6.3.2 Is this Shell Interactive?
To determine within a startup script whether or not Bash is
test the value of the '-' special parameter.
i when the shell is interactive. For example:
case "$-" in
*i*) echo This shell is interactive ;;
*) echo This shell is not interactive ;;
Alternatively, startup scripts may examine the variable
PS1; it is unset in non-interactive shells, and set in
interactive shells. Thus:
if [ -z "$PS1" ]; then
echo This shell is not interactive
echo This shell is interactive