How to match exclamation mark (!) in PHP?

Question

I want to match camel cased words beginning with ! such as !RedHat contained in $line. I'm using php 5.3.10-1ubuntu2 with Suhosin-Patch (cli).

I'm trying following things:

• $line = preg_replace(" !([A-Z])", " $1", $line);
  • result: PHP Warning: preg_replace(): No ending delimiter '!' found
• $line = preg_replace(" \!([A-Z])", " $1", $line);
  • result: PHP Warning: preg_replace(): Delimiter must not be alphanumeric or backslash
• $line = preg_replace(" [!]([A-Z])", " $1", $line);
  • result: PHP Warning: preg_replace(): Unknown modifier '('
• $line = preg_replace(" [\!]([A-Z])", " $1", $line);
  • result: PHP Warning: preg_replace(): Unknown modifier '('

How is the correct way to match ! in PHP regexp?

Answer 1

You need to use delimiters in your regex - non-alphanumeric, as the error message states:

$line = preg_replace("/ !([A-Z])/", " $1", $line);

Notice the / characters at the beginning and end of the regex string.

These don't have to be / - you could use # or even ! - but if you use ! then you'll need to escape the ! char inside the regex itself.