交互式shell和非交互式shell

6.3.1 What is an Interactive Shell?

An interactive shell is one started without non-option arguments, unless -s is specified, without specifying the -c option, and whose input and error output are both connected to terminals (as determined by isatty(3)), or one started with the -i option.

An interactive shell generally reads from and writes to a user’s terminal.

The -s invocation option may be used to set the positional parameters when an interactive shell is started.

6.3.2 Is this Shell Interactive?

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:

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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:

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if [ -z "$PS1" ]; then
        echo This shell is not interactive
else
        echo This shell is interactive
fi