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

Hi Monks!
I am trying to run this code and capture its output to a file, the code runs well, but cant get output to a file to work, here is what I am testing with: 
#!/usr/bin/perl

use strict;
use warnings;
use File::Slurp;
use Data::Dumper;

$| = 1;


# Encrypt file.

my $gpg_command = `gpg --trust-model always -er 12345678 my_file.txt`;

print defined($gpg_command) ? $gpg_command : "Command failed\n";


# Capture STDOUT and save it to a file.

open(READ, "$gpg_command 2>&1 |") or die "Failure on open $!\n";

 open( my $out, ">", "encrypted.pgp" ) or die "Could not open file for
+ encrypted data - $!";

  while (<READ>) {

    my $output .= $_;
    print $out $output;
    
  }

close $out or die "1 Failure on close $!\n";; 
close (READ) or die "2 Failure on close $!\n";

print "\nDone.\n";

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Thanks for looking!

Replies are listed 'Best First'.
Re: Capture response from backticks to a file.
by kcott (Archbishop) on Nov 13, 2013 at 20:04 UTC

    On my system, gpg returns 0 if there were no problems, 1 otherwise. There's no undef (or equivalent) returned so checking the return value with defined() isn't doing what you appear to think it is.

    Again, on my system, both "-o file" and "--output file" are documented as "Write output to file.". Perhaps that's what you want.

    Type "man gpg" at your command line to see how this is implemented on your system.

    -- Ken

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Re: Capture response from backticks to a file.
by dsb (Chaplain) on Nov 13, 2013 at 19:26 UTC
    I think you're misusing the backticks in your code.

    this bit: 

    my $gpg_command = `gpg --trust-model always -er 12345678 my_file.txt`;

print defined($gpg_command) ? $gpg_command : "Command failed\n"

    [download]
    IS capturing the output from the command and then printing it to STDOUT.

    But in your open command, you're effectively trying to open a pipe to a command that matches the output from your original backtick command, which should be failing I'd think.

    remember that backticks do execute your command, and things get a little simpler. For example: 

    use strict;
use FileHandle;

my $fh = FileHandle->new('capture.out',"w");

print $fh `dir`;

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    dsb
    This @ISA my( $cool ) %SIG
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      It doesn't fail, the backticks executes fine but I can't capture the result to a file still.
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        I agree with dsb. You've already run the pgp command and have capured it's output in $gpg_command. Sorry to be dense, but what are you hoping to achieve from the rest of your script?
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Re: Capture response from backticks to a file.
by marinersk (Priest) on Nov 13, 2013 at 21:17 UTC
    I would change: 
    # Encrypt file.
my $gpg_command = `gpg --trust-model always -er 12345678 my_file.txt`;
print defined($gpg_command) ? $gpg_command : "Command failed\n";

# Capture STDOUT and save it to a file.
open(READ, "$gpg_command 2>&1 |") or die "Failure on open $!\n";

 open( my $out, ">", "encrypted.pgp" ) or die "Could not open file for
+ encrypted data - $!";

    [download]

    to: 

    # Build encryption command
my $gpg_command = "gpg --trust-model always -er 12345678 my_file.txt";

# Execute command and capture STDOUT.
my $gpg_results = `$gpg_command`;
print defined($gpg_results) ? $gpg_results : "Command failed\n";

# Save captured STDOUT to a file.
open( my $out, ">", "encrypted.pgp" ) or die "Could not open file for 
+encrypted data - $!";

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    Then:

    • Correct any errant assumptions about what happens when the command fails;
    • Adjust what you're writing to the output file to reflect what you actually want there.
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