perl

The Perl 5 language interpreter. More information: https://www.perl.org.

• Print lines from stdin [m/] matching regex1 and case insensitive [/i] regex2:

perl -n -e 'print if m/regex1/ and m/regex2/i'

• Say [-E] first match group, using a regexp, ignoring space in regex [/x]:

perl -n -E 'say $1 if m/before ( group_regex ) after/x'

• [-i]n-place, with backup, [s/] substitute all occurrence [/g] of regex with replacement:

perl -i'.bak' -p -e 's/regex/replacement/g' path/to/files

• Use perl's inline documentation, some pages also available via manual pages on Linux:

perldoc perlrun ; perldoc module ; perldoc -f splice; perldoc -q perlfaq1