How can I suppress STDOUT temporarily in a Perl program?
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21-09-2019 - |
Question
Is there any easy way to tell perl "now ignore everything that is printed"?
I have to call a procedure in an external Perl module, but the procedure prints a lot of unnecessary information (all through standard print).
I know select can be used to redirect it somehow, but I am not too wise from reading perldoc on it.
edit: I found the answer sooner, but I will add an example to make it clearer (but not much I guess)
use TectoMT::Scenario;
use TectoMT::Document;
sub tagDocuments {
my @documents = @_;
my $scenario = TectoMT::Scenario->new({'blocks'=> [ qw(
SCzechW_to_SCzechM::Sentence_segmentation
SCzechW_to_SCzechM::Tokenize
SCzechW_to_SCzechM::TagHajic
SCzechM_to_SCzechN::Czech_named_ent_SVM_recognizer) ]});
$scenario->apply_on_tmt_documents(@documents);
return @documents;
}
TectoMT::Scenario and TectoMT::Document are those external modules
Solution
My own answer:
use IO::Null;
print "does print.";
my $null = IO::Null;
my $oldfh = select($null);
print "does not print.";
select($oldfh);
print "does print.";
OTHER TIPS
I realise that this has been answered, but I think it's worth knowing about an alternative method of doing this. Particularly if something is hell-bent on printing to STDOUT
…
# Store anything written to STDOUT in a string.
my $str;
open my $fh, '>', \$str;
{
local *STDOUT = $fh;
code_that_prints_to_stdout();
}
The key bit is local *STDOUT
. It replaces the normal STDOUT
with a filehandle of your choosing, but only for the scope of the block containing the local.
Referring to some answers here and on other threads, I came up with this;
use strict;
use warnings;
use File::Spec;
sub my_functor { system("some_noisy_command.exe", "--option1", "--option2"); }
silently(\&my_functor);
Where "silently()" takes a functor and runs it with stdout redirected:
sub silently($) {
#Turn off STDOUT
open my $saveout, ">&STDOUT";
open STDOUT, '>', File::Spec->devnull();
#Run passed function
my $func = $_[0];
$func->();
#Restore STDOUT
open STDOUT, ">&", $saveout;
}
open my $saveout, ">&STDOUT";
open STDOUT, '>', "/dev/null";
(do your other stuff here)
open STDOUT, ">&", $saveout;
If you want to use only modules in the standard library, File::Spec
has the devnull()
function. It returns a string representing the null device ("/dev/null"
on *nix) that you can presumably open with open()
.