Question

This seems like it should be dirt simple, but the awk gensub/gsub/sub behavior has always been unclear to me, and now I just can’t get it to do what the documentation says it should do (and what experience with a zillion other similar tools suggests should work). Specifically, I want to access “captured groups” from a regex in the replacement string. Here’s what I think the awk syntax should be:

awk '{ gsub(/a(b*)c/, "Here are bees: \1"); print; }'

That should turn “abbbc” into “Here are bees: bbb”. It does not, at least not for me in Ubunutu 9.04. Instead, the “\1” is rendered as a ^A; that is, the character with code 1. Not what I want, of course. How do I do this?

Thanks.

Answer 1

With GNU awk:

echo abbc | awk '{ print gensub(/a(b*)c/, "Here are bees: \\1", "g", $1);}'

See manual here to see the difference between gsub and gensub

gensub() provides an additional feature that is not available in sub()
or gsub(): the ability to specify components of a regexp in the
replacement text. This is done by using parentheses in the regexp to
mark the components and then specifying ‘\N’ in the replacement text,
where N is a digit from 1 to 9.