Question

I am writing a program that somewhat mimics the last command in UNIX, and I am trying to use backreferencing in my solution. My program does exactly what it is supposed to do but I get a run time error/warning. My question is why is this error/warning coming up and how can I fix an issue like this?

If you need more information I can provide.

Program Execution

./last dodoherty

OUTPUT

Here is a listing of the logins for dodoherty:

1. dodohert pts/1        pc-618-012.omhq. Wed Feb  8 09:19   still logged in
2. dodohert pts/6        ip98-168-203-118 Tue Feb  7 19:19 - 20:50  (01:31)
3. dodohert pts/3        137.48.207.178   Tue Feb  7 14:00 - 15:06  (01:05)
4. dodohert pts/1        137.48.219.250   Tue Feb  7 12:32 - 12:36  (00:04)
5. dodohert pts/21       137.48.207.237   Tue Feb  7 12:07 - 12:23  (00:16)
6. dodohert pts/11       ip98-168-203-118 Mon Feb  6 20:50 - 23:29  (02:39)
7. dodohert pts/9        ip98-168-203-118 Mon Feb  6 20:31 - 22:57  (02:26)
8. dodohert pts/5        pc-618-012.omhq. Fri Feb  3 10:24 - 10:30  (00:05)
Use of uninitialized value $1 in addition (+) at ./odoherty_last.pl line 43.
Use of uninitialized value $2 in addition (+) at ./odoherty_last.pl line 44.
Here is a summary of the time spent on the system for dodoherty:

dodoherty
8
8:6

The Code (Snippet of where the error is coming from, Also this is the only time $1 and $2 are used.)

foreach my $line2 (@user)
{
        $line2 =~ /\S*\((\d{2,2})\:(\d{2,2})\)\s*/;
        $hours = $hours + $1;
        $mins = $mins + $2;

        if( $mins >= 60 )
        {
                $hours = $hours + 1;
                $mins = $mins - 60;
        }
}

Answer 1

I think the problem might be in the following line.


1. dodohert pts/1 pc-618-012.omhq. Wed Feb 8 09:19 still logged in


That is because nothing matches the pattern so $1 and $2 are undefined.