While using the command line, you can directly pass the output of one program (for example a tool that generates some system information or statistics) as input for another program (such as text-filtering or pattern searching tools like grep, sed or awk, for further processing), using a pipeline.
Two of the most important command-line utilities that can be used with pipelines to build command lines are:
- xargs – reads streams of data from standard input, then generates and executes command lines.
- tee – reads from standard input and writes simultaneously to standard output and one or many files. It’s more of a redirection command.
The simplest syntax for using a pipe, which you might have already seen in commands in many of out Linux tutorials, is as follows. But you can build a longer command line with several commands.
$ command1 args | command2 args OR # command1 args | command2 args | command3 args ...
Below is an example of using a pipeline to pass the output of dmesg command to head command.
$ dmesg | head
How to Use xargs to Run Commands
In this example, the second command converts multi-line output into a single line using xargs.
$ ls -1 *.sh $ ls -1 *.sh | xargs
To count the number of lines/words/characters in each file in a list, use the commands below.
$ ls *.sh | xargs wc -l #count number of lines in each file $ ls *.sh | xargs wc -w #count number of words in each file $ ls *.sh | xargs wc -c #count number of characters in each file $ ls *.sh | xargs wc #count lines, words and characters in each file
The command below finds and recursively deletes the directory named All in the current directory.
$ find . -name "All" -type d -print0 | xargs -0 /bin/rm -rf "{}"
The find command with option -print0 action enables printing of the full directory path on the standard output, followed by a null character and -0 xargs flag deals with space in filenames.
How to Use Tee with Commands in Linux
This example shows how to send command output to standard output and save to a file; the command below allows you to view top running processes by highest memory and CPU usage in Linux.
$ ps -eo cmd,pid,ppid,%mem,%cpu --sort=-%mem | head | tee topprocs.txt $ cat topprocs.txt
To append data in an existing file(s), pass the -a flag.
$ ps -eo cmd,pid,ppid,%mem,%cpu --sort=-%mem | head | tee -a topprocs.txt
You can find more information in tee and xargs man pages.
$ man xargs $ man tee
