Simple error in php regex preg_match

Question

I think I've been staring at php too long, I cannot for the life of me figure out why this doesn't work.

I'm trying to match phone numbers with this format (555.555.5555).

if (preg_match("[0-9]{3}.[0-9]{3}.[0-9]{4}", "555.555.5555", $matches)){
    echo matches[0];
}

My first thought is I wonder if the . need escaped first or I am just missing something incredibly simple

Reeno · Accepted Answer · 2014-01-22 17:15:12Z

2

You need a delimiter for the regex, like e.g. / or #. A delimiter is used to separate the regex from possible modifiers.

if (preg_match("/[0-9]{3}\.[0-9]{3}\.[0-9]{4}/", "555.555.5555", $matches)){
    echo matches[0];
}

I also changed the dots to \. since . is every character (besides a new line, thanks to @Amal Murali in the comments), \. is only a dot.

edited Jan 22, 2014 at 17:15

answered Jan 22, 2014 at 17:08

Reeno

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5 Comments

ladyoftime315 Over a year ago

I had seen that in a few examples and wondered if that was my issue. It didn't show up in all the examples, so what is the purpose of the / and why would I need it?

Reeno Over a year ago

It tells the parser, where the regex starts and ends. You can add some modifiers after the closing delimiter, like described on php.net/manual/en/reference.pcre.pattern.modifiers.php

ladyoftime315 Over a year ago

Thanks a lot, simple enough.

Amal Over a year ago

Small nitpick: . matches every character EXCEPT a new line.

Reeno Over a year ago

Thanks @AmalMurali, I added it to my answer

Amal · Accepted Answer · 2014-01-22 17:09:22Z

1

If not escaped, the dot character (.) matches any character (except a new line). If you want to match a literal . character, you need to escape it with backslash - so you'll need to write \.

You also need to wrap it in valid delimiters, like /. A delimiter can be any non-alphanumeric, non-backslash, non-whitespace character. ~, #, / etc are some of the most commonly used delimiters. I'm using a forward slash here:

if (preg_match("/[0-9]{3}\.[0-9]{3}\.[0-9]{4}/", "555.555.5555", $matches)){
    echo $matches[0];
}

Output:

555.555.5555

answered Jan 22, 2014 at 17:09

Amal

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