Question

In PHP I want to insert a white space after each < but only if there is no white space already.

I tried:

preg_replace('/<\S/', '< ', $data);

This works for a single < but if I have << it does not work anymore.

Answer 1

As @Summoner pointed out, your current regex replaces the character after a < with a space rather than inserting one. Well, both problems (the replacement and the code not working on something like <<) can be fixed with one solution: lookaheads. Try this code:

preg_replace('/<(?!\s)/', '< ', $data);