Range out of order in character class

Question

I\'m getting this odd error in the preg_match() function:

Warning: preg_match(): Compilation failed: range out of order in character class at offset 54

The l

Answer 1

If $gsmNumber contains a square bracket, backslash or various other special characters it might trigger this error. If that's possible, you might want to validate that to make sure it actually is a number before this point.

Edit 2016:

There exists a PHP function that can escape special characters inside regular expressions: preg_quote().

Use it like this:

preg_match(
  '/<!--GSM\sPER\sNUMBER\s-\s' .
  preg_quote($gsmNumber, '/') . '\s-\sSTART-->(.*)<!--GSM\sPER\sNUMBER\s-\s' .
  preg_quote($gsmNumber, '/') . '\s-\sEND-->/s', $fileData, $matches);

Obviously in this case because you've used the same string twice you could assign the quoted version to a variable first and re-use that.