PHP Regex: match character set OR end of string

Question

I am porting code from Node.js to PHP and keep getting errors with this regular expression:

^/[a-z0-9]{6}([^0-9a-z]|$)

PHP complains about a dollar sign:

Unknown modifier '$'

In JavaScript I was able to check if a string was ending with [^0-9a-z] or END OF STRING. How do I do this in PHP with preg_match()?

My PHP code looks like this:

<?
    $sExpression = '^/[a-z0-9]{6}([^0-9a-z]|$)';
    if (preg_match('|' . $sExpression .  '|', $sUrl)) { 
        // ... 
    }
?>

The JavaScript code was similar to this:

var sExpression = '^/[a-z0-9]{6}([^0-9a-z]|$)';
var oRegex      = new RegExp(sExpression);
if (oRegex.test(sUrl)) { 
    // ... 
}

$ has a special meaning in regex. You have to escape that. — Havenard
– Havenard, Commented Jul 8, 2014 at 5:17
what php function are you using such as preg_match, preg_match_all, and well you do have this error "/[" literal "[" not character group. ^/[a-z0-9]{6}([^0-9a-z]|$) — ArtisticPhoenix
– ArtisticPhoenix, Commented Jul 8, 2014 at 5:18

Peter Mortensen · Accepted Answer · 2023-01-03 16:11:46Z

6

To match a string that starts with a slash, followed by six alphanumerics and is then followed by either the end-of-string or something that's not alphanumeric:

preg_match('~^/[a-z0-9]{6}([^0-9a-z]|$)~i', $str);

The original JavaScript probably used new RegExp(<expression>), but PCRE requires a proper enclosure of the expression; those are the ~ characters I've put in the above code. Btw, I've made the expression case insensitive by using the i modifier; feel free to remove it if not desired.

You were using | as the enclosure; as such, you should have escaped the pipe character inside the expression, but by doing so you would have changed the meaning. It's generally best to choose delimiters that do not have a special meaning in an expression; it also helps to choose delimiters that don't occur as such in the expression, e.g., my choice of ~ avoids having to escape any character.

Expressions in PCRE can be generalised as:

<start-delimiter> stuff <end-delimiter> modifiers

Typically, the starting delimiter is the same as the ending delimiter, except for cases such as [expression]i or {expression}i whereby the opening brace is matched with the closing brace :)

edited Jan 3, 2023 at 16:11

Peter Mortensen

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answered Jul 8, 2014 at 5:22

Ja͢ck

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4 Comments

Lex Podgorny Over a year ago

Jack, you are right, I should have shown the complete code – I am using "|" character as delimiter. So, I guess this is not the problem. Please see my edit in the question.

Havenard Over a year ago

Yes it is the problem because your delimiter | is also part of your expression, this is why it thinks $ is a flag, because it is right after a |.

Ja͢ck Over a year ago

@LexPodgorny Well, yeah, the expression itself is fine (I think).

Lex Podgorny Over a year ago

You are absolutely right. Changing | to ~ fixed it. Thank you for taking time to explain!

Peter Mortensen · Accepted Answer · 2023-01-03 16:15:17Z

0

Fix the regular expression first:

^/[a-z0-9]{6}([^0-9a-z]|$)

Try this.

As others pointed out, I'm an idiot and saw a / as a \ ... LOL.

Ok, well go at this again,

I’d avoid using the "|" and just do it this way.

if (preg_match('/^\/[a-z0-9]{6}([^0-9a-z]|$)/', $sUrl)) { ... }

edited Jan 3, 2023 at 16:15

Peter Mortensen

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answered Jul 8, 2014 at 5:19

ArtisticPhoenix

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9 Comments

ArtisticPhoenix Over a year ago

really, you think that is a valid regx?

Havenard Over a year ago

I don't see how ^/ is valid either. Last I checked it was /^.

ArtisticPhoenix Over a year ago

so a character group implied by {6} without an opening bracket is good syntax? shoot. lol @ me tired, I saw / as \ but still he needs to escape it surly

ArtisticPhoenix Over a year ago

@zerkms - i'll blame that on dyslexia, but what is his delimiters is now the question.

Havenard Over a year ago

He updated his question finally showing what was causing all this confusion. It turns out / wasn't meant to be the delimiter.

|

Peter Mortensen · Accepted Answer · 2023-01-03 16:19:00Z

0

Reducing this to just matching a particular character or end of string (PHP),

\D777(\D|$)\

This will match:

xxx777xxx or xxx777 but not xxx7777 or xxx7777xxx

edited Jan 3, 2023 at 16:19

Peter Mortensen

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answered Oct 12, 2018 at 9:00

zzapper

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1 Comment

mickmackusa Over a year ago

\D will only match a single non-digital character. Those xxx are misleading.

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