script with simple flag
===

Suppose I have this simple script

    #! /bin/sh
    
    if [ $# -ne 2 ]
    then
            echo "Usage: $0 arg1 arg2"
            exit 1
    fi
    
    head $1 $2

    ## But this is supposed to be:
    ## if -f flag is set, 
    ##      call [tail $1 $2]
    ## else if the flag is not set
    ##      call [head $1 $2]


So what's the simplest way to add a 'flag' checking to my script?

Thanks
