#!/usr/bin/perl

# source: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=961638

=head1 NAME

stocat - stochastic cat, selecting lines with uniform probability


=head1 SYNOPSIS

=over

=item B<stocat> [B<-p>|B<--probability> PROBABILITY] [I<FILE>|B<->]...

=back


=head1 DESCRIPTION

Concatenate FILE(s) to standard output, but printing each input line to output
only with a given probability, defaulting to 0.1 (i.e., 10%).

With no FILE or when FILE is B<->, read standard input.


=head1 OPTIONS

=over 4

=item -p, --probability

Output lines with the given probability, specified as a number between 0 (0%
probability) and 1 (100% probability). Default: 0.1 (i.e., 10% probability).

=back


=head1 SEE ALSO

L<cat(1)>


=head1 AUTHOR

Copyright 2020 by Stefano Zacchiroli <zack@upsilon.cc>

Licensed under the GNU GPL.

=cut

use Getopt::Long;

sub die_usage() {
    die "Usage: $0 [--probability|-p PROBABILITY] [file|-]\n";
}

my $probability = 0.1;
if (! GetOptions("probability|p=f" => \$probability)) {
    die_usage();
}
if ($probability < 0 || $probability > 1) {
    die_usage();
}

while (<>) {
    print $_ if rand() <= $probability;
}