xargs

Shell (~bash)

So, you want to sling command line like a boss, eh? I’ve heard it said and believe it more and more each day that the core things you should learn on the command line are find, xargs, grep, sed, cut, while, and echo. (add wc, sort, and history to taste)

Of these, the one I see ignored most often is xargs. So, let’s check it out:

>xargs
1
2
3
4
^D
1 2 3 4

Technically, xargs “reads space, tab, newline and end-of-file delimited strings from the standard input and executes a command with the strings as arguments”…and the default command is echo.

So, in the above, we invoke xargs, it starts listening to stdin, we provide a list of numbers separated by newlines, ^D signals the end of the input, and xargs turns our numbers into a space-separated list that gets passed to echo. Voila!

We could also separate things with tabs or spaces. We can even mix them:

>xargs
1
2 3
4	5
^D
1 2 3 4 5

In practice, xargs usually takes a list of things generated by some other command (like find) and iterates a command over them. What if we wanted to delete all the files larger than 100MB in the current directory tree?

>find . -size 100M | xargs rm

(If you’re really worried that this will hiccup on filenames with a space in them, you can use find -print0 and xargs -0 instead. Those create/consume null delimited lists instead. In practice, I’ve never had that be a problem.)

What if we wanted to clean up our project a little bit?

>find . -name *.o | xargs rm -rf

…and so on…

CAUTION: It’s really easy to combine find, xargs, and rm in clever ways that will do terrible things to your system. Measure twice, rm once.