Shell Command xargs
Introduction
xargs is a command that reads data from the standard input and executes a command with the data as arguments. It is used to build and execute command lines from standard input.
Usage
Normally when we want to create a file with a specific name, we would do something like this:
touch NewFile.txt
With xargs, we can do the same thing:
echo "NewFile.txt" | xargs touch
Differences between xargs and pipe
In Linux, pipe is used to connect the output of one command to the input of another command. For example, we can use ls to list all files in the current directory, and then use grep to filter the files that contain a specific string. The following command will list all files that contain the string test:
ls | grep test
This works when the second command accepts standard input. However, if the second command does not accept standard input, e.g. touch we need to use xargs to parse the content into argument list.
For example:
# if you echo new filename and pipe to touch
# it will prompt error
$ echo "NewFile" | touch
usage: touch [-A [-][[hh]mm]SS] [-achm] [-r file] [-t [[CC]YY]MMDDhhmm[.SS]]
[-d YYYY-MM-DDThh:mm:SS[.frac][tz]] file
# This happens when the second command does not accept standard input
# touch is a command that only accepts filename as argument
# Correct Usage:
$ touch "NewFile.txt"
# Using xargs to transform the content into argument list
$ echo "NewFile.txt" | xargs touch
Another Example is wc:
# if you echo a string and pipe to wc
$ echo "hello world" | wc
1 2 12
# this is because wc only accepts standard input instead of argument list
$ wc
Hello World
1 2 12
# therefore, we do not need to use xargs