POSIX Regular Expressions
POSIX regular expression are powerful, but compared to Perl regular expressions they are limited.
For example if you want to negate a filter using when using grep you cannot express this unless your pattern is a class.
This command lists all available and installable Perl versions offered by perlbrew`
$ perlbrew available
perl-5.32.0-RC1
perl-5.30.3
perl-5.28.3
perl-5.26.3.tar.bz2
perl-5.26.3
perl-5.24.4
i perl-5.22.4
perl-5.22.4.tar.bz2
perl-5.20.3
perl-5.20.3.tar.bz2
perl-5.18.4.tar.bz2
perl-5.18.4
perl-5.16.3.tar.bz2
perl-5.16.3
i perl-5.14.4
perl-5.14.4.tar.bz2
perl-5.12.5.tar.bz2
perl-5.12.5
i perl-5.10.1
perl-5.10.1.tar.bz2
i perl-5.8.9
perl-5.8.9.tar.bz2
perl-5.6.2
perl5.005_03
perl5.004_05
cperl-5.29.2
cperl-5.30.0
cperl-5.30.0-RC1
Since I am not interested in the *.bz2 listings, I want to filter listing matching this pattern:
$ perlbrew available | grep --regexp="\.tar\.bz2" --invert-match
perl-5.32.0-RC1
perl-5.30.3
perl-5.28.3
perl-5.26.3
perl-5.24.4
i perl-5.22.4
perl-5.20.3
perl-5.18.4
perl-5.16.3
i perl-5.14.4
perl-5.12.5
i perl-5.10.1
i perl-5.8.9
perl-5.6.2
perl5.005_03
perl5.004_05
cperl-5.29.2
cperl-5.30.0-RC1
cperl-5.30.0
I match the pattern and invert the match using grep option.
The above recipe is used in my Bash completion for perlbrew.