But SHOULD you redirect STDIN?

For a lot of my code, it does one thing at a time, it does it very well, and then it quits. I don’t add a lot of flags or logging or notification, I run it in cron, and the last thing I want is a lot of this was successful emails in my inbox.

So, a module I use a lot is IO::Interactive. There are two main things I use it for.

use strict;
use warnings;
use utf8;
use feature qw{ say };

use Getopt::Long;
use IO::Interactive qw{ interactive is_interactive };

my $verbose;
GetOptions( 'verbose' => \$verbose );

say { interactive } "
        This will only print if running interactive, so you cannot
        redirect this output to a file.
    " ;

say "
        This will print if interactive, or if the -v flag is set,
        which means you can run program -v > logfile or something if
        you really need the output;
    " if $verbose or is_interactive;

While having verbose mode can be useful, I just use {interactive} more often than not, because I just don’t care. If I needed logging, Log::Log4perl is available.

My friend Gizmo asked about that, and wondered about giving a file name. I started wondering about dumping output to files, which lead me to think about redirecting STDOUT.

#!/usr/bin/env perl

use strict;
use warnings;
use utf8;
use feature qw{ postderef say signatures state switch };
no warnings
    qw{ experimental::postderef experimental::smartmatch experimental::signatures };

# Forgive us, Saint Doubt

use Getopt::Long;
use JSON;
use YAML;
use Scalar::Util qw(looks_like_number);
use List::Util qw{uniq uniqnum reduce};

use lib '/home/jacoby/lib';
use oDB;

my $json = JSON->new->pretty->canonical;

my $filename;
GetOptions( 'file=s' => \$filename );

if ( defined $filename ) {
    open STDOUT, '>', $filename;
}

my $data = [];
for my $i ( 0 .. 9 ) {
    for my $j ( 0 .. 9 ) {
        my $k = $i . $j;
        $data->[$i][$j] = $k;
    }
}

say $json->encode($data);

This allows you to go program -f file.json and get that output in a file, rather than program > file.json.

The better thing would be testing on $filename and using YAML’s DumpFile if it contains .yml, or Text::CSV if .csv or whatever format you might want.

Additionally, you could want to see “I’m writing a file” before and “I wrote the file” after, which means you would want to be able to back off that decision.

if ( defined $filename ) {
    my $data = [];
    for my $i ( 0 .. 9 ) {
        for my $j ( 0 .. 9 ) { my $k = $i . $j; $data->[$i][$j] = $k; }
    }
    local (*STDOUT);
    if ( open STDOUT, '>', $filename ) { say $json->encode($data); }
}

But there isn’t anything in that to make it preferable to opening a separate filehandle. I suppose select is doable.

So, St Doubt, I have become befuddled and seek the proper way.

If you have any questions or comments, I would be glad to hear it. Ask me on Twitter or make an issue on my blog repo.