comment on

I see that the STDOUT/STDERR problem has been explained. Here's some additional comments.

Always start your code with the strict and warnings pragmata.
Let Perl do the I/O exception handling for you with the autodie pragma.
You'll need to escape characters that are special to HTML (e.g. change '&' to '&'). In the code below, I used HTML::Escape.
Use lexical variables for your filehandles. Package variables have pretty much the same problems as global variables and should generally be avoided.
Use the 3-argument form of open(). For this particular exercise, see the "Opening a filehandle into a command" section.
Aim to not leave filehandles open any longer than is absolutely necessary. In the code below, see how I achieved this using an anonymous block.
Tip: With 'chomp $_; print "$_\n";' you've removed the newline in the first statement then added it back in the next. The chomp and subsequent \n are both unnecessary. As many Perl functions use $_ in the absence of any other expression, $_ is unnecessary in both statements. You could have written that four-line (six-line if you include the two lines of pointless whitespace) while loop as the one-line: 'print while <runmain>;'; compare with my "print escape_html($_) while <$cmd_pipe>;" (in the code below).
If you lay out your code with consistent indentation, it will be easier to read; in addition, this will often highlight logic errors.

Here's some output from my command line:

$ ls -al a_real_dir
total 4
drwxr-xr-x 1 ken None 0 Nov 19 18:20 .
drwxr-xr-x 1 ken None 0 Nov 19 19:10 ..
-rw-r--r-- 1 ken None 0 Nov 19 18:20 demo_file_A
-rw-r--r-- 1 ken None 0 Nov 19 18:20 demo_file_B

$ ls -al not_a_real_dir
ls: cannot access 'not_a_real_dir': No such file or directory
[download]

Here's a demo script that uses all of the points I raised:

#!/usr/bin/env perl

use strict;
use warnings;
use autodie;

use HTML::Escape 'escape_html';

my %commands = (ls => '/usr/bin/ls -al');
my @targets = qw{a_real_dir not_a_real_dir};
my $program = 'ls';

print "<html>\n<head>...</head>\n<body>\n";

for my $target (@targets) {
    my $cmd = "$commands{$program} $target 2>&1";
    print '<h1>', escape_html($cmd), "</h1>\n<pre>\n";

    {
        open my $cmd_pipe, '-|', $cmd;
        print escape_html($_) while <$cmd_pipe>;
    }

    print "</pre>\n";
}

print "</body>\n</html>\n";
[download]

Output:

<html>
<head>...</head>
<body>
<h1>/usr/bin/ls -al a_real_dir 2&gt;&amp;1</h1>
<pre>
total 4
drwxr-xr-x 1 ken None 0 Nov 19 18:20 .
drwxr-xr-x 1 ken None 0 Nov 19 19:10 ..
-rw-r--r-- 1 ken None 0 Nov 19 18:20 demo_file_A
-rw-r--r-- 1 ken None 0 Nov 19 18:20 demo_file_B
</pre>
<h1>/usr/bin/ls -al not_a_real_dir 2&gt;&amp;1</h1>
<pre>
/usr/bin/ls: cannot access &#39;not_a_real_dir&#39;: No such file or d
+irectory
</pre>
</body>
</html>
[download]

"I have omitted a lot of the header and html code, ..."

That's fine. My code is only intended as a demo example: adapt to your needs.

— Ken

In reply to Re: null output on program by kcott
in thread null output on program by Nobby

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