use strict;
use warnings;
 
my $snpFile = <<SNP;
snp_rs              log_1_pval
rs3749375    11.7268615355335
rs10499549    10.4656064706897
rs7837688    9.85374546064131
rs4794737    9.41576680248523
rs10033399    9.36407447191822
rs4242382    9.22809709356544
rs4242384    8.91767075801336
rs9656816    8.61480602028324
rs982354    8.40833878650415
rs31226            8.38047936810042
SNP

my $mapFile = <<MAP;
rs10904494    NP_817124    17881
rs7837688    NP_817124    39800
rs4881551    ZMYND11    21567
rs7909028    ZMYND11    5335
rs10499549    ZMYND11    0
rs12779173    ZMYND11    0
rs2448370    ZMYND11    0
rs2448366    ZMYND11    0
rs2379078    ZMYND11    0
rs3749375    ZMYND11    0
MAP

my %snpLookup;

# Populate the hash
open my $snpIn, '<', \$snpFile or die "Can't open snp file: $!";
/^(\w+)\s+(\d+\.\d+)/ and $snpLookup{$1} = $2 while <$snpIn>;
close $snpIn;

# Perform the search and report
open my $mapIn, '<', \$mapFile or die "Can't open map file: $!";
/^(\w+)\s+(\w+)/ and exists $snpLookup{$1} and print "$1    $2\n"
    while <$mapIn>;
close $mapIn;

##</code><code>##

rs7837688    NP_817124
rs10499549    ZMYND11
rs3749375    ZMYND11