If you're on a POSIXy system you can read user input from /dev/tty:

open T,"<","/dev/tty" or die "Can't read from /dev/tty: $!";
print "What do you want to do with this message?";

my $response = <T>;
print $response;
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Ah hah! I just did this.

close(STDIN);
open(STDIN,"<","/dev/tty") or die "Can't reopen STDIN from /dev/tty: $
+!";
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I don't know if it's any better or worse than using a new filehandle, but it keeps me happy.

BTW: What would I do on a non-posix system?

I don't know if it's any better or worse than using a new filehandle, but it keeps me happy.

It's exactly as the same IMHO and in both ways it keeps me unhappy: I find your way to do what you want to do clumsy and error prone, which is probably the reason why I couldn't understand your question at all, first.

BTW: What would I do on a non-posix system?

But seriously, why don't you use <>'s magic instead?

q:~/tmp [22:37:14]$ cat headybrew.pl
#!/usr/bin/perl

chomp(my @msg =<>);
print @msg, "\n";

print "What do you want to do with this message?";

$response = <STDIN>;
print $response;

q:~/tmp [22:37:17]$ ./headybrew.pl 'ls|'
headybrew.plheadybrew.pl~
What do you want to do with this message?foo
foo
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Thanks.

Sounds like that would work, but isn't there a way to just switch my STDIN back to the keyboard?

Sounds like that would work, but isn't there a way to just switch my STDIN back to the keyboard?

Nope, because it's not been switched forth. It has been switched away once and for all out of your program. Of course you can reopen STDIN to whatever you want, if you like:

q:~/tmp [22:27:50]$ cat headybrew.pl
#!/usr/bin/perl

chomp(my @msg =<>);
print @msg, "\n";

print "What do you want to do with this message?";

close STDIN;
open STDIN, '<', '/dev/tty' or die "Can't read from /dev/tty: $!\n";
my $response = <STDIN>;
print $response;

q:~/tmp [22:27:58]$ ls | ./headybrew.pl
headybrew.plheadybrew.pl~
What do you want to do with this message?foo
foo
q:~/tmp [22:28:08]$
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But then you rely on something hardcoded that you know or want to be the keyboard. Because from within your program you have no notion of "what" the keyboard would have been, had STDIN not been redirected by the shell.

#!/usr/bin/perl

die("usage: sillytest file [file [file [...]]]\n")
   if not @ARGV;

my @msg = <>;
chomp(@msg);
print(join("\n", @msg));
print "What do you want to do with this message?";
my $response = <STDIN>;
print $response;
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To pass the output of ls, you'd do
sillytest `ls`
or just
sillytest *

By the way, you might be interested in
my $msg = do { local $/; <> }; print($msg);

Term::UI (on CPAN) looks okay, too.

It receives and prints the @msg lines properly, but then how do I get it to get input from the keyboard again after I'm done reading from the diamond operator?

You just get it:

Windows:

C:\temp>headybrew.pl
foo
bar
baz
^Z
foo
bar
bazWhat do you want to do with this message?wtf
wtf
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*NIX:

wolfgang:~ [21:40:12]$ ./headybrew.pl
foo
bar
baz
foo
bar
bazWhat do you want to do with this message?wtf
wtf
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You just have to pass an end of file to interrupt the first sequence, which happens to be ^Z in the former environment and ^D in the latter. Or did you mean anything else?

Update: apologies, hadn't noticed the $ ls | sillytest, my fault, but perhaps you may have put that in <code> tags too, for maximum visibility.

Yeah, but I can't pass and EOF or anything else in. I'm at the mercy of what get's passed in from some other program's output.

It does work. It just doesn't do what you expect because you don't understand filehandles properly :-)

STDIN is just another filehandle. Normally it is opened to whatever device is attached to your console. But because you are piping another program's output into your program's input, your program's STDIN is instead attached to the other program's STDOUT. It will remain attached to that until you tell it otherwise.

You might find this tutorial useful, in particular the few pages starting here.

 
$ ls | xargs sillytest
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#!/usr/bin/perl

my @msg = join "\n", @ARGV;
# continue normally - STDIN was not redirected by xargs
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#!/usr/bin/perl
# XARGS.EXE v0.1

shift @ARGV;
push @ARGV, <STDIN>;
chomp @ARGV;
exec join( ' '. @ARGV;
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use the sleep <int> function instead.

#!/usr/bin/perl

my @msg = (<>); chomp(@msg);

print join("\n",@msg),"\n";

print STDOUT  "What do you want to do with this message?\n";$|++;
sleep (5);
my $response = <STDIN>;
print $response;$|++;
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All that does is cause the program to wait 5 seconds before exiting. It still doesn't receive any input from the keyboard (because, as others have pointed out above, STDIN isn't connected to the keyboard).

And <code> tags are your friends.