Shell script to scrape /etc/passwd data?

This is a surprisingly easy scripting task, actually, but there are some nuances worth mentioning: if you just blindly go through the /etc/passwd file, where all accounts are saved, you'll end up with lots of addresses like "postmaster" and "admin" and "ftp" and "uucp" and so on. Probably not what you want.

So the first step isn't just to pull out the account names, but to have some sort of rule-based extraction where you, for example, don't grab anything with a UserID of less than 100. This can be most easily done with the awk command, a highly scriptable and flexible pattern matching utility. Here's how I'd do this first step:

This will pull out all the account names where the ID is greater than 99, which should accomplish the first step of your task. The "-F:" tells awk to use colons as the field separators, then "$1" is the first field (account name) and "$3" is the account ID.

Now you have a stream of account names, guaranteed not to have spaces, so this can easily be produced in a subshell and then fed into a looping structure, thusly:

This four line Bourne shell script will do exactly what you seek. Change "hostname.com" to be the desired domain name, and run this script on your Linux or Unix box, and the output will be a stream of email addresses as per your specification.

I hope this helps you out! Also, I have a lot more about shell script programming in my acclaimed book Wicked Cool Shell Scripts, if this whets your appetite!