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

$ perl --version
This is perl, v5.8.5 built for i386-linux-thread-multi

$ /usr/sbin/httpd -v
Server version: Apache/2.0.52 Server built: Jan 30 2007 09:56:53

$ cat /etc/redhat-release
Red Hat Enterprise Linux ES release 4 (Nahant Update 5)

From a Linux bash command line I invoke a1 with some command line args. a1 uses CGI param() to parse these args - no problems.

From the command line I invoke a2 with some command line args. a2 uses CGI param() to parse these args - no problems.

Change a1 so that it also invokes 'a2 with some command line args'. This instance of a2 can still parse args - no problems.

BUT invoked via a web browser a1 (still calls a2) can use param() to parse args but a2 seems to not be able to.

Here is a1.cgi

#!/usr/bin/perl -wl
use CGI;
use CGI::Carp qw(warningsToBrowser fatalsToBrowser);
use strict;
use diagnostics;

my $q = new CGI;
my $v1 = $q->param('v1') || '';
my $hdr = "I am a1.cgi:";

print $q->header;
print "$hdr v1=$v1<br>";

my $cmd = './a2.cgi v2=dog 2>&1';
print "$hdr cmd = $cmd<br>";
my $cmdOut = qx[$cmd];

print "$hdr cmdOut = <br>$cmdOut<br>";

[download]

Here is a2.cgi

#!/usr/bin/perl -wl
use CGI;
use CGI::Carp qw(warningsToBrowser fatalsToBrowser);
use strict;
use diagnostics;

my $q = new CGI;
my $v2 = $q->param('v2') || '';
my $hdr = "&nbsp;&nbsp;I am a2.cgi:";

print "$hdr from param() v2=$v2<br>";
print "$hdr my cmd line args: @ARGV<br>";

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Here is terminal session usage and output from a1.cgi # PASS

$ ./a1.cgi v1=box
Content-Type: text/html; charset=ISO-8859-1


I am a1.cgi: v1=box<br>
I am a1.cgi: cmd = ./a2.cgi v2=dog 2>&1<br>
I am a1.cgi: cmdOut = <br>&nbsp;&nbsp;I am a2.cgi: from param() v2=dog
+<br>
&nbsp;&nbsp;I am a2.cgi: my cmd line args: v2=dog<br>
<br>

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Here is terminal session usage and output from a2.cgi # PASS

$ ./a2.cgi v2=dog 2>&1
&nbsp;&nbsp;I am a2.cgi: from param() v2=dog<br>
&nbsp;&nbsp;I am a2.cgi: my cmd line args: v2=dog<br>

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Here is browser output from web server url http://somewhere/a1.cgi?v1=box # FAIL

I am a1.cgi: v1=box
I am a1.cgi: cmd = ./a2.cgi v2=dog 2>&1
I am a1.cgi: cmdOut = 
  I am a2.cgi: from param() v2=
  I am a2.cgi: my cmd line args: v2=dog

[download]

As you can see, a1.cgi succeeds but a2.cgi fails to parse it's args via param(), when run by my 'simple' Apache web server.

I EXPECTED a2.cgi to sucessfully use param() regardless of my 3 invocation methods: 2 interactive + 1 apache.

This behavior is naively unexpected by me; can somebody please explain this mechanism?

Replies are listed 'Best First'.
Re: CGI with nested apps, each calling param() to get their args
by Anonymous Monk on Oct 12, 2012 at 02:04 UTC

    This behavior is naively unexpected by me; can somebody please explain this mechanism?

    You're expecting too much from a debugging feature of CGI.pm

    The CGI protocol communicates through %ENV , and each child process gets the same %ENV as parent process, so to CGI.pm won't use the debugging freature and look at @ARGV

    But since CGI programs don't populate @ARGV you can use 

    #!/usr/bin/perl  --
use strict;
use warnings;

use CGI ();

Main( @ARGV );
exit( 0 );

sub Main {
    my $cgi = @_ ? CGI->new(@_) : CGI->new;
}

    [download]

    Or it might be prudent to use GetOpt::Long / --query=a=1;b=2;c=3... instead of testing only for @ARGV

[reply]
[d/l]

      Thank you very much for the simple & elegant solution to my problem. I understand your code.

      I'll be looking in the CGI man page to see where (the equivalent of?) this permitted type of arg-passing is mentioned since I totally missed it.
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