FAQ 5.31 How can I read a single character from a file? From the keyboard?

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From: PerlFAQ Server on 15 Jun 2010 00:00

---

This is an excerpt from the latest version perlfaq5.pod, which
comes with the standard Perl distribution. These postings aim to
reduce the number of repeated questions as well as allow the community
to review and update the answers. The latest version of the complete
perlfaq is at http://faq.perl.org .

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5.31: How can I read a single character from a file? From the keyboard?

You can use the builtin "getc()" function for most filehandles, but it
won't (easily) work on a terminal device. For STDIN, either use the
Term::ReadKey module from CPAN or use the sample code in "getc" in
perlfunc.

If your system supports the portable operating system programming
interface (POSIX), you can use the following code, which you'll note
turns off echo processing as well.

#!/usr/bin/perl -w
use strict;
$| = 1;
for (1..4) {
print "gimme: ";
my $got = getone();
print "--> $got\n";
}
exit;

BEGIN {
use POSIX qw(:termios_h);

my ($term, $oterm, $echo, $noecho, $fd_stdin);

my $fd_stdin = fileno(STDIN);

$term = POSIX::Termios->new();
$term->getattr($fd_stdin);
$oterm = $term->getlflag();

$echo = ECHO | ECHOK | ICANON;
$noecho = $oterm & ~$echo;

sub cbreak {
$term->setlflag($noecho);
$term->setcc(VTIME, 1);
$term->setattr($fd_stdin, TCSANOW);
}

sub cooked {
$term->setlflag($oterm);
$term->setcc(VTIME, 0);
$term->setattr($fd_stdin, TCSANOW);
}

sub getone {
my $key = '';
cbreak();
sysread(STDIN, $key, 1);
cooked();
return $key;
}

}

END { cooked() }

The Term::ReadKey module from CPAN may be easier to use. Recent versions
include also support for non-portable systems as well.

use Term::ReadKey;
open my $tty, '<', '/dev/tty';
print "Gimme a char: ";
ReadMode "raw";
my $key = ReadKey 0, $tty;
ReadMode "normal";
printf "\nYou said %s, char number %03d\n",
$key, ord $key;



--------------------------------------------------------------------

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are not necessarily experts in every domain where Perl might show up,
so please include as much information as possible and relevant in any
corrections. The perlfaq-workers also don't have access to every
operating system or platform, so please include relevant details for
corrections to examples that do not work on particular platforms.
Working code is greatly appreciated.

If you'd like to help maintain the perlfaq, see the details in
perlfaq.pod.

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