Ascii value is different

[nagalenoj]

When I use the perl package Term::Screen and gets some input from user, newline's ASCII value is returning as 13. And, when I comment the use of Term::Screen, the ASCII value is returning as 10.

How does it got change?

use Term::ReadKey;
# use Term::Screen;

# my $scr;
# $scr = Term::Screen->new;
# unless ($scr) { die "Couldn't create object for Term::Screen\n"; }
# $scr->clrscr;

# Get the user name and password
my ($user, $key);
print "\nYour name: ";

ReadMode 4; # Turn off controls keys
while (1)  {
    $key = ReadKey(0);
    if (ord($key) == 13)  {
        print "Newline got at 13";
        last;
    }
    if (ord($key) == 10)  {
        print "Newline got at 10";
        last;
    }
    print $key, "--", ord($key),"\n";
}
print $key, "--", ord($key),"\n";
ReadMode 0; # Reset tty mode before exiting

[almut]

Term::Screen calls stty raw -echo under the hood, which unsets the tty feature "translate carriage return to newline" (icrnl) — i.e. "raw" means (among other things) -icrnl.

Not sure if there are better ways... but a quick hack might be to patch Term::Screen to issue stty raw -echo icrnl instead, or maybe call stty icrnl yourself from your script after having used Term::Screen  (haven't tested it for side effects, though).

Your script with Term::Screen commented (just for demo):

$ stty -icrnl
$ ./835470.pl

Your name: a--97
b--98
--13ine got at 13

$ stty icrnl
$ ./835470.pl

Your name: a--97
b--98
Newline got at 10
--10

[cdarke]

UNIX terminals can run in canonical ('cooked') or non-canonical ('raw') mode. The difference is that in canonical mode certain characters are converted, for example Ctrl+c generates (by default) a SIGINT and <Return> gets translated to a new-line (crtonl).

The documentation for Term::Screen clearly states that it runs in raw mode, which means there is no conversion. ASCII character 13 is a CR, the code for the return key, in canonical mode this gets translated to 10, which is LF (a line feed).


Term::ReadKey has a ReadMode function which you could use to get consistent results.
See also, on the shell command-line, stty -a