It's difficult to say without seeing the shell script you're running, but may I guess that it uses relative paths to binaries that should be in $PATH normally? Without the right values in that environment variable, the shell will not be able to find the commands.

To simplify the issue, I have removed the shell script and replaced it with a sleep command, which would be my long process. Below is the updated code that executes a 'sleep' command.

0 $ENV{PATH} = "/bin:";
1 use CGI qw(:all delete_all escapeHTML);
2 
3 my $redirect_page = "display_page.cgi";
4
5 # The execution enters this loop in the first pass whereas 6 it shou
+ld not!!!
7 if (my $session = param('session')) { # returning to pick 8 up sessi
+on data
9  my $cache = get_cache_handle();
10  my $data = $cache->get($session);
11  unless ($data and ref $data eq "ARRAY") { # something is wrong
12    show_form();
13    exit 0;
14  }
15  print header;
16  if ( $data->[0] ){
17  print start_html(-title=>'Sleep Results Done',-bgcolor=>'white');
18  # Checking.... print $session and $data->[0] to screen
20  print h2("$session");
21     print h2("$data->[0]");
22  # End of checking
23  print start_form(-name=>'data',-action=>$redirect_page);
24  print end_form();
25  print script("setTimeout(\"document.data.submit();\",2000);");
26  }
27  else{
28  print start_html(-title => "Sleep Results",
29                   ($data->[0] ? () :
30                    (-head => ["<meta http-equiv=refresh content=5>"
+])));
31  print h1("Sleep Results");
32  print pre(escapeHTML($data->[0]));
33  print pre(escapeHTML($data->[1]));
34  print p(i("... continuing ...")) unless $data->[0];  
35  
36  }
37  print end_html;
38 } 
39 elsif ( (my $slp = param('sleep')) eq 'sleep') {
40     my $session = get_session_id();
41    my $cache = get_cache_handle();
42    $cache->set($session, [0, ""]); # no data yet
43
44    if (my $pid = fork) {       # parent does
45      delete_all();             # clear parameters
46      param('session', $session);
47      print redirect(self_url());
48    } 
49    elsif (defined $pid) {    # child does
50      close STDOUT;             # so parent can go on
51      unless (open F, "-|") {
52        open STDERR, ">&=1";
53        exec "sleep","120";
54        die "Cannot execute Sleep: $!";
55      }
56      my $buf = "";
57      while (<F>) {
58        $buf .= $_;
59        $cache->set($session, [0, $buf]);
60      }
61      $cache->set($session, [1, $buf]);
62      exit 0;
63    } 
64    else {
65      die "Cannot fork: $!";
66    }
67 }
68 else {                        # display form
69  show_form();
70 }
71
72 exit 0;

sub show_form {
  print header, start_html("Sleep"), h1("Sleep");
  print start_form;
  #print submit('traceroute to this host:'), " ", textfield('host');
  print submit('Run Sleep Process:'), " ", textfield('sleep');
  print end_form, end_html;
}

sub get_cache_handle {
  require Cache::FileCache;

  Cache::FileCache->new
      ({
        namespace => 'sleep',
        username => 'sara2005',
        default_expires_in => '30 minutes',
        auto_purge_interval => '4 hours',
       });
}

sub get_session_id {
    require Digest::MD5;

    Digest::MD5::md5_hex(Digest::MD5::md5_hex(time().{}.rand().$$));
}
[download]

If $ENV{PATH} is defined (line 0) in the perl script, the code works fine but if $ENV{PATH} is removed, everything goes weird. All the browser returns is a blank screen!!!!!

Any thoughts?

I have encountered a similar problem and attribute itto some manner of locking or race issue between the two processes using Cache::FileCache. Preliminary investigation indicates that CGI::Session may manage the situation better. It is certinally easier to use because it generates the session ID for you.

It is importnt to call flush () whenever you want to push data from the long running process back to the monitoring process however.

How poking at PATH could alter things I have no idea however!

---

DWIM is Perl's answer to Gödel