open (IN, 'mv_0000001.txt') or die "$!"; 
while(<IN>){ 
    here you read/parse the lines of the file 
} 
close IN

my %cid1_rate = {/ls=a\w ls=a\w qw//[],/n qw//[],/n};

use strict; 
use warnings; 
my %cid1_rate = (); #declare the hash 
open (IN, 'mv_0000001.txt') or die "$!"; 
while(<IN>){ 
     next if /^\s*1:/; #skip the line that starts with 1 
     my ($key,$val) = (split ',') [0,1]; 
     $cid1_rate{$key} = $val;  
} 
close (IN); 
foreach my $key (keys %cid1_rate) { 
    print "key = $key,  value = $cid1_rate{$key}\n"; 
}

     my ($key,$val) = (split ',') [0,1]; <--- an array slice 
     $cid1_rate{$key} = $val;

     my ($key,$val,undef) = split ','; 
     $cid1_rate{$key} = $val;

my %h; 
<DATA>; # skip first line 
while(<DATA>){ 
   my ($k,$v) = (split ',')[0,1]; 
   $h{$k}=$v; 
} 
 
print scalar keys %h; #prints the number of keys - 548