in reply to Re: Handling the output of a system command -- how to best manage?
in thread Handling the output of a system command -- how to best manage?

Greetings, and thank you for your reply.
After adding
print "Content-type: text/html\n\n";
I attempted to use your example, however, it failed to produce any output (to the browser).
Perl complained (rightfully) about
( Insecure $ENV{PATH} while running with -T switch )
So modified it as follows: 
use Modern::Perl;

my @l = system(`ls -1b`);
my $c = 0; # toggle for odd/even lines
for (@l){
    chomp;
    my $bg = $c ? "#eee" : "#ccc";
    say qq| <p style="font-family:mono;background:$bg">$_</p> |;
    $c = 0 if $c++ == 1;
}

[download]
Which produces one line with a grey background, that simply has a -1 in it.

I'm confused. Any further thoughts?
Thank you again for your response.



use perl::always;
my $perl_version( 5.12.4 );
print $perl_version;

Replies are listed 'Best First'.
Re^3: Handling the output of a system command -- how to best manage?
by aaron_baugher (Curate) on Jun 21, 2012 at 03:18 UTC

    Why did you change my line:

    my @l = `ls -1b`;

    to:

    my @l = system(`ls -1b`);

    ? Mine runs the ls command in a subshell and returns the results to the @l array, one line per array element. Yours runs ls in a subshell and captures the output, but then passes that output to system, which tries to run that in another sub-process, passing the return value of that sub-process to @l, making it the first (and only) element. Odds are very good that a listing of the files in your directory doesn't make a valid system command (and could possibly make a harmful one), so the return value is an error number, in this case, -1, 'failed to execute'.

    See perlipc and other docs on the difference between system and backticks, as well as other ways to run a sub-process and capture the output, like opening a pipe:

    open my $pipe, '-|', 'ls -1b' or die $!;
while(<$pipe>){
  chomp;
  say qq| <tag attr='value'>$_</tag> |;
}
close $pipe;

    [download]

    There are a lot of different ways to do this. Perl isn't called a glue language for nothing. But some are usually better than others, depending on the circumstances.

    Aaron B.
    Available for small or large Perl jobs; see my home node.

[reply]
[d/l]
[select]

      Greetings, and thank you for taking the time to help me on this.
      EUREKA!
      I maintained the previous revisions I made to your original reply. But,
      removed the system() call -- retuning it to `ls -1b`;

      It appears that the only issue I had with yours originally, was the single quote marks used in the HTML
      formatting -- ' vs ".
      For clarity (and anyone else that might be interested): 

      #!/usr/bin/perl
print "Content-type: text/html\n\n";
use strict;
use diagnostics -verbose; # Desperately seeking guidance :P

use Modern::Perl;

my @l = `ls -1b`;
my $c = 0; # toggle for odd/even lines
for (@l){
    chomp;
    my $bg = $c ? "#eee" : "#ccc";
    say qq| <p style="font-family:mono;background:$bg">$_</p> |;
    $c = 0 if $c++ == 1;
}
# use strict; with use Modern::Perl; is redundant
# keeping use strict; and commenting use Modern Perl;
# would require changing "say" to "print"

      [download]

      Thank you VERY much. The output is beautiful! :)

      #!/usr/bin/perl -Tw
use perl::always;
my $perl_version = "5.12.4";
print $perl_version;
[reply]
[d/l]

        You're welcome! I use single quotes around HTML attribute values all the time, so I'm not sure why that would have caused a problem, but I'm glad you got it working.

        Aaron B.
        Available for small or large Perl jobs; see my home node.

[reply]

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