my $filter = "filter";   # I'm a scalar here..

##</code><code>##

$hash{$filter[$c]->[4]}    # or am I an array?

##</code><code>##

'$hash{$filter[$c]->[4]}'   # that will literally be "$hash{$filter[$c]->[4]}"

##</code><code>##

$ ./booboo.pl 
Global symbol "$num_elements" requires explicit package name at ./booboo.pl line 14.
Global symbol "%hash" requires explicit package name at ./booboo.pl line 18.
Global symbol "@filter" requires explicit package name at ./booboo.pl line 18.
Global symbol "%hash" requires explicit package name at ./booboo.pl line 25.
Global symbol "@filter" requires explicit package name at ./booboo.pl line 25.
Global symbol "@filter" requires explicit package name at ./booboo.pl line 25.
syntax error at ./booboo.pl line 26, near "+]"
  (Might be a runaway multi-line "" string starting on line 25)
Global symbol "$line" requires explicit package name at ./booboo.pl line 28.
Global symbol "%hash" requires explicit package name at ./booboo.pl line 34.
Global symbol "@filter" requires explicit package name at ./booboo.pl line 34.
Global symbol "@filter" requires explicit package name at ./booboo.pl line 34.
Global symbol "@filter" requires explicit package name at ./booboo.pl line 34.
Global symbol "$line" requires explicit package name at ./booboo.pl line 37.
Missing right curly or square bracket at ./booboo.pl line 49, at end of line
./booboo.pl has too many errors.