while (<FH>) {
...
}
[download]

while (defined ($_ = <FH>)) {
...
}
[download]

while (($_ = <STDIN>) ne "\n"){
...
}
[download]

Or alternatively...

while (<STDIN>) {
  last if $_ eq "\n";
}
[download]

In the first place, eq is the string equality operator (!= is numeric). In the second place, the result of <STDIN> won't be automatically assigned to $_ because it is part of a more complex expressions (see "IO Operators" in perlop).

"but I can't test directly against the <FOO>"

I think there is one thing has not been quite straightened yet. In fact, you can test directly against <STDIN>, and that is absolutely not a problem. Let's fix the != problem others pointed out, and test with this code:

use strict;
use warnings;

while (<STDIN> ne "quit\n") {
    print ;#I intentionally leave this here, and you will see "Use of 
+uninitialized value in print at foo.pl line 5, <STDIN> line blah."
}
[download]

As others pointed out, $_ does not contain what you entered, but I intentionally leave it as is.

The real point I want to make here is that, this piece of demo code does quit the while loop when you enter "quit\n", but does not quit on other input.

The code itself is not much useful, as $_ does not contain what you entered, and you don't have other variable does that. But I do want to have one fact corrected: you can test against <STDIN>.

update: As suggested, if there is more processing to come it could be
while (defined($_ = <>)) { last if /^$/;print}

exit? I think that last is the appropriate construct here...


Who is Kayser Söze?
Code is (almost) always untested.

The intent is to print every line entered at the console until a blank line is entered.

so, you could exit isn't it ?
or you could decide to continue with something else to do and in that case , you're right a last is better suited, but that was not the purpose. my code was from a one-liner test

perl -pe '/^$/ && exit'
[download]

which produce the expexted result and become

perl -MO=Deparse -pe '/^$/ && exit'
[download]

before I post it :-)
--
dominix

exit is not a good idea, last is a much better idea. exit will stop the execution of the script, last will stop the loop, see the difference in: perl -wle 'print q(X);while(1) { exit; } print q(Y);' and perl -wle 'print q(X);while(1) { last; } print q(Y);'

See perlvar for $/, and perlipc for why.