Question

I know I can use preg_match but I was wondering if php had a way to evaluate to a regular expression like:

if(substr($example, 0, 1) == /\s/){ echo 'whitespace!'; }

Answer 1

PHP does not have first-class regular expressions.

You will need to use the functions provided by the default PCRE extension. Sorry. It’s a backslash-escaping nightmare, but it’s all we’ve got.

(There’s also the now-deprecated POSIX regex extension, but you should not use them any longer. They are slower, less featureful, and most important, they aren’t Unicode-safe. Modern PCRE versions understand Unicode very well, even if PHP itself is ignorant about it.)

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With regard to the backslash-escaping nightmare, you can keep the horror to a minimum by using single quotes to enclose the string containing the regex instead of doubles, and picking an appropriate delimiter. Compare:

"/^http:\\/\\/www.foo.bar\\/index.html\\?/"

versus

'!^http://www.foo.bar/index.html\?!'

Inside single quotes, you only need to backslash-escape backslashes and single quotes, and picking a different delimiter avoids needing to escape the delimiter inside the regex.