haukex (++) is right - the evaluation depends on the contents of

$ctxt{'capi_devices'}
[download]

I was able to get "expected output" after setting:

$ctxt{capi_devices}=["CAPI DEVICE"];
[download]

The value of $inp (After first iteration) was:

afu_op=grpcapp
capp=1
icnt=200
capi_dev=CAPI DEVICE
capi_cards=1

<%=
my $marega = \'\';
if (@{$ctxt{\'test\'}}){
$marega =
\'splthid=\' . join(\' \' ,@spthid_a). "\\n" .
\'splthjobops=\' . join(\' \', @{$ctxt{\'test\'}}). "\\n" ;
}
$marega;
%>
[download]