use warnings;
use strict;

my %fed;
open my $fd, '<', 'file2' or die "open: $!";
$fed{$1}++ while <$fd> =~ m/^(\w+)\s/;
close $fd;

open $fd, '<', 'file1' or die "open: $!";
open my $fd2, '>', '/tmp/file1.tmp' or die "open: $!";  ## FIXME: tmpfile
while (<$fd>) {
  m/^(\w+)\s+(\d+)$/;
  printf $fd2 "$1\t%d\n", exists $fed{$1} ? $2+1 : $2;
}
close $fd2; close $fd;
rename '/tmp/file1.tmp', 'file1' or warn "rename: $!";