xargs is a pretty cool command. Lets say you have a sweet one-liner that returns a list of files you want to do something with; for example, like coping files from one directory to another. You can do this with just cp by itself, I am sure, but I would rather be safe and pipe to my hearts desires until I get exactly what I want. In this case, and with xargs, you can do just that…

Usage

Let me explain the usage example below as it was my first experience using xargs. I wanted to put together a kernel upgrade package, and I wanted to pull all the kernel files for a specific version into a central location so I could work from there and not mess with anything in my repo. The below command was used to grep for the files I wanted:

$ ls | grep '2.6.32-358.23' | grep -v 'python'
kernel-2.6.32-358.23.2.el6.x86_64.rpm
kernel-debug-2.6.32-358.23.2.el6.x86_64.rpm
kernel-debug-devel-2.6.32-358.23.2.el6.x86_64.rpm
kernel-devel-2.6.32-358.23.2.el6.x86_64.rpm
kernel-firmware-2.6.32-358.23.2.el6.noarch.rpm
kernel-headers-2.6.32-358.23.2.el6.x86_64.rpm
perf-2.6.32-358.23.2.el6.x86_64.rpm

Yeah, yeah… not extremely sophisticated; I am sure many know how to grep and -v grep. At this point I was like, great… I have my list of files, and now I want to copy them somewhere so I can begin to work with them safely separated from my repo.

xargs command can be used to run a command from standard input. To copy the list of files above to the /tmp directory:

$ ls | grep '2.6.32-358.23' | grep -v 'python' | xargs -I -t cp {} /tmp
cp kernel-2.6.32-358.23.2.el6.x86_64.rpm /tmp
cp kernel-debug-2.6.32-358.23.2.el6.x86_64.rpm /tmp
cp kernel-debug-devel-2.6.32-358.23.2.el6.x86_64.rpm /tmp
cp kernel-devel-2.6.32-358.23.2.el6.x86_64.rpm /tmp
cp kernel-firmware-2.6.32-358.23.2.el6.noarch.rpm /tmp
cp kernel-headers-2.6.32-358.23.2.el6.x86_64.rpm /tmp
cp perf-2.6.32-358.23.2.el6.x86_64.rpm /tmp

Lets talk about the -I and -t option briefly passed as arguments above…

The -I option by default replaces {} with the output, one line at a time, in its place, and the -t option prints the output rather than executing the command.

ls of temp

$ ls /tmp | grep '2.6.32-358.23'
kernel-2.6.32-358.23.2.el6.x86_64.rpm
kernel-debug-2.6.32-358.23.2.el6.x86_64.rpm
kernel-debug-devel-2.6.32-358.23.2.el6.x86_64.rpm
kernel-devel-2.6.32-358.23.2.el6.x86_64.rpm
kernel-firmware-2.6.32-358.23.2.el6.noarch.rpm
kernel-headers-2.6.32-358.23.2.el6.x86_64.rpm
perf-2.6.32-358.23.2.el6.x86_64.rpm

Referenced commands: cp, grep