Thank you very much for your reply. Here is the original code:

use strict;
use warnings;
open my $fh, '<', 'kegg_pathway_title.txt' or die $!;
my %dict =  map { chomp; split ' ', $_, 2 } <$fh>;
my $re = join '|', keys %dict;
open $fh, '<', 'Orthogroups_3.csv' or die $!;
while (<$fh>) {
  s/($re)/$dict{$1}/g;
  print;
}
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I added the line

next if $. < 2;
[download]

because it giving me more column than the original csv. My original csv contains 13 columns. After replacing the content using dictionary it gives me many more column and couldn't load in R. You saw my previous code in loading the file in R. Is there anything I need to do to make it loadable in R. The 2nd column of the dict may contain multiple name. In the original csv the cells also contains single/multiple or no entry. Thanks again for helping me. Best Regards Zillur