check isatty in bash

You could make use of the /usr/bin/tty program:

if tty -s
then
    # ...
fi

I admit that I'm not sure how portable it is, but it's at least part of GNU coreutils.

to elaborate, I would try

 if [ -t 0 ] ; then
    # this shell has a std-input, so we're not in batch mode 
   .....
 else
    # we're in batch mode

    ....
 fi

I hope this helps.

Note that in bash scripts (see the test expr entry in man bash), it is not necessary to use the beefy && and || shell operators to combine two separate runs of the [ command, because the [ command has its own built-in and -a and or -o operators that let you compose several simpler tests into a single outcome.

So, here is how you can implement the test that you asked for — where you flip into batch mode if either the input or the output has been redirected away from the TTY — using a single invocation of [:

if [ -t 0 -a -t 1 ]
then
    echo Interactive mode
else
    echo Batch mode
fi

From help test:

 -t FD          True if FD is opened on a terminal.