use strict;
use warnings;

use Getopt::Long;

my ($number, $format) = (2, "output");
GetOptions( 
        "number=i" => \$number,
        "format=s" => \$format,
);

my @output_file;
foreach my $num (1..$number) {
        my $file = "$format.$num";
        open( $output_file[$num-1], ">", $file ) or die "Couldn't open
+ '$file' for write: $!\n";
}

my $file_num = 0;
while(<>) {
        print {$output_file[$file_num]} $_;
        $file_num += 1;
        $file_num %= $number;
}
[download]

perl script.pl --format out --number 7 input1 input2 ...
[download]

Right on! thank you for the code thor. If you are interested or have any ideas on how to improve - here are some other (bioinformatics) liners that I have been working with and have put on the site l3v3l's scratchpad

# Choose the Nth FASTA record
# Called as "perl script_name.pl line_number file_name"
use warnings;
use strict;

$/= '>';
my $line_number = shift;
while(<>)
   chomp;
   if ($.-1 == $line_number ) {
      print;
      exit 0;
   }
}
[download]

# Choose any Range of FASTA records
# Called as perl script_name.pl --start start_line --end end_line file
+_name
# both --start and --end are optional;
# no --start => start reading from end of file, end at --end
# no --end => start reading from --start, read to end of file
# neither => print every line
use warnings;
use strict;

use Getopt::Long;
my ($start, $end) = (undef, undef);
GetOptions(
   "start=i" => \$start,
   "end=i" => \$end,
);
$/='>';
while(<>) {
   if(
     (!defined($start) || $start <= $.) &&
     (!defined($end) || $. <= $end)
   ) {
      print;
}
[download]

In reality, the second script subsumes the first as a special case (set start and end to the same value).

As for your "show the number of lines" example, I don't understand it. From the looks of it, it looks like it counts the number of lines in the file that have a whitespace character in it. Is this really what you want?

thor

The only easy day was yesterday