use Text::CSV_XS ();

my %data;

parse_ssn_file( "file1.txt", \%data );
parse_salary_file( "file2.txt", \%data );

my $csv = Text::CSV_XS->new();
foreach my $cur ( sort keys %data ) {
  $csv->combine( $cur,
		 @{ $data{$cur} }{qw( ssn file salary zip )} );
  print $csv->string, "\n"
}

exit 0;

sub parse_ssn_file {
  my( $file, $data ) = @_;
  local( *CUR );

  open( CUR, $file ) or die "Can't open $file: $!\n";

  scalar <CUR>;    # discard header

  my $csv = Text::CSV_XS->new( );

  while( <CUR> ) {
    $csv->parse( $_ );
    my @cur = $csv->fields();

    $data->{ $cur[0] }->{ssn}  = $cur[1];
    $data->{ $cur[0] }->{file} = $cur[2];
  }

  return
}

sub parse_salary_file {
  my( $file, $data ) = @_;
  local( *CUR );

  open( CUR, $file ) or die "Can't open $file: $!\n";

  scalar <CUR>;    # discard header

  my $csv = Text::CSV_XS->new( );

  while( <CUR> ) {
    $csv->parse( $_ );
    my @cur = $csv->fields();

    $data->{ $cur[0] }->{salary} = $cur[1];
    $data->{ $cur[0] }->{zip}    = $cur[2];
  }

  return
}

__END__

##</code><code>##

file1.txt
Name,SSN,File
"Doe, John",123456789,3447
"Flinstone, Fred",000000302,1234

file2.txt
Name,Salary,ZIP
"Flinstone, Fred",34500,90210
"Doe, John",50000,10003

Output:
"Doe, John",123456789,3447,50000,10003
"Flinstone, Fred",000000302,1234,34500,90210