Correct way to capture command output to a file in Perl.

perl514 has asked for the wisdom of the Perl Monks concerning the following question:

Respected Monks,

I need to redirect the command output to a file in a Perl Script. So far, I have come across the following two ways to do it:


use warnings;
use strict;
open(PS,"ping localhost|") || die "Failed: $!\n";
while ( <PS> )
{
  #-- do something here
}
[download]

Another method is:

use warnings;
use strict;
open (my $file, '>', 'output.txt') or die "Could not open file: $!";
my $output = `example.exe`; 
die "$!" if $?; 
print $file $output;
[download]

Please let me know which is the correct way to capture the output. I know there is more than one way to do what I am looking for, but which one of these two are correct in sort of a "Best Practice" way? Thwack me on the head if I am thinking too much and this is trivial :)

Perlpetually Indebted To PerlMonks

use Learning::Perl;
use Beginning::Perl::Ovid;
print "Awesome Books";
[download]

http://dwimperl.com/windows.html is a boon for Windows.

Comment on Correct way to capture command output to a file in Perl. Select or Download Code

Replies are listed 'Best First'.
Re: Correct way to capture command output to a file in Perl. by davido (Cardinal) on May 01, 2013 at 19:31 UTC
Have you looked at Capture::Tiny? ...a third way, but it works great. From the synopsis: `use Capture::Tiny ':all'; # capture from external command ($stdout, $stderr, $exit) = capture { system( $cmd, @args ); };` [download] Dave	[reply] [d/l]
Re: Correct way to capture command output to a file in Perl. by Laurent_R (Canon) on May 01, 2013 at 19:58 UTC
If you want to capture the output of system command, you can simply use the backticks: my @list_of_files = `ls -l`;	[reply] [d/l]
Re: Correct way to capture command output to a file in Perl. by kcott (Archbishop) on May 02, 2013 at 00:35 UTC
G'day perl514, I'm wondering if the following was closer to what you had in mind: `perl -Mstrict -Mwarnings -E ' my $cmd = q{ping -c 5 www.perlmonks.org}; my $file = q{./pm_1031633.out}; open my $ping_pipe, "-\|", $cmd or die "Pipe from $cmd failed: $!"; open my $out_fh, ">", $file or die "Write to $file failed: $!"; while (<$ping_pipe>) { print { $out_fh } $_; } '` [download] $ cat ./pm_1031633.out PING perlmonks.org (66.39.54.27): 56 data bytes 64 bytes from 66.39.54.27: icmp_seq=0 ttl=45 time=264.646 ms 64 bytes from 66.39.54.27: icmp_seq=1 ttl=45 time=266.345 ms 64 bytes from 66.39.54.27: icmp_seq=2 ttl=45 time=266.284 ms 64 bytes from 66.39.54.27: icmp_seq=3 ttl=45 time=266.134 ms 64 bytes from 66.39.54.27: icmp_seq=4 ttl=45 time=263.832 ms --- perlmonks.org ping statistics --- 5 packets transmitted, 5 packets received, 0.0% packet loss round-trip min/avg/max/stddev = 263.832/265.448/266.345/1.023 ms [download] See open for many more examples. -- Ken	[reply] [d/l] [select]
Re: Correct way to capture command output to a file in Perl. by BillDowns (Novice) on May 01, 2013 at 20:26 UTC
I would probably just use Windows redirection: `example.exe >output.txt`;Then read that file.	[reply] [d/l]
Re^2: Correct way to capture command output to a file in Perl. by morgon (Priest) on May 02, 2013 at 15:02 UTC
If you do it like that you would not use backticks but system() as you would not capture any output. But I would not do it like that as in the error-case it is more difficult to determine what went wrong (e.g. the command you call may be able to run, but may not be able to write to the file).	[reply]
Re: Correct way to capture command output to a file in Perl. by bimleshsharma (Beadle) on May 02, 2013 at 07:38 UTC
See, in your first set of code it will display output on screen instead of writing into file. Second way is good to use.	[reply]
Re: Correct way to capture command output to a file in Perl. by perl514 (Pilgrim) on May 02, 2013 at 15:56 UTC
Venerable Monks, Thank you all for taking time to reply. Thank you very much Perlpetually Indebted To PerlMonks `use Learning::Perl; use Beginning::Perl::Ovid; print "Awesome Books";` [download] http://dwimperl.com/windows.html is a boon for Windows.	[reply] [d/l]

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