http://qs321.pair.com?node_id=82697

This could be a bother to write in any other language, but Perl makes it so easy that it would be silly not to build it. It is a simple tool.
It does only this: Grab the web page containing the load stats on the login machines at my university. Select the server with lowest load and launch ssh.
I for one feel taht this is the biggest use for Perl. Those small nice hacks that just make life a bit... smoother. Imagine how long this little widget would be written in any other language.

#!/usr/bin/perl -w
if ( $#ARGV != 0 ) {
 print "efd v1.0 by d99msr\n";
 print "Usage:\n";
 print "        efd username\n";
 exit;
}
my $user = $ARGV[0];
use HTTP::Request::Common;
use LWP::UserAgent;
print "Retrieving and parsing load average stats.\n";
my $ua = LWP::UserAgent->new;
my $req = GET 'http://www.efd.lth.se/loginload.shtml';
my @raw = split("\n", $ua->request($req)->as_string);
my $lowest = 10;
my $machine;
foreach (@raw) {
 if ( $_ =~ m/TR.*TD.*TD.*TD.*TD.*TD.*TD.*TD.*TD.*TD.*TD.*TD.*TD.*TR/)
+ {
  $_ =~ s/\<.*?\>\<.*?\>/\<\>/ig;
  $_ =~ s/ //g;
  @split = split("<>", $_);
  if ( $split[5] < $lowest ) {
   $lowest = $split[5];
   $machine = $split[1];
  }
 }
}
print "Connecting to $machine, load average: $lowest\n";
my $efdname = "$user\@$machine.efd.lth.se";
exec("ssh $efdname");
exit;

[download]


Odie

--
I am a manual signature virus. Copy me please!

Replies are listed 'Best First'.
Re: Nothing special. Isn't that what Perls all about?
by merlyn (Sage) on May 24, 2001 at 00:28 UTC
    Or, more succinctly: 
    #!/usr/bin/perl

use LWP::Simple;
use HTML::TableExtract;

my $html = get "http://www.efd.lth.se/loginload.shtml"
  or die "Cannot get!\n";

my $te = HTML::TableExtract->new(headers => ['Name', 'Load average']);
$te->parse($html)->eof;
my @sorted = sort { $a->[1] <=> $b->[1] or $a->[0] cmp $b->[0] } $te->
+rows;

for (@sorted) {
  print "$_->[0] has load of $_->[1]\n";
}

print "exec ssh $sorted[0][0]\n";

    [download]

    -- Randal L. Schwartz, Perl hacker

[reply]
[d/l]
[reply]
Re: Nothing special. Isn't that what Perls all about?
by btrott (Parson) on May 24, 2001 at 00:45 UTC
    I'm no regex whiz, but I think you're making Perl do a lot of extra work with that regex to match table rows. All of those dot-stars means a lot of backtracking, I think.

    Anyway, here's a slightly modified version: 

        use LWP::Simple;
    my $user = shift or die "usage: $0 <username>";

    $_ = get "http://www.efd.lth.se/loginload.shtml"
        or die "Cannot get!\n";

    my $re = '<TR ALIGN=center>' . ('<TD>\s*([^<]+)</TD>' x 6) . '</TR
+>';

    my($load, $host);
    while (/$re/g) {
        $host = $1, $load = $5 if !defined $load || $5 < $load;
    }

    print "Host $host has load of $load\n";
    exec("ssh $user\@$host.efd.lth.se")
        or die "Can't exec ssh: $!";

    [download]
    Note also that I took out the exit after the exec--you don't need that, because exec never returns.

    I think my regex might be a little more friendly, but I'm not absolutely sure. Note also that any regex solution will be less robust and less succeptible to HTML formatting changes than a solution like merlyn's.

    Updated to test return value from exec, because I should've been more clear about exec and the possibility that it could return.

[reply]
[d/l]
      exec returns if the program to be execed is not there.
[reply]
Re: Nothing special. Isn't that what Perls all about?
by weingart (Acolyte) on May 24, 2001 at 23:20 UTC
    Perl is good, Perl is great, why not just Unix we appreciate? 
    ssh `lynx -dump http://www.efd.lth.se/loginload.shtml | grep Ul | tr -
+s ' ' | cut -d' ' -f2,8 | sort -n -k 2 | head -1 | cut -d' ' -f1`

    [download]
[reply]
[d/l]

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