What flavour of regular expression is grep?
grep
Solution
Default GNU `grep` behavior is to use a slightly flavorful variant on POSIX basic regular expressions, with a similarly tweaked species of POSIX extended regular expressions for `egrep` (usually an alias for `grep -E`). POSIX ERE is what PHP `ereg()` uses.
GNU `grep` also claims to support `grep -P` for PCRE, by the way. So no terribly special kind of `grep` required.
Problem
I'm guessing it's not a Perl Compatible Regular Expression, since there's a special kind of `grep` which is specifically PCRE. What's `grep` most similar to? Are there any special quirks of `grep` that I need to know about? (I'm used to Perl and the `preg` functions in PHP)