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

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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.

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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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Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.

6 comment

  1. 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?

  3. 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.

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

    Is it just a matter of:

    useradd -s /sbin/nologin lisa

    Thanks

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