Thanks for all your answers, but it seems i am missing something.
if i write

my $t;
sub show { print eval "\$$_" for @_; }
sub init { $t = 'test'; show(qw( t )); }

=> nothing
[download]

but if i write

my $t;
sub show { print $t; print eval "\$$_" for @_; }
sub init { $t = 'test'; show(qw( t )); }

=> testtest
[download]

So it seems eval can not find $t in the right scope but if i use $t in a usual way before calling eval, it can find it...