Executing things you want to from streams

That’s what we need, sometimes!

Case

“I have a bunch of paths, and I want to pass them as arguments to a program!”

Well good news.

Example, find all readme.md files, and print them out:

find . | grep readme.md | xargs cat

(looks familiar)

More advanced

We may need to place an argument into a specific spot, we can use replacement to do that.

Use the -J flag to specify what you’d like to use as a replacement string (something that isn’t in your command you’re building….), and then build your command

echo hello | xargs -I % echo % world

Useful

Yes, but also SUPER dangerous. There’s some common things that can go horribly wrong/

What happens if your paths/inputs have spaces in them? It will be interpreted as two different inputs to your command. rm -rf /this\ and\ that is not the same as rm -rf /this and that (the latter removing the files /this, then the local files that, and). Quotes are your friend, in this case.

You need to break the quotes to make sure they get passed to xargs, rather than interpreted immediately. Consider the files Jean-Claude and the file with a space in it Van Damme.

$ ls
Jean-Claude  Van Damme
$ ls | xargs -I % echo rm \"%\"
rm "Jean-Claude"
rm "Van Damme"

Note the echo to try out the command before you run it. That lets you inspect the command you’ve built before running it.

Obviously you wouldn’t delete files this way, rm * would do. But could!

Executing one command per input

What if we want to run one command per input (remember that inputs are whitespace-separated)? Depending on what you’re hoping to pass the inputs to…

echo this that other | xargs -L 1 echo

Consider tar, you might want many tar files, not 1 huge tar file. So, you’d want to use -L 1 to pass each input to a single tar command.