On Tue, Jul 10, 2018 at 10:02:34AM -0300, Paulo Marcel Coelho Aragão wrote: > It baffles me that literal \< \> are not evaluated correctly > > paulo:~$ [[ 'foo bar' =~ \<foo\> ]] && echo yes || echo no > no
In this context, the backslashes serve only to "quote" the less-than and greater-than signs. It's just like writing [[ 'foo bar' =~ "<"foo">" ]] And when you quote a character on the right-hand side of = or =~ inside a [[ command, that character LOSES whatever specialness it might have had in that context. In order to put a backslash-that-acts-like-a-backslash-to-the-regex-engine inside the RE on the right-hand side of =~ you need to put the RE into a variable. (Normally this is not a problem because normally you write POSIX ERE-compliant regexes because that's all that you can count on, and POSIX EREs don't use backslashes to turn features ON. Only to turn them OFF.) > Empirically all this demonstrates: > > 1. bash recognizes \< \> \b as word anchors Only on some systems. Not on others. So don't do that. > 2. bash doesn't evaluate them correctly when used as literals > 3. bash evaluates them correctly when used with parameter expansion Which is one of the reasons it is STRONGLY encouraged to put your RE into a variable and then use =~ $var. (Another reason is backward compatibility with bash 3.x versions, should you happen to care about that.)
