Capture response from backticks to a file.

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";
[download]

Thanks for looking!

Comment on Capture response from backticks to a file. Download Code

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	[reply] [d/l] [select]
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`; [download] dsb This `@ISA my( $cool ) %SIG`	[reply] [d/l] [select]
Re^2: Capture response from backticks to a file. by Anonymous Monk on Nov 13, 2013 at 19:40 UTC
It doesn't fail, the backticks executes fine but I can't capture the result to a file still.	[reply]
Re^3: Capture response from backticks to a file. by astroboy (Chaplain) on Nov 13, 2013 at 19:53 UTC
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?	[reply]
Re^4: Capture response from backticks to a file. by Anonymous Monk on Nov 13, 2013 at 20:03 UTC
Re^4: Capture response from backticks to a file. by Anonymous Monk on Nov 13, 2013 at 20:28 UTC
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 - $!"; [download] 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.	[reply] [d/l] [select]


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