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

Hi
I'm trying to pass arguemnts to a child.pl script via a parent script. My child script is as follows -
#!/usr/bin/perl -w
use strict;

$|++;

use CGI;
my $cgi = CGI->new;
my $number = $cgi->param('number');

print "param: ".$number."\n";

my $n;
print "Command line reporter\n";print "Called with ",$#ARGV+1,"
parameters which ",        @ARGV == 1 ? "was" : "were" ,"\n";print
(++$n,": $_\n") foreach (@ARGV) ;

for(my $i=0;$i<$number;$i++)
{
        print("*\n");
        sleep 1;
}

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when I run this script from the command line, as follows -
 perl child.pl number=4
I get -
param: 4
Command line reporter
Called with 1
parameters which was
1: number=4
*
*
*
*

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But when I call it from the parent script as follows -
exec '/usr/bin/perl', '-T', 'child.pl', 'number=10' or
 die "Cannot execute : $!";

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I get - 
Use of uninitialized value in concatenation (.) or string at child.pl 
+line 10.
param: 
Command line reporter
Called with 1 
parameters which was
1: number=10
Use of uninitialized value in numeric lt (<) at child.pl line 17.

[download]

ARGV works, but not param, what am I doing wrong?
Thanks in advance.

Replies are listed 'Best First'.
Re: Passing Args via Exec
by superfrink (Curate) on Aug 28, 2004 at 01:54 UTC
    Works for me with v5.8.0 (Slackware 9.1 install) What version of CGI.pm are you using? print CGI->version; prints 2.81 for me.

    Update: I didn't read thing clear enough but I think it still works.
    [frink@truth ~/code/perl]$perl 386513.pl number=4
param: 4
Command line reporter
Called with 1
parameters which was
1: number=4
*
*
*
*
[frink@truth ~/code/perl]$perl 386513.pl-exec 
param: 4
Command line reporter
Called with 1
parameters which was
1: number=4
*
*
*
*
[frink@truth ~/code/perl]$cat 386513.pl-exec
#!/usr/bin/perl

exec '/usr/bin/perl', '-T', '386513.pl', 'number=4' or
 die "Cannot execute : $!";

[frink@truth ~/code/perl]$perl -v

This is perl, v5.8.0 built for i486-linux

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[select]
      CGI Version 3.05
      I tried - 
      #!/usr/bin/perl

exec '/usr/bin/perl', '-T', '386513.pl', 'number=4' or
 die "Cannot execute : $!";

      [download]
      and it worked when I called the above from the command line. My calling script must be the problem so, and I run it using my browser. Here it is, can you see the problem? The code is a simple rework of - http://www.stonehenge.com/merlyn/LinuxMag/col39.html 
      #!/usr/bin/perl -w

use strict;

$|++;
 
 $ENV{PATH} = "/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local
+/sbin";
 
 use CGI qw(:all delete_all escapeHTML);
 
 sub show_form {
 print header, start_html("Traceroute"), h1("Traceroute");
 print start_form;
 print submit('traceroute to this host:'), " ", textfield('host');
 print end_form, end_html;
 }
 
 sub get_cache_handle {
 require Cache::FileCache;
 
 Cache::FileCache->new
 ({
 namespace => 'tracerouter',
 username => 'nobody',
 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().$$));
 } 



 if (my $session = param('session')) { # returning to pick up session 
+data
 my $cache = get_cache_handle();
 my $data = $cache->get($session);
 unless ($data and ref $data eq "ARRAY") { # something is wrong
 show_form();
 exit 0;
 }


 print header(),
 start_html(-title => "Traceroute Results",
  ($data->[0] ? () :
  (-head => ["<meta http-equiv=refresh content=5>"])));
 print h1("Traceroute Results");
 print pre(escapeHTML($data->[1]));
 print p(i("... continuing ...")) unless $data->[0];
 print end_html;
 } elsif (my $host = param('host')) { # returning to select host
 if ($host =~ /^([a-zA-Z0-9.\-]{1,100})\z/) { # create a session
 $host = $1;  # untainted now
 my $session = get_session_id();
 my $cache = get_cache_handle();
 $cache->set($session, [0, ""]); # no data yet
 
 if (my $pid = fork) { # parent does
 delete_all(); # clear parameters
 param('session', $session);
 print redirect(self_url());
 } elsif (defined $pid) { # child does
 close STDOUT; # so parent can go on
 unless (open F, "-|") {
 open STDERR, ">&=1";

exec '/usr/bin/perl', '-T', 'child.pl', 'number=4' or
 die "Cannot execute : $!";


 }
 my $buf = "";
 while (<F>) {
 $buf .= $_;
 $cache->set($session, [0, $buf]);
 }
 $cache->set($session, [1, $buf]);
 exit 0;
 } else {
 die "Cannot fork: $!";
 }
 } else {
 show_form();
 }
 } else {  # display form
 show_form();
 }
 
 exit 0;

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[select]
        OK, I'm now trying the following parent called new3.cgi - 
        #!/usr/bin/perl -w

use strict;

$|++;

$ENV{PATH} = "/bin:/sbin:/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/
+sbin";

use CGI qw(:all delete_all escapeHTML);

print header(),
start_html(-title => "Traceroute Results");
print h1("Traceroute Results");

#open STDERR, ">&=1";

exec '/usr/bin/perl', '-T', 'child.pl', 'number=4' or die "Cannot exec
+ute : $!";

print end_html;

        [download]

        I call this on the command line with perl new3.cgi and get -
        Content-Type: text/html; charset=ISO-8859-1

<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html
        PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
         "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en-US" xml:lang="en-U
+S"><head><title>Traceroute Results</title>
</head><body><h1>Traceroute Results</h1>param: 4
Command line reporter
Called with 1
parameters which was
1: number=4
*
*

        [download]
        I then call this with my browser and get -
        Traceroute Results
param: Command line reporter Called with 1 parameters which was 1: num
+ber=4 * *

        [download]

        but if I uncomment the line - open STDERR, ">&=1"; I get -
        Traceroute Results
Use of uninitialized value in concatenation (.) or string at child.pl 
+line 10. param: Command line reporter Called with 1 parameters which 
+was 1: number=4 * *

        [download]

        The command line call is working fine, the browser calls are not
        So I'm guessing my problem has something to do with buffering. Any suggestions?
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Re: Passing Args via Exec
by El Linko (Beadle) on Aug 28, 2004 at 00:10 UTC
    This seems to be working fine for me on linux using perl 5.6.1. What version of perl are you using?
[reply]
      v5.8.4
[reply]
        I'm lost, what should I do? Thanks.
[reply]

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