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

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
DifficultyEasy (rss)
Root privilegesNo
RequirementsGNU/Bash
Estimated completion timeN/A

Find out if this shell interactive using PS1

The syntax is as follows:

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

OR


[ -z "$PS1" ] && echo "This shell is not interactive" || echo "This shell is interactive"

OR


[ -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
 

From the bash 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:

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

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" ;;
 
References:
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{ 5 comments… add one }

  • Shantanu Gadgil November 6, 2012, 8:40 am

    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?

    • jonus June 25, 2013, 1:00 pm

      that will miss the action on a fresh login.

  • Jalal Hajigholamali November 27, 2012, 6:53 am

    Hi,

    Very useful article
    Thanks a lot..

  • Mike February 12, 2013, 4:36 pm

    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.

  • felipe1982 November 27, 2013, 12:09 am

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

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