CT320 Bash Lab II                

Group Project                

You may work in pairs, if space demands.                 

Purpose                

The purpose of this assignment is to get more experience writing Linux scripts using bash and other commands. You will create and edit a bash script called pwval that uses many of the features of shell scripts described in the lecture.                 

Password file entry                

Lines in /etc/passwd looks like this:                 

    root:x:0:0:root:/root:/bin/bash
    applin:$1$ABCEc3XC$3GRtcuWtLxZ.4SinXGTey0:2464:1555:Jack Applin:/s/parsons/d/fac/applin:/bin/bash

The fields, separated by colons, are:                 

1. username (e.g., “jsmith42”)
2. encrypted password
3. numeric user ID
4. numeric group ID
5. user name (e.g., “John Smith”)
6. home directory
7. shell program

Program                

You will write a bash script called pwval that ensures that /etc/passwd is good. It will:                 

1. verify permissions on /etc/passwd
2. no duplicate usernames
3. no duplicate userids
4. for every entry, verify that:
   • the password is non-empty
   • the home directory exists
   • the shell exists and is executable
   • the group exists in /etc/group

Argument                

If an argument is given, then it is a file to be used instead of /etc/passwd. This is useful for testing.                 

Messages                

Think of this program as something to be executed every day, from cron. Therefore, it should be relatively quiet. It shouldn’t say anything, unless bad things are detected.                 

However, when the script does emit an error message, it must contain sufficient information to track down the problem. For example, an error message that simply says “duplicate user name” is insufficient—the message must specify, at least, what the duplicate user name is.                 

All error messages must include the name of the file (not always /etc/passwd) that is being processed. Also, error messages must include $0, so that it’s clear where the messages are coming from.                 

Temporary Files                

All temporary files should be in /tmp. Use $$ to ensure a unique file name. Don’t leave any temporary files around.                 

Get Credit                

When you have tested your script, and it works, show your work to the TA.