Perl is famous for its one-liners. By using the -e command line switch you can execute the script supplied as an argument. But the real power comes when you use -p (to process each line of a supplied file), and -i (to modify the file in place). The classic example is to perform search and replace on a bunch of files. The following will replace all occurrences of curious george with the gruffalo:

perl -pi -e 's/curious george/the gruffalo/g' favourites.html

I was happy to learn recently that you can do the same with Groovy. Groovy supports the same set of command line arguments, but the script is obviously more Java-ish (the =~ operator is a Groovy regex operator):

groovy -pi -e "(line =~ 'curious george').replaceAll('the gruffalo')" favourites.html

OK, it's not quite as terse, but it's still a one-liner. (Actually, there is a bug in the latest version of Groovy, JSR 1, which prevents the -i switch from functioning correctly. Hopefully it will be fixed soon. As a workaround you can call groovy -pi.bak -e ... which has the same effect and in addition backs up the original file.)

More complicated examples provide a great way to learn more about Groovy features. This awk-like replacement prints the first and penultimate whitespace-separated columns from a text file, and shows off Groovy's Python-inspired slicing ability.

groovy -pe "line.split('\\s')[0, -2]" *

And this will find duplicate words:

groovy -ne "if (line =~ '\\b(\\w+)\\b\\s+\\b\\1\\b') println line" *

Do you have any Groovy one-liners?