Question

I’m looking for a regex that will scan a document to match a function call, and return the value of the first parameter (a string literal) only.

The function call could look like any of the following:

MyFunction("MyStringArg");

MyFunction("MyStringArg", true);

MyFunction("MyStringArg", true, true);

I’m currently using:
$pattern = '/Use\s*\(\s*"(.*?)\"\s*\)\s*;/';

This pattern will only match the first form, however.

Thanks in advance for your help!

Update
I was able to solve my problem with:
$pattern = '/Use\s*\(\s*"(.*?)\"/';

Thanks Justin!

~Scott

Answer 1

If you only care about the value of the first parameter, you can just chop off the end of the regex:

$pattern = '/Use\s*\(\s*"(.*?)\"/';

However, you should understand that this (or any pure-regex solution for this problem) will not be perfect, and there will be some possible cases it handles incorrectly. In this case, you’ll get false positives, and escaped quotes (\") will break it.

You can ignore escaped quotes by complicating it a bit:

$pattern = '/Use\s*\(\s*"(.*?)(?!<(?:\\\\)*\\)\"/';

This ignores " characters inside the quoted string if they have an odd number of backslashes in front of them.

However, the false-postives issue can’t be helped without introducing false-negatives, and vice versa. This is because PHP is an irregular language, so it can’t be parsed with “pure” regex, and even modern regex engines that allow recursion are going to need some pretty complex code to do a really thorough job at this.

All I’m saying is, if you’re planning a one-off job to quickly scrape through some PHP you wrote yourself, regex is probably fine. If you’re looking for something robust and open-ended that will do this on arbitrary PHP code, you need some kind of reflection or PHP parser.