I think you want `/(?:^|\s+)#(\w+)/'` – Explosion Pills Feb 23 '12 at 22:56
Not working. Its not detecting nothing – J-Rou Feb 23 '12 at 23:01
fixed the regex to match at line beginnings. And added sample output. – s1lence Feb 23 '12 at 23:05
php 8.1 - not working properly subject 'asdas ###ewewe #767 # tata # zbiuta' result is array repeted twice with result #767 – zoore Feb 21 '23 at 19:29

How to match a pound (#) symbol at the beginning of a word using regex in PHP

2 Answers2