apart from the answers given so far,

my @gser=('TME GSER', $dealn, 'PAS 927922','SO',$so);
my $gser2= join ';', $gser[0],$gser[1],$gser[2],$gser[3],$gser[4];
worksheet->write_string(2, 4, $gsers); #input string into excel cell
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- do you really mean $gsers in the last line? shouldn't that be $gser2 ?

Be consistent, above all ;-)