If i understood your question correctly, is this you want?

$input = $ARGV[0];

undef $/;
$str = <DATA>;

while ($str =~ /(template?\d+)[^}]+}/gsi)
{
    
    $hash{$1} = $&;
}

%temp = ('test1' => "template2", 'test2' => "template3", 'test1,test2'
+ => "template1");


@a= keys %hash;
@m= grep /^$temp{$input}$/, @a;
print "$m";
if (@m)
{
    print "$hash{$m[0]}" ;
}
else
{
    print "$hash{'template4'}";
}
#print "$_\t$hash{$_}\n" for keys %hash;
__DATA__
template1(test1,test2) {
  variable_1 : input;
  index_1(" 1.0, 2.0");
  index_2(" 1.0, 2.0");
}
template2(test1,!test2) {
  variable_1 : output;
  index_1(" 1.0, 2.0");
  
}
template3(!test1,test2) {
  variable_1 : time;
  index_2(" 1.0, 2.0");
}
template4(!test1,!test2) {
  variable_1 : time;
  index_1(" 1.0, 2.0");
}
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updated: