It is often necessary for a network or system administrator to understand the network configuration of his/her network and computer systems. The 'nmap' command gives this capability. The command has many options. Type 'nmap' at a command prompt to get a “simple” summary of options. The man page contains over 2000 lines. Additional references are available at http://nmap.org. There is an entire book, Nmap Network Scanning, available for purchase. About half of its content is available here: http://nmap.org/book/toc.html.
As you can see, nmap is a very powerful and complicated command. You are to write a bash script, named scan.sh, that will help its user to invoke the nmap command with appropriate options. This can be accomplished by accepting options from the command line, presenting the user with a menu from which to choose options, retrieving options from a text file, or some combination of these or other methods.
Caution: Many system administrators resent network scans, as they are frequently a prelude to an attack. Thus, confine your scans to machines that you have obtained permission to scan from the person responsible for that machine. Failure to do so may result in an unexpected visit from the Network Police.