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 "$-" in *i*) echo This shell is interactive ;; *) echo This shell is not interactive ;; esac
Alternatively, startup scripts may examine the variable PS1; it is unset in non-interactive shells, and set in interactive shells. Thus:
if [ -z "$PS1" ]; then echo This shell is not interactive else echo This shell is interactive fi