What flavour of regular expression is grep?

Question

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 simil

Answer 1

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.