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From: ted@evi.com (Ted Stefanik)
Newsgroups: comp.lang.perl
Subject: Scanning "ps" output with Perl
Message-ID: <1991May3.162019.5613@uvaarpa.Virginia.EDU>
Date: 3 May 91 16:20:19 GMT
Sender: mmdf@uvaarpa.Virginia.EDU (Uvaarpa Mail System)
Reply-To: ted@evi.com (Ted Stefanik)
Organization: The Internet
Lines: 38

I've noticed that several Perl utilities scan "ps" output using splits
and/or regular expressions.  I'd like to add some cautions to these
approaches.

When a particular process's statistics numbers get too big for the column space
alloted to that number, ps just slams the number into the preceeding column.

For example, this looks nice:

USER       PID %CPU %MEM   SZ  RSS TT STAT  TIME COMMAND
ted      18374 51.2  3.0  488  380 p0 R     0:00 ps auxww

If the process got memory hoggy and CPU hoggy, and was niced and not currently
active, you'd get:

USER       PID %CPU %MEM   SZ  RSS TT STAT  TIME COMMAND
ted      18374 51.2  3.012488 1380 p0 IWN2345:45 ps auxww

Notice that the size and time fields blend into the previous fields.

In my opinion, splitting is out.  You have to be very careful with regular
expressions, because the white space is not always gauranteed to be there.  I
use substr, but that would also fail if the fields overflow one more place:

USER       PID %CPU %MEM   SZ  RSS TT STAT  TIME COMMAND
ted      18374 51.2  3.0124888 1380 p0 IWN12345:45 ps auxww

(Although I both these are unlikely on my machine - 65MB swap space with
weekly reboots.)


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