Could you adjust your script to look like

use Data::Dumper;
$Data::Dumper::Useqq = 1;

my $pat = "local_alphabet_string_that_I_copy_from_the_excel_cell_into_
+the_perl_script";
print(Dumper($pat));
print(Dumper($field));
if ($field=~/$pat/){$field=...;}
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and give us the output. It'll tell us which variable is wrong and how it's wrong.