manipulation of ps command output

wube has asked for the wisdom of the Perl Monks concerning the following question:

fellow monks,
I am trying to left justify and condense multiple spaces the output from the "ps" command. I just can't get left justification to work. Help. My code is posted below:

#!/usr/bin/perl
#
#  ps format
$PSfmt = "\"pid,ppid,pgid,user\"";

#  ps command
$PScmd = `ps -ef -o $PSfmt`;

#
# run the command, output into array
@PSarray = $PScmd ;

#
#  eliminate leading spaces, and condense spaces
for (@PSarray) {s/^\s+//;
                s/ +/ /g;
                print "$_ \n";
          }
exit;
[download]

I can do this with "sed" but I prefer to stick to using Perl.

for $rec (@PSarray)
    {
    $rec = `echo "$rec"|tr -s ' '|sed 's/^ //'`;
    print "$rec\n";
    }
exit;
[download]

I hope someone can show me how to do this in Perl.
Thanks in advance.

Comment on manipulation of ps command output Select or Download Code

Replies are listed 'Best First'.
Re: manipulation of ps command output by iguanodon (Priest) on Mar 09, 2004 at 23:20 UTC
Rather than parsing the output of ps, I like Proc::ProcessTable for this sort of thing.	[reply]
Re: manipulation of ps command output by borisz (Canon) on Mar 09, 2004 at 21:20 UTC
#!/usr/bin/perl # # ps format $PSfmt = "\"pid,ppid,pgid,user\""; # ps command $_ = `ps -ef -o $PSfmt`; # # eliminate leading spaces, and condense spaces s/^\s+//gm; s/ +/ /gm; print "$_ \n"; [download] Boris	[reply] [d/l]
Re: manipulation of ps command output by matija (Priest) on Mar 09, 2004 at 21:18 UTC
This is your problem line: `@PSarray = $PScmd ;` [download] By that point, `$PScmd` already contains the result of the command. You are assigning all the lines to `$PSarray[0]`. There are two ways to fix your code, that I can see: Split the result into lines: `@PSarray=split(/\n/,$PScmd);` Or do the substitution on the whole string, but change how the RE engine interprets it: `s/^\s+//m`. (The m modifier tells the regexp engine to make ^ and $ match start and end of line instead of start and end of string).	[reply] [d/l] [select]
Re: manipulation of ps command output by TilRMan (Friar) on Mar 10, 2004 at 04:57 UTC
While matija has your bugfix, you could try the line-by-line approach: `open PS, 'ps -ef -o pid,ppid,pgid,user \|' or die; while (<PS>) { tr/ //s; s/^ //; print; } close PS or die;` [download] but I think what you really want is `split` and `join` (or `$"` or `$,`). Some golfing gives: `#!/bin/sh ps -ef -o pid,ppid,pgid,user \| /usr/bin/perl -lape '$_="@F"'` [download] -- LP^>	[reply] [d/l] [select]
Re: manipulation of ps command output by Fletch (Bishop) on Mar 09, 2004 at 21:17 UTC
Erm, have you tried perl's `tr///`? `$_ = "a b c"; tr/ / /s; print;` [download]	[reply] [d/l] [select]
Re: manipulation of ps command output by captain_haddock (Novice) on Mar 11, 2004 at 13:55 UTC
If you are using a Un*x platform, you may want to look at Proc::ProcessTable. This is from the perldoc.... `# A cheap and sleazy version of ps use Proc::ProcessTable; $FORMAT = "%-6s %-10s %-8s %-24s %s\n"; $t = new Proc::ProcessTable; printf($FORMAT, "PID", "TTY", "STAT", "START", "COMMAND"); foreach $p ( @{$t->table} ){ printf($FORMAT, $p->pid, $p->ttydev, $p->state, scalar(localtime($p->start)), $p->cmndline); }` [download]	[reply] [d/l]
Re: manipulation of ps command output by zentara (Cardinal) on Mar 10, 2004 at 16:34 UTC
Some wise old monk, showed us this awhile back, a different approach. `#!/usr/bin/perl for (split '\n',qx(ps -u $> -o pid,ppid,pgid,user --no-headers)) { ($pid, $ppid, $pgid,$user) = unpack "a5 x a5 x a5 x a20",$_; print "$pid $ppid $pgid $user\n"; }` [download] I'm not really a human, but I play one on earth. flash japh	[reply] [d/l]