PHP Regex Expression isn't working. Issue with Backslashes?

Question

Regular expression in question:

$reg = '/[.]{1,}[\/\\]/';
if(preg_match($reg, $dir))...

I've tested this expression on http://regexpal.com and http://regex.larsolavtorvik.com/ it worked fine, but in my PHP script I'm getting this notification.

Message: preg_match() [function.preg-match]: Compilation failed: missing terminating ] for character class at offset 12

I've messed around with the number of '\', but it hasn't changed anything. Any suggestions on what might be going wrong?

I've tried to look for similar issues, but all I seem to run into is people who haven't added delimiters.

Yeah, this one's kind of confusing. See this answer: stackoverflow.com/a/2145823/1382779 — Nathanael
– Nathanael, Commented Aug 8, 2012 at 19:20

Madara's Ghost · Accepted Answer · 2012-08-08 19:51:45Z

4

That's because \\ will be escaped by PHP to a single \, which will make preg_match evaluate your patterns as

/[.]{1,}[\/\]/

To have 2 backslashes in PHP string, you'll need to actually type 4:

$reg = '/[.]{1,}[\/\\\\]/';
preg_match($reg, "test");

Or use PHP's heredoc:

$reg = <<<REGEX
/[.]{1,}[\/\\\\]/
REGEX;
preg_match($reg, "test");

EDIT: seems like Heredoc also requires 4 backslashes. That's because of control characters like \n.

answered Aug 8, 2012 at 19:22

Madara's Ghost

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