Perform Multiple Operations in Linux with the ‘xargs’ Command

http://www.maketecheasier.com/mastering-xargs-command-linux

Xargs is a useful command that acts as a bridge between two commands, reading output of one and executing the other with the items read. The command is most commonly used in scenarios when a user is searching for a pattern, removing and renaming files, and more.
In its basic form, xargs reads information from the standard input (or STDIN) and executes a command one or more times with the items read.
As an illustration, the following xargs command expects the user to enter a file or a directory name:

xargs ls -l

Once a name is entered, the xargs command passes that information to the ls command.
Here is the output of the above shown xargs command when I executed it from my home directory by entering “Documents” (which is a sub-directory in my Home folder) as an input:

Observe that in this case, the xargs command executed the ls command with the directory name as a command line argument to produce a list of files present in that directory.
While the xargs command can be used in various command line operations, it comes in really handy when used with the find command. In this article, we will discuss some useful examples to understand how xargs and find can be used together.

Operations involving multiple files

Suppose you want to copy the contents of “ref.txt” to all .txt files present in a directory. While the task may otherwise require you to execute multiple commands, the xargs command, along with the find command, makes it simple.
Just run the following command:

find ./ -name "*.txt" | xargs -n1 cp ../ref.txt

To understand the command shown above, let’s divide it into two parts.
The first part is find ./ -name "*.txt" , which searches for all the .txt files present in the current directory.
The second part xargs -n1 cp ../ref.txt will grab the output of the first command (the resulting file names) and hand it over to the cp (copy) command one by one. Note that the -n option is crucial here, as it instructs xargs to use one argument per execution.
When combined together, the full command will copy the content of “ref.txt” to all .txt files in the directory.

Operations involving large number of arguments

One of the major advantages of using xargs is its ability to handle a large number of arguments. For example, while deleting a large number of files in one go, the rm command would sometimes fail with an “Argument list too long” error. That’s because it couldn’t simply handle such a long list of arguments. This is usually the case when you have too many files in the folder that you want to delete.

This can be easily fixed with xargs. To delete all these files, use the following command:

find ./rm-test/ -name "*" -print | xargs rm

Operations involving pattern search

Software developers as well as system administrators do a lot of pattern searching while working on the command line. For example, a developer might want to take a quick look at the project files that modify a particular variable, or a system administrator might want to see the files that use a particular system configuration parameter. In these scenarios, xargs, along with find and grep, makes things easy for you.
For example, to search for all .txt files that contain the “maketecheasier” string, run the following command:

$ find ./ -name "*.txt" | xargs grep "maketecheasier"

Here is the output the command produced on my system:

Cut/copy operations

Xargs, along with the find command, can also be used to copy or move a set of files from one directory to another. For example, to move all the text files that are more than 10 minutes old from the current directory to the previous directory, use the following command:

find . -name "*.txt" -mmin +10 | xargs -n1  -I '{}' mv '{}' ../

The -I command line option is used by the xargs command to define a replace-string which gets replaced with names read from the output of the find command. Here the replace-string is {}, but it could be anything. For example, you can use “file” as a replace-string.

find . -name "*.txt" -mmin 10 | xargs -n1  -I 'file' mv 'file' ./practice

How to tell xargs when to quit

Suppose you want to list the details of all the .txt files present in the current directory. As already explained, it can be easily done using the following command:

find . -name "*.txt" | xargs ls -l

But there is one problem; the xargs command will execute the ls command even if the find command fails to find any .txt file. Here is an example:

So you can see that there are no .txt files in the directory, but that didn’t stop xargs from executing the ls command. To change this behaviour, use the -r command line option:

find . -name "*.txt" | xargs -r ls -l

Conclusion

Although I’ve concentrated here on using xargs with find, it can also be used with many other commands. Go through the command’s main page to learn more about it, and leave a comment below if you have a doubt/query.