sub prompt ($;$) {  ## no critic
    my($mess, $def) = @_;
    Carp::confess("prompt function called without an argument") 
        unless defined $mess;

    my $isa_tty = -t STDIN && (-t STDOUT || !(-f STDOUT || -c STDOUT))
+ ;

    my $dispdef = defined $def ? "[$def] " : " ";
    $def = defined $def ? $def : "";

    local $|=1;
    local $\;
    print "$mess $dispdef";

    my $ans;
    if ($ENV{PERL_MM_USE_DEFAULT} || (!$isa_tty && eof STDIN)) {
        print "$def\n";
    }
    else {
        $ans = <STDIN>;
        if( defined $ans ) {
            chomp $ans;
        }
        else { # user hit ctrl-D
            print "\n";
        }
    }

    return (!defined $ans || $ans eq '') ? $def : $ans;
}
[download]

perl -e"warn scalar readline(STDIN)"
perl5.8.7 -e"warn scalar readline(STDIN)"
[download]