Let’s say you have a text file which you wish to use an input to some command-line tool. Specifically, the goal is to apply the same command to each line in the file. This short post showcases how this can be done in a Unix shell (such as Bash) using a combination of cat, xargs and piping.

As a motivating example, consider a file repos.txt containing URLs of several Github repositories, and our goal is to clone each of the repositiries. As such, the content of repos.txt can be the following:

https://github.com/semeniuta/EPypes.git
https://github.com/semeniuta/visionfuncs.git
https://github.com/semeniuta/pdata.git

Our goal is to clone each of those, i.e. execute the usual git clone <URL> command. As a first step, let’s just print the content of the file in the terminal. This is done with the cat command:

cat repos.txt

In order to automatically pipe each line as an argument to the git clone command, the previus basic example is extended as follows:

cat repos.txt | xargs -L1 git clone

What is done here is that the entire standard output of cat is piped to the standard input of xargs. The latter uses this input as text that is inserted immediately after the specified command (git clone). The option -L1 instructs xargs to use at most 1 nonblank input line per command line, which guarantees that in our case the git clone command is executed three times, each time cloning the respective repository specified in the repos.txt file.