Hi I'm looking to pipe a few commands to generate a userlist from /etc/passwd. I want to get only users with valid shells and exclude system accounts. I would check UID's but there are superusers in the same range as the system accounts. Here's what I have so far. Any suggestions on how I can use awk in a grep command?

cat passwd | grep -e "/bin/bash" | awk 'BEGIN { FS=":" } { print $1 }' | grep -v "awk '{ print $1 }' /etc/services"


This doesn't quite work because mysql is still in the list. What am I doing wrong?

All that piping is really unecessary. awk alone can do what (what I think) you want.

awk -F: '{ if ( $6 == "/bin/bash" ) print $1 }'

ps: this assumes your definition of "valid shell" is just limited to /bin/bash.

pps: system accounts are usually created below a certain UID value. something is probably wrong on your box if system accounts are interleaved with user accounts.

Hi,

This is not as easy as it looks. As you already noticed, there are system accounts with a login shell.
Your original idea, using the UID, could be used. It will fail also if system users (with a /bin/bash shell) are added after normal users.

Root always has uid 0 and normal users have a uid range starting a lot higher (some it is 100 and up, some 500). All other (system) users are between 1 and say 99 (100 being the first uid used for a normal user).

Something like this would work in this situation:

awk 'BEGIN { FS=":" } $3 == 0 || $3 > 99 { print $1 }' /etc/passwd

This checks to see if field 3 (uid field in passwd) is 0 (zero) or larger then 99 if so it will print field one (user).

You could even include a check for a valid shell:

awk 'BEGIN { FS=":" } ( $3 == 0 || $3 > 99 ) && ( $7 == "/bin/bash" ) { print $1 }' /etc/passwd

Field 7 (shell) must also be /bin/bash. The rest of the command is the same.

PS: If a user is added (normal or otherwise) the uid is increased by one, so if you add a system user after the normal users are added (and don't include a low uid) the above command will fail if the system user has a valid bash shell.

Hope this clears things up.

Thanks for your reply ugenn, nice solution. Unfortunately I need to use pipes for this class right now. I guess the box is pretty messy. Some of the system accounts have shells but I don't want to include them. Do you know how I would incorporate awk into the grep expression?

I have a few others I want to try like making a MTA alias for the userlist I made:

cat passwd | grep -e "/bin/bash" | awk 'BEGIN { FS=":" } { print $5 " <"$1"@cs.sierracollege.edu>" }'

but some of the users have their phone numbers in the name column like

Jason Linder,CS 50,(916)777-7777,(916)555-5555 <un269@cs.sierracollege.edu>

How could I get only the name first and last using one long piped expression?

Hi again,

The pipe might not be long enough, but here we go:

cat passwd | grep "/bin/bash" | awk -F: '$5 ~ /cs.sierracollege.edu/ { print $1 }'

The above checks to see if the string cs.sierracollege.edu is present anywhere in field 5. If so it prints field one.

Hope this helps.