use strict;

my ( $file1, $file2 ) = @ARGV;
# (getting file names from command line is better than hard-coding them)

# read file2 first, to get the keys and data to test against

my %refdata;

open( F, $file2 ) or die "$file2: $!";
while (<F>) {
    my ( $key, $data ) = split( /,/, $_, 2 );  # (in case key is not 4 digits)
    $refdata{$key} = $data;
}

# now read file1, and output lines that meet the spec

open( F, $file1 ) or die "$file1: $!";
while (<F>) {
    my ( $key, $data ) = split( /,/, $_, 2 );
    print if ( !exists( $refdata{$key} ) or $data eq $refdata{$key} );
}
# (use the command line to redirect output to a "final" file -- e.g.:
#
#    shell>  perl your_script file1 file2 > final
#
# again, it's better than hard-coding another file name