Let's suppose I have an RGB string (format: #<2 hex digits><2 hex digits><2 hex digits>) like this:
"#00BBCC"
and I'd like to match and capture its <2 hex digits> elements in a more compact manner than by using the obvious:
"#\\([[:xdigit:]\\{2\\}]\\)\\([[:xdigit:]\\{2\\}]\\)\\([[:xdigit:]\\{2\\}]\\)"
I've tried:
"#\\([[:xdigit:]]\\{2\\}\\)\\{3\\}"
and:
"#\\(\\([[:xdigit:]]\\{2\\}\\)\\{3\\}\\)"
But the most they matched has been the first <2 hex digits> element.
Any idea? Thank you.
If you want to capture R,G,B in different subgroups, so that you can extract them using (match-string group), you need to have three different parentheses groups in your regexp at some point.
\(...\)\(...\)\(...\)
Otherwise, if you use a repeat pattern such as
\(...\)\{3\}
you have only one group, and after the match it will only contain the value of the last match. So, say, if you have something along the lines of
\([[:xdigit:]]\{2\}\)\{3\}
it will match a string like "A0B1C2", but (match-string 1) will only contain the contents of the last match, i.e. "C2", because the regexp defines only one group.
Thus you basically have two options: use a compact regexp, such as your third one , but do some more substring processing to extract the hex number as Sean suggests, or use a more complex regexp, such as your first one, which lets you access the three sub-matches more conveniently.
If you're mostly worried about code readability, you could always do something like
(let ((hex2 "\\([[:xdigit:]]\\{2\\}\\)"))
(concat "#" hex2 hex2 hex2))
to construct such a more complex regexp in a somewhat less redundant way, as per tripleee's suggestion.