Fork two extra processes (or maybe just one) -- one to run the application, and the other to monitor the directory contents. 
if ($proc_pid = fork) {
  # parent
}
elsif (defined $proc_pid) {
  exec $command, @args;
  die "can't exec $command @args: $!";
}
else {
  die "can't fork: $!";
}

if ($count_pid = fork) {
  # parent
}
elsif (defined $count_pid) {
  opendir DIR, $dir_to_be_watched
    or die "can't open $dir_to_be_watched: $!";
  while (1) {
    # UPDATED -- who cares WHAT the files are?
    my $files = -2;  # -2 for . and ..
    $files++ while defined readdir DIR;
    last if $files == $N;
    rewinddir DIR;
  }
  kill -TERM => $proc_pid;
  exit;
}
else {
  die "can't fork: $!";
}

# parent can go on its merry way

[download]


japhy -- Perl and Regex Hacker

In reply to Re: Running external program until N files created by japhy
in thread Running external program until N files created by Tuna

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