I find this much more useful than sed.
Example 1: Filter/regex. Print numbers from matching lines.
foo 12 bar 23 other baz 34
-e is script mode. -n loops over your input automatically.
# -n option does the while loop for you horse:~ adam$ perl -ne 'print "$1\n" if /(\d+)/' foo.txt 12 23 34
Without the -n option you’d have to add your own while loop.
perl -e 'while(<>) { print "$1\n" if /(\d+)/ }' foo.txt
12
23
34
Example 2: Modify. Wrap all numbers. -p loops around and prints the value of the substitution – much like sed
perl -pe 's/(\d+)/#$1#/' foo.txt foo #12# bar #23# other baz #34#
