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Linux tee command with examples

Introduction

The tee command reads standard input (stdin) and writes the result to standard output (stdout) and one or more files simultaneously.

It basically displays the command output on the terminal and at the same time redirects the output to a file. I often used tee command to append a new line to the root user files.

We’ll show how to use the tee command on Linux.

The basic syntax for the tee command is:

[command] | tee [options] [filename]

Usage of tee command

One of the basic uses of the tee command is to display the standard output (stdout) of a command and save it in a file. For instance, we have executed the ‘hostnamectl’ command to print our system’s hostname and other details, then save the standard output to ‘unixcop.txt’.

[root@unixcop ~]# hostnamectl | tee unixcop.txt
   Static hostname: unixcop
         Icon name: computer-vm
           Chassis: vm
        Machine ID: 7c8b674cab8340828e333aac68fa4a51
           Boot ID: ed756f0df66d4ed7aef6890f68b1e672
    Virtualization: kvm
  Operating System: CentOS Linux 8
       CPE OS Name: cpe:/o:centos:centos:8
            Kernel: Linux 4.18.0-305.10.2.el8_4.x86_64
      Architecture: x86-64
[root@unixcop ~]# 

The content of the ‘unixcop.txt’ file can be viewed using the cat command as follows:

[root@unixcop ~]# cat unixcop.txt 
   Static hostname: unixcop
         Icon name: computer-vm
           Chassis: vm
        Machine ID: 7c8b674cab8340828e333aac68fa4a51
           Boot ID: ed756f0df66d4ed7aef6890f68b1e672
    Virtualization: kvm
  Operating System: CentOS Linux 8
       CPE OS Name: cpe:/o:centos:centos:8
            Kernel: Linux 4.18.0-305.10.2.el8_4.x86_64
      Architecture: x86-64
[root@unixcop ~]# 

Write output to multiple files

This can also write output to multiple files. To do so, add a list of files separated by space as arguments.

# command | tee file1 file2…fileN

For example:

[root@unixcop ~]# cal | tee file1 file2 file3
     August 2021    
Su Mo Tu We Th Fr Sa
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31            
                    
[root@unixcop ~]# ls
anaconda-ks.cfg  file1  file2  file3  unixcop.txt
[root@unixcop ~]# 
[root@unixcop ~]# cat file1 file2 file3
     August 2021    
Su Mo Tu We Th Fr Sa
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31            
                    
     August 2021    
Su Mo Tu We Th Fr Sa
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31            
                    
     August 2021    
Su Mo Tu We Th Fr Sa
 1  2  3  4  5  6  7
 8  9 10 11 12 13 14
15 16 17 18 19 20 21
22 23 24 25 26 27 28
29 30 31            
                    
[root@unixcop ~]# 

Append output to a file

By default, the tee command overwrites the contents of a file, each time you run it. To append output, use the ‘-a or –append’ option.

# command | tee -a file

Ignore Interrupts

This option allows tee command to exit gracefully when the command has been interrupted with (CTRL+C) during execution. To do so, use the ‘-i or –ignore-interrupts’ option

# command | tee -i file

Hide the output

If you don’t want to print the command result to a standard output, use the following format:

# command | tee file >/dev/null

Use of tee command in shell script

The tee command can often be used in shell scripts to redirect the output to a file as shown below:

# vi /tmp/testbash.sh

#!/bin/bash
LOGFILE=/tmp/test-logs-$(date +%d%m%Y)
echo "Append the logs " | tee -a $LOGFILE

Tee help Option

It gives the help message and exit.
SYNTAX :

# tee --help
[root@unixcop ~]# tee --help
Usage: tee [OPTION]... [FILE]...
Copy standard input to each FILE, and also to standard output.

  -a, --append              append to the given FILEs, do not overwrite
  -i, --ignore-interrupts   ignore interrupt signals
  -p                        diagnose errors writing to non pipes
      --output-error[=MODE]   set behavior on write error.  See MODE below
      --help     display this help and exit
      --version  output version information and exit

MODE determines behavior with write errors on the outputs:
  'warn'         diagnose errors writing to any output
  'warn-nopipe'  diagnose errors writing to any output not a pipe
  'exit'         exit on error writing to any output
  'exit-nopipe'  exit on error writing to any output not a pipe
The default MODE for the -p option is 'warn-nopipe'.
The default operation when --output-error is not specified, is to
exit immediately on error writing to a pipe, and diagnose errors
writing to non pipe outputs.

GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Report tee translation bugs to <https://translationproject.org/team/>
Full documentation at: <https://www.gnu.org/software/coreutils/tee>
or available locally via: info '(coreutils) tee invocation'
[root@unixcop ~]# 

Conclusion

In this guide, we’ve shown you how to use tee command in Linux.

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