Works for me

>perl -le"@a=qw(a b c d e); undef @a[2,3]; print for @a"
a
b
c

e
[download]

Update: Wait, I guess it didn't work for me. (Sorry, was rushed.) You can use this:

>perl -le"@a=qw(a b c d e); undef $_ for @a[2,3]; print for @a"
a
b


e
[download]

The docs are quite specific as to what undef accepts for args. I would expect a built-in to complain if you gave it incorrect arguments, but that's what you are doing.

By the way, undef @h{@k}; is not allowed and doesn't work either.

$ perl -le"%h=map { $_=>$_ } qw(a b c d e); undef @h{qw( c d )}; print
+ qq{$_: $h{$_}} for sort keys %h"
a: a
b: b
c: c
d:
e: e
[download]