Emulating UNIX 'top' on AIX

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

AIX doesn't have a 'top' command. Well, I'd like to create an emulation for it using perl and "ps guw" piped to sort. I have the following so far:

...
my $pid = fork(); # spawn child

if ( $pid ) { # parent
  while ( wait != -1 ) {
    while (<>) {
      print "Got $_ on STDIN\n";
    }
  }
} else {  # child
  while ( 1 ) {
    print $header;
    print `ps guw | sort -n -r -k $sort_option | head -$num_lines`;
    print "\nSort: $sort_option : Lines: $num_lines : Sleep: $sleep_ti
+me\n";
    sleep $sleep_time;
    print `clear`;
  }
}
[download]

Pretty rudimentary, but what I would like to do is have the parent process listen for STDIN, like top does, and send a SIGHUP to the child to reset it's sort options, lines or whatnot. The while (<>) { doesn't seem to be working like I'd hoped. Any ideas on this one?

Comment on Emulating UNIX 'top' on AIX Select or Download Code

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Re: Emulating UNIX 'top' on AIX by jfroebe (Parson) on May 02, 2005 at 15:52 UTC
Hi, Why not install the GNU version of top? http://directory.fsf.org/procps.html Jason L. Froebe Team Sybase member No one has seen what you have seen, and until that happens, we're all going to think that you're nuts. - Jack O'Neil, Stargate SG-1	[reply]
Re^2: Emulating UNIX 'top' on AIX by Transient (Hermit) on May 02, 2005 at 15:53 UTC
This isn't an option due to access restrictions. As I said previously, I also would like to do this simply for proof of concept :)	[reply]
Re: Emulating UNIX 'top' on AIX by ajt (Prior) on May 02, 2005 at 16:23 UTC
If you get anywhere you should submit it to PPT: Unix Reconstruction Project. I had a quick peek, and they don't have top done, so anything you get to work will be accepted I'm sure. Good Luck. -- ajt	[reply]
Re: Emulating UNIX 'top' on AIX by tcf03 (Deacon) on May 02, 2005 at 15:15 UTC
What about topas? Ted -- "Men have become the tools of their tools." --Henry David Thoreau	[reply]
Re^2: Emulating UNIX 'top' on AIX by Transient (Hermit) on May 02, 2005 at 15:17 UTC
Doesn't seem to work on my system, for some reason. :-S Besides - it's a fun little utility and I've got nothing better to do :)	[reply]
Re: Emulating UNIX 'top' on AIX by ikegami (Patriarch) on May 02, 2005 at 15:40 UTC
Is the problem that `<>` blocks? Try Term::ReadKey By the way, `<>` does not necessarily read from `STDIN`. `<STDIN>` does.	[reply] [d/l] [select]
Re^2: Emulating UNIX 'top' on AIX by Transient (Hermit) on May 02, 2005 at 15:59 UTC
Well, I got around the blocking issue. I used `waitpid $pid, WNOHANG` and I can now read in from STDIN. The next issue is to read character by character instead of line by line. Is there any pure Perl way to do this?	[reply] [d/l]
Re^3: Emulating UNIX 'top' on AIX by Transient (Hermit) on May 02, 2005 at 16:09 UTC
Ok, found some stuff about getc from the docs... using that seems to work! I'll post the code at the end for critique and future use.	[reply]
Re^3: Emulating UNIX 'top' on AIX by ikegami (Patriarch) on May 02, 2005 at 16:12 UTC
No. `<FILE>`, `getc`, `read` and `sysread` all block until a newline is read (even if they only return one character at a time). That's why I mentioned Term::ReadKey. Well, maybe you can do something with PerlIO. I don't know anything about that.	[reply] [d/l] [select]
Re^4: Emulating UNIX 'top' on AIX by Transient (Hermit) on May 02, 2005 at 16:18 UTC
Re: Emulating UNIX 'top' on AIX by Transient (Hermit) on May 02, 2005 at 16:57 UTC
Ok. So now I am able to fork, process the system calls and read characters using the parent. My next problem is how to communicate an option change to the child. I was originally considering SIGHUP, but I had forgotten that it is primarily used where information is stored in a file. I could fork for each sleep cycle, but that seems wasteful. Or I could explicitly kill the child and respawn a new one with new options. Which, for some reason, seems like cheating. Another option would be to use only a single process and determine a way to make any input to be a signal interrupt which would need to be processed (and I'm not sure this would work). Any other ideas out there?	[reply]
Re^2: Emulating UNIX 'top' on AIX by 5mi11er (Deacon) on May 02, 2005 at 21:22 UTC
You could setup a communication pipe between the two processes and use a non-blocking select to determine if information is there to be read... or use SIGHUP, regardless of what anyone thinks it's reserved for... do the kill/respawn thing, but I think that's going to be widely regarded as an ugly option I think a fork per sleep cycle is even worse than the above option. Do the single process thing, with a non-blocking select to determine if there is input to read Personally, I believe the first or last options are the better options... -Scott	[reply]