Question

I’m creating a script to detect which user didn’t connect to the server for a while.

So far everything is good but now trying to remove some unwanted entry from the list produced from my script. I would like to add an exception to my script so that when lastlog is called with a non used argument, the ouput isn’t printed to the screen.

I’ve tried somthing like :

if [ $? -gt 0 ]; then
    echo "ERROR!"
fi

But the problem is that lastog is returning 0 on success but simply :

lastlog: Unknown user or range: infolog

on error. So I cannot catch the exeption.

Here’s my code (which is pretty simple)

#!/bin/bash
FILES=../*

for year in 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
do
    for f in $FILES
    do
        tempUser=${f:3:20}
        userCommand=`lastlog -u $tempUser | grep $year`

        if [ ${#userCommand} != 0 ]   
        then
          echo "$userCommand"
        fi

    done
done

Answer 1

You can test this pretty simply, but on my handy linux box lastlog does indeed set a nonzero status for a bad user name:

$ if lastlog -u nosuchuser; then echo no error; else echo error; fi
lastlog: Unknown user or range: nosuchuser
error

If you’re running this in a pipe, the problem is that the “status” of a pipe sequence is the status of the last element of the pipeline:

$ progA | progB | progC
$ echo $?

prints the status for progC.

If you use bash, you can get the status from everything via bash’s PIPESTATUS array variable:

bash$ progA | progB | wc
bash: progB: command not found
bash: progA: command not found
      0       0       0
bash$ echo ${PIPESTATUS[@]}
127 127 0
bash$

which should get you the rest of the way there.

---

Edit: you might not even care, and just be looking for a way to throw away stderr output from lastlog, in which case, consider:

$ lastlog 2>/dev/null | grep ...