$ perl 947860.pl
Global symbol "$letter" requires explicit package name at 947860.pl line 5.
Global symbol "$letter" requires explicit package name at 947860.pl line 8.
Global symbol "$letter" requires explicit package name at 947860.pl line 10.
Execution of 947860.pl aborted due to compilation errors (#1)
    (F) You've said "use strict" or "use strict vars", which indicates
    that all variables must either be lexically scoped (using "my" or "state"),
    declared beforehand using "our", or explicitly qualified to say
    which package the global variable is in (using "::").

BEGIN not safe after errors--compilation aborted at /usr/lib/perl5/5.10/Carp/Heavy.pm line 11.
Compilation failed in require at /usr/lib/perl5/5.10/Carp.pm line 33.