Shell Programming and Scripting

Hi all,

I've been trying to find a good check I can put it in to a shell script to see if a given user exists.

Some of the things I've thought about is checking whether they have a home directory, but not all users have a home directory. I've thought about grepping the /etc/passwd file for the username but if the username is short and happens to be a repeated string somewhere else in the file then this check could fail or be inaccurate too.

Ideally I would like a simple command so I can just use it in an if/else statement, so if the user exists then do this and if the user doesn't exist then do something else.

In case it helps it would be using the bash shell and would need to be supported by RedHat 9 and SuSE 10 but that shouldn't make too much difference.

Any ideas would be appreciated no matter how bizzare they may seem

Thanks.

You're close to a solution. Just improve your search string enough and you can fix the substring problem:

Code:

grep "^${USERNAME}:" /etc/passwd

The ^ means "from the beginning of the line", and the : is the field-delimiting character in /etc/passwd, so you're guaranteed to match either the entire username field or nothing at all.

there are lots of ways on checking if aa user exist besides the passwd file. you can use the "id" or the "finger" command which are reliable commands.

hope this helps.

many thanks

I wouldn't call finger reliable, being considered an obsolete security hole which most systems no longer bother to install by default. id, on the other hand, is a useful looking thing which I didn't know about. Thanks!

Nice one, totally forgot about the id command.

What's more embarassing is 10 lines up in the code I had the $(id -u) command to check the user was root!