Regex: Use start of line/end of line signs (^ or $) in different context
While doing some small regex task I came upon this problem. I have a string that is a list of tags that looks e.g like this:foo,bar,qux,garp,wobble,thud
What I needed to do was to check if a certain tag, e.g. 'garp' was in this list. (What it finally matches is not really important, just if there is a match or not.)
My first and a bit stupid try at this was to use the following regex:[^,]garp[,$]
My idea was that before 'garp' there should either be the start of the line/string or a comma, after 'garp' there should be either a comma or the end of the line/string.
Now, it is instantly obvious that this regex is wrong: Both ^ and $ change their behaviour in the context of the character class [ ].
What I finally came up with is the following:^garp$|^garp,|,garp,|,garp$
This regex just handles the 4 cases one by one. (Tag at beginning of list, in the center, at the end, or as the only element of the list.) The last regex is somehow a bit ugly in my eyes and just for funs sake I'd like to make it a bit more elegant.
Is there a way how the start of line/end of line characters (^ and $) can be used in the context of character classes?
EDIT: Ok, some more info was wished so here it is: I'm using this within an Oracle SQL statement. This sadly does not allow any look-around assertions but as I'm only interested if there is a match or not (and not what is matched) this does not really affect me here. The tags can contain non-alphabetical characters like - or _ so \bgarp\b would not work. Also one tag can contain an other tag as SilentGhost said, so /garp/ doesnt work either.
You can't use ^ and $ in character classes in the way you wish - they will be interpreted literally, but you can use an alternation to achieve the same effect:
(^|,)garp(,|$)
you just need to use word boundary (\b) instead of ^ and $:
\bgarp\b
Just use look-arounds to solve this:
(?<=^|,)garp(?=$|,)
The difference with look-arounds and just regular groups are that with regular groups the comma would be part of the match, and with look-arounds it wouldn't. In this case it doesn't make a difference though.