Pipeline Redirection using the tee command in Linux

The tee command reads from standard input and write to standard output and files at the same time. It can copy standard input to each FILE, and to standard output. The tee command is useful when you want not only to send some data down a pipe, but also to save a copy. This tutorial is all about Pipeline Redirection using the tee command in Linux.

Analogy:  imagine data as water flowing through a pipeline, tee can be visualized as a “T” joint in the pipe which directs output in two directions.

Pipeline Examples of using the tee command

1. Pipeline Redirection using the tee command in Linux – Redirect the output of the ls command to file and pass it to less to be displayed on terminal

   ls -l | tee /home/technnix/saved-output | less

2.  Count number of characters in our file and also save the output to new text file

   # wc -l index.html| tee html_wc.txt
   308 index.html
   
   # cat html_wc.txt
   308 index.html
   
   

    

3.  List the last 10 changed files in the Linux file system and dave the output

   # ls -t | head -n 10 | tee /tmp/ten-last-changed-files.txt
   tmp
   root
   boot
   run
   etc
   dev
   sys
   proc
   srv
   var
   
   # cat /tmp/ten-last-changed-files.txt
   tmp
   root
   boot
   run
   etc
   dev
   sys
   proc
   srv
   var

    

4. Pipeline Redirection using the tee command in Linux – Check Disk usage using df -h and save the output to a file

   # df -h | tee disk_usage_file.txt
   Filesystem      Size  Used Avail Use% Mounted on
   devtmpfs        4.0M     0  4.0M   0% /dev
   tmpfs           865M     0  865M   0% /dev/shm
   tmpfs           346M  8.0M  339M   3% /run
   /dev/sda1        38G  2.8G   34G   8% /
   /dev/sda14       64M  7.0M   57M  11% /boot/efi
   tmpfs           173M     0  173M   0% /run/user/1000
   
   # cat disk_usage_file.txt
   Filesystem      Size  Used Avail Use% Mounted on
   devtmpfs        4.0M     0  4.0M   0% /dev
   tmpfs           865M     0  865M   0% /dev/shm
   tmpfs           346M  8.0M  339M   3% /run
   /dev/sda1        38G  2.8G   34G   8% /
   /dev/sda14       64M  7.0M   57M  11% /boot/efi
   tmpfs           173M     0  173M   0% /run/user/1000

    

Conclusion

The tee command is useful when you happen to be transferring a large amount of data and also want to summarize that data without reading it a second time e.g when downloading a huge file, we often want to verify its signature or checksum immediately.

# wget -O - https://example.com/dvd.iso | tee ubuntu2204.iso | sha1sum > ubuntu2204.sha1

The command above is efficient since it interleaves the download and SHA1 computation. We’ll get the checksum for free, because the entire process parallelizes so well.

See also:

1. How copy all the content of a file in Vim to clipboard