linux - Is d not supported by grep's basic expressions?

Question

This does not generate any output. How come?

$ echo 'this 1 2 3' | grep 'd+'

But these do:

$ echo 'this 1 2 3' | grep 's+'
this 1 2 3

$ echo 'this 1 2 3' | grep 'w+'
this 1 2 3

Answer 1

grep's default mode is (iirc) POSIX regex, and d is pcre. You can either pass -P to gnu grep, for perl-like regexps, or use [[:digit:]] instead of d.

daenyth@Bragi ~ $ echo 1 | grep -P 'd'
1
daenyth@Bragi ~ $ echo 1 | grep '[[:digit:]]'
1