$ cat stack.sh
#!/bin/sh
if [[ $1 = "-o" ]]; then
echo "Option -o turned on"
else
echo "You did not use option -o"
fi
$ bash stack.sh -o
Option -o turned on
$ bash stack.sh
You did not use option -o
FYI:
$1 = First positional parameter
$2 = Second positional parameter
.. = ..
$n = n th positional parameter
For more neat/flexible options, read this other thread: Using getopts to process long and short command line options