ow 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.

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

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

#ps1 #shell interactive #bash #syntax