Thanks for your replay , but ...

#!/perl/bin/perl -w
use strict;
my $string = "Hello $ World \n";
$string  =~ tr/A-Za-z0-9.-_//cd;
print $string;

###
### prints out 
Global symbol "$World" requires explicit package name
[download]

same for the other example

and i have one more question how can i add a space

to s/// in the example you gave to me ?

leaving a space at the end or adding \s giving me errors