#!/usr/bin/perl -w

use strict;

my $Usage = "Usage: $0 line_count input.file output_name\n";
( @ARGV == 3 and $ARGV[0] =~ /^\d+$/ and -f $ARGV[1] )
    or die $Usage;

my ( $line_limit, $infile, $outname ) = @ARGV;
my $outid = 0;

open( I, $infile ) or die "$0: open for input failed on $infile: $!\n$Usage";
while (<IN>) {
    if ( $. % $line_limit == 1 ) {
        close OUT if ( $outid );
        my $outfile = sprintf( "%s.%03d", $outname, ++$outid );
        open( OUT, ">", $outfile ) or die "$0: open for output failed on $outfile\n";
    }
    print OUT;
}
close OUT;