bos-mp96h:~ jvx$ head asgn.txt  
ra_uuid: a37bbde8-36ba-11e8-a697-00e081ea0e98
cms_uuid: 2d937c7e-36ba-11e8-91f1-00e081ea0e8e
mpd_uuid: 6edd7a68-36b0-11e8-a120-00e081ea0e5c
amLeader: 1
numAssignments = 20956857
mpg=1 mrule=140 reg=7989 score=10625 rank=0 perc=100 mp_demand=40
mpg=2 mrule=140 reg=7989 score=10625 rank=0 perc=100 mp_demand=40
mpg=3 mrule=150 reg=7989 score=0 rank=0 perc=100 mp_demand=20
mpg=4 mrule=150 reg=7989 score=10625 rank=0 perc=100 mp_demand=40

##</code><code>##

#! /usr/bin/perl -w
use strict;
use warnings;
use Data::Dumper ; 

my $source = shift ;
my $lines_per_file = shift ; 

 open (my $FH, "<$source") or die "Could not open source file. $!";
 open (my $OUT, '>', '00000000.log') or die "Could not open destination file. $!";

my $i = 0;
my $index_last = 0 ;
my $index_current = 0;  

while(my $line = <$FH>) {
	next unless ($line =~ /mrule/) ; 
	if ($line =~ /mrule=([0-9]+)/){
		print $OUT $line; 
		$i++ ;

		if ($1 != $index_last){
        		$index_current = $1 ; 
        		close($OUT); 
        		my $NEW = sprintf("%08d", $index_current);
        		open($OUT, ">${NEW}.log") or die "Could not open destination file. $! " ; 
        		} 
        		$index_last = $index_current ; 
	}
}

close($FH);
close($OUT); 


##</code><code>##

bos-mp96h:~ jvx$ ./partition_file.pl asgn.txt  
Can't use string ("00000140") as a symbol ref while "strict refs" in use at ./partition_file.pl line 26, <$FH> line 6.