How to use the Linux xargs command

The xargs command in Linux is a versatile utility that transforms input from standard input (stdin) into arguments for a specified command. It’s an invaluable tool for streamlining command-line workflows, especially when dealing with lists of items. In this guide, we’ll explore the basics of xargs with simple examples and then dive into practical use cases related to Docker.

Understanding xargs Basics

At its core, xargs is designed to build and execute commands from standard input. Let’s begin with some straightforward examples to grasp the fundamentals.

Simple Example 1: Concatenating Strings

Consider a scenario where you want to concatenate a list of strings into a single line:

echo "apple banana orange" | xargs

This command outputs:

apple banana orange

Simple Example 2: Echoing Each Word on a New Line

To echo each word on a new line, use the -n option:

echo "apple banana orange" | xargs -n 1

This produces:

apple
banana
orange

Now that we’ve covered the basics, let’s explore how xargs can be applied in a Docker-related context.

xargs and Docker: Practical Examples

Example 1: Removing Docker Containers

Suppose you have running Docker containers that you want to stop and remove. You can leverage xargs to streamline this process:

docker ps -q | xargs docker stop

This command extracts the IDs of running containers (docker ps -q) and stops each one using xargs.

docker ps -q | xargs docker rm

Similarly, this command removes the stopped containers.

Example 2: Building Docker Images

Consider a scenario where you have multiple directories, each containing a Dockerfile, and you want to build Docker images from these Dockerfiles. xargs can assist in simplifying this task:

ls -d */ | xargs -I {} docker build -t {}

Here, ls -d */ lists all directories in the current location, and xargs -I {} utilizes each directory name as an argument for the docker build command.