seq implementation in perl

seq.pl

#!/usr/bin/env perl
use strict;
use warnings;

my @args = @ARGV;
my %opt;

$opt{f} = '%g';

foreach (@args) {
    if ($_ =~ /^-(\D)$/) {
        shift @args;
        $opt{$1} = shift @args;
    }
    else {
        last;
    }
}

my ($first, $increment, $last) = (1, 1, 1);
if (scalar @args == 1) {
    $last = $args[0];
}
elsif (scalar @args == 2) {
    $first = $args[0];
    $last  = $args[1];
}
elsif (scalar @args == 3) {
    $first     = $args[0];
    $increment = $args[1];
    $last      = $args[2];
}
else {
    die 'invalid argument(s)';
}

for (
    my $i = $first;
    ($increment > 0) ? $i <= $last : $i >= $last;
    $i += $increment
    )
{
    printf "$opt{f}\n", $i;
}

seq.t

#!/usr/bin/env perl
use strict;
use warnings;
use Test::Base;

plan tests => 1 * blocks;

my $target = $ENV{SEQ_COMMAND};

filters {
    input    => [qw/chomp make_cmd_str exec_perl_stdout/],
    expected => [qw//],
};

sub make_cmd_str {
    return "system '$target @_'";
}

run_is_deeply;

__END__

=== 1 arg (seq 0)
--- input
0
--- expected

=== 1 arg (LAST)
--- input
1
--- expected
1

=== 1 arg (seq 10)
--- input
10
--- expected
1
2
3
4
5
6
7
8
9
10

=== 2 args (FIRST LAST)
--- input
1 10
--- expected
1
2
3
4
5
6
7
8
9
10

=== 3 args (FIRST INCREMENT LAST)
--- input
1 2 5
--- expected
1
3
5

=== negative start (seq -10 0)
--- input
-10 0
--- expected
-10
-9
-8
-7
-6
-5
-4
-3
-2
-1
0

=== null return (seq 10 1)
--- input
10 0
--- expected

=== null return (seq -1 -2)
--- input
-1 -2
--- expected

=== only 0
--- input
0 0
--- expected
0

=== null return (seq -1 -1 1)
--- input
-1 -1 1
--- expected

=== 10 to 1
--- input
10 -1 1
--- expected
10
9
8
7
6
5
4
3
2
1

=== -1 3 10
--- input
-1 3 10
--- expected
-1
2
5
8

=== 10 -4 -2
--- input
10 -4 -2
--- expected
10
6
2
-2

=== format
--- input
-f %02g 0 10 100
--- expected
00
10
20
30
40
50
60
70
80
90
100

seq_error.t

#!/usr/bin/env perl
use strict;
use warnings;
use Test::More;

plan tests => 2;

isnt system($ENV{SEQ_COMMAND}), 0, 'no argumant';
isnt system("$ENV{SEQ_COMMAND} 1 1 1 1"), 0, '4 argumants';