Bash Check If Shell Is Interactive or Not Under Linux / Unix Oses

Author: Vivek Gite Last updated: May 5, 2020 6 comments

How do I check in GNU/Bash if a shell is running in interactive mode or not while writing shell scripts?

A bash shell is considered as an interactive shell when it reads and writes data from a user’s terminal. Most startup scripts examine the shell variable called PS1. Usually, PS1 is set in interactive shells, and it is unset in non-interactive shells.

Tutorial details
Difficulty level	Easy
Root privileges	No
Requirements	GNU/Bash
Est. reading time	N/A

Find out if this shell interactive using PS1

The syntax is as follows:

// Is this Shell Interactive?
[ -z "$PS1" ] && echo "Noop" || echo "Yes"

Here is another shortcut for us:

[ -z "$PS1" ] && echo "This shell is not interactive" || echo "This shell is interactive"
## do some stuff or die ##
[ -z "$PS1" ] && die "This script is not designed to run from $SHELL" 1 ||  do_interacive_shell_stuff

You can use bash shell if..else..fi syntax as follows:

if [ -z "$PS1" ]; then
       die "This script is not designed to run from $SHELL" 1
else
       //call our function
       do_interacive_shell_stuff
fi

Bash Check If Shell Is Interactive or Not on Linux and Unix

Is this shell interactive?

From the bash(1) reference manual:

To determine within a startup script whether or not Bash is running interactively, test the value of the ‘-‘ special parameter. It contains i when the shell is interactive. For example:

So we can use the case..in..esac (bash case statement)

 case "$-" in
 *i*)	echo This shell is interactive ;;
 *)	echo This shell is not interactive ;;
esac

OR we can use the if command:

if [[ $- == *i* ]]
then
    echo "I will do interactive stuff here."
else 
    echo "I will do non-interactive stuff here or simply exit with an error."
fi

Check in bash if a shell is running in interactive mode using the tty command

You can also use tty command as follows:

tty -s && echo "This shell is interactive" || echo "This shell is not interactive" ;;
##OR ##
ssh user@server1.cyberciti.biz tty -s && echo "This shell is interactive" || echo "This shell is not interactive" ;;

Use the test command

As per the comment, we can use the test command too:
-t FD file descriptor FD is opened on a terminal
Hence, we can use the following code snippet:

 if [ -t 0 ] ; then
    echo "Doing interactive stuff here in my bash script ..."
 else
    echo "Error ..."
 fi

Conclusion

You leaned how to check in GNU/bash if a shell is running in interactive mode or not using various command line options. See GNU/bash man page by typing the following bash command or by visiting this url:
man bash

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🐧 6 comments so far... add one ↓

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6 comments… add one

Shantanu Gadgil Nov 6, 2012 @ 8:40

Whatever happened to the standard method of checking the fd ‘0’ ???

if [ -t 0 ]; then
# do stuff
fi

Don’t you think that’s a better check that some env variable?

Reply Link
- jonus Jun 25, 2013 @ 13:00
  
  that will miss the action on a fresh login.
  
  Reply Link
Jalal Hajigholamali Nov 27, 2012 @ 6:53

Hi,

Very useful article
Thanks a lot..

Reply Link
Mike Feb 12, 2013 @ 16:36

Full of holes and not reliable at all. PS1 can be defined by someone in their own .bashrc file for instance.
You’d have to stat what /dev/fd/0 points to, and sift out the text that is different.

Reply Link
felipe1982 Nov 27, 2013 @ 0:09

@ Mike – what other solution do you propose, if -t 0 isn’t enought, nor is [ -z “$PS1” ]

Reply Link
Rey Mar 16, 2016 @ 10:27

Hi,
How can I create a user with non-interactive shell?

Is it just a matter of:

useradd -s /sbin/nologin lisa

Thanks

Reply Link