First off, this is my first posting on perlmonks and my first real perl script, so pls be gentle...

The script below is used to run multiple instances of the required command (ping, ssh, any function as reqd, but also uses sleep for testing) in a sub. To launch and manage/limit the instances running at any 1 time, I use fork and waitpid.

The input file is a plain text file containing hostnames. In the full script, the hostname is passed to the sub in question, but as this is not required for testing with sleep I have taken it out.

When I run the script with "for (<IN>)" the script works fine, but this will create a temp array (so I'm told). As the input file/list of hosts will run into the 1000's this will use memory where ideally it shouldnt. If I use "while (<IN>)" (which does not create a temp array/use memory), the script just loops the inputfile. It will run until you kill it, regardless of how many hosts are in the input file.

I'd like to do this cleanly with "while" rather than "for" if possible. Does anyone have any good/clean/noob friendly ideas? It may be easier to bite the bullet & use "for", but I thought I'd ask first...

perl version is 5.8.5

Regards
Paul

## Additional Info ##
Apologies for not including in original post:

The loop only occurs when the "waitpid" function is called. If the max number of runs is not met ($max=2 in example), the while finishes ok.

As such this may be a while/fork or waitpid issue.

#!perl -w

use strict;
use Data::Dumper;

my $prog=$0;
my ($estat,$infile,$errfile,$action,$sub,$thishost,$pid,$cpid,$pidstat
+,$thiskey);
my (%track,%closed);

my $max=2;
my $rcount=0;
my $tcount=0;

$infile=$ARGV[0];
open(IN,'<',$infile) || die "cannot open input file $infile \"$!\"";

sub _sleep {
 sleep int(rand(10));
 return $?>>8;
}

sub _waitpid {
 my $cpid=waitpid(-1,0);
 my $pidstat=$? >> 8;
 $closed{$track{$cpid}}=$pidstat;
 $rcount--;
}

#here
while (<IN>) {
#for (<IN>) {
 chomp;

 $rcount++;
 $tcount++;
 print "Progress: $tcount\r";
 $pid = fork;

 if ($pid==0) {
 # child
  close IN;
  # start call sleep sub
  my $estat=_sleep;
  exit $estat;
  # end call sleep sub

  # start direct sleep
  #sleep int(rand(10));
  #exit $?>>8;
  # end direct sleep
 }
 else {
 # parent
  $track{$pid}=$_;
  if ( $rcount >= $max ) {
   # start call waitpid sub
   _waitpid();
   # end call waitpid sub
   # start direct waitpid
   #my $cpid=waitpid(-1,0);
   #my $pidstat=$? >> 8;
   #$closed{$track{$cpid}}=$pidstat;
   #$rcount--;
   # end direct waitpid
  }
  else {
  }
 }
}

print "\n\nWaiting for procs to finish...\n";
while ($rcount>0) {
 _waitpid();
}
print "Done\n";

for $thiskey (keys %closed) {
 print "$thiskey $closed{$thiskey}\n";
}
print Dumper(\%closed);

close IN;
print "End\n";
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