I found these things in my regex body but I haven't got a clue what I can use them for. Does somebody have examples so I can try to understand how they work?
(?=) - positive lookahead
(?!) - negative lookahead
(?<=) - positive lookbehind
(?<!) - negative lookbehind
(?>) - atomic group
Given the string foobarbarfoo:
bar(?=bar) finds the 1st bar ("bar" which has "bar" after it)
bar(?!bar) finds the 2nd bar ("bar" which does not have "bar" after it)
(?<=foo)bar finds the 1st bar ("bar" which has "foo" before it)
(?<!foo)bar finds the 2nd bar ("bar" which does not have "foo" before it)
You can also combine them:
(?<=foo)bar(?=bar) finds the 1st bar ("bar" with "foo" before it and "bar" after it)
(?=)Find expression A where expression B follows:
A(?=B)
(?!)Find expression A where expression B does not follow:
A(?!B)
(?<=)Find expression A where expression B precedes:
(?<=B)A
(?<!)Find expression A where expression B does not precede:
(?<!B)A
(?>)An atomic group exits a group and throws away alternative patterns after the first matched pattern inside the group (backtracking is disabled).
(?>foo|foot)s applied to foots will match its 1st alternative foo, then fail as s does not immediately follow, and stop as backtracking is disabledA non-atomic group will allow backtracking; if subsequent matching ahead fails, it will backtrack and use alternative patterns until a match for the entire expression is found or all possibilities are exhausted.
(foo|foot)s applied to foots will:
foo, then fail as s does not immediately follow in foots, and backtrack to its 2nd alternative;foot, then succeed as s immediately follows in foots, and stop.