A foreach loop does implicitly localize $_ (or whatever variable is
being used as the loop variable), but $_ is not automatically
localized for while(<>) loops. Here is the relevant
entry from the perlop manpage:
Ordinarily you must assign the returned value to a vari-
able, but there is one situation where an automatic
assignment happens. If and only if the input symbol is
the only thing inside the conditional of a `while' state-
ment (even if disguised as a `for(;;)' loop), the value is
automatically assigned to the global variable $_, destroy-
ing whatever was there previously. (This may seem like an
odd thing to you, but you'll use the construct in almost
every Perl script you write.) The $_ variables is not
implicitly localized. You'll have to put a `local $_;'
before the loop if you want that to happen.
However, that last line is
misleading: you'll need to wrap it all in a block, or localize $_ in
the while condition to get the proper effect:
{
local $_;
while(<>){
print;
}
}
# or,
while(local $_ = <>) {
print;
}