My company uses FreeBSD, and therefore FreeBSD's flavor of make.
A few of our in-house ports include something like this (where BRANCH is something that came from an SVN URL, either 'trunk' or a branch name like 'branches/1.2.3').
PORTVERSION= ${BRANCH:C,^branches/,,}
The Variable modifiers section of make(1) documents the :C colon-c modifier as
:C/pattern/replacement/[1gW]
Am I looking at the right documentation? ^branches/ looks like a regex pattern to me, but it looks like the actual code uses , instead of / as a separator. Did I skip documentation explaining that?
The documentation says:
:C/pattern/replacement/[1gW]The :C modifier is just like the :S modifier except that the old and new strings, instead of being simple strings, are an extended regular expression (see regex(3)) string pattern and an ed(1)-style string replacement.
and in :S:
Any character may be used as a delimiter for the parts of the modifier string.
As @MadScientist pointed out, it's quite common to use a different delimiter, especially when / is a part of pattern or replacement string, like in your case. Otherwise it would require escaping and would look like ${BRANCH:C/^branches\///} which seems less readable.