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15.6. Reading Single Characters from the Keyboard
15.6.1. Problem
You want to read a single character from
the keyboard. For instance, you've displayed a menu of one-character
options, and you don't want to require users to press the Enter key
to make their selection.
15.6.2. Solution
Use the CPAN module Term::ReadKey to put the terminal into
cbreak mode, read characters from
STDIN, and then put the terminal back into its
normal mode: use Term::ReadKey;
ReadMode 'cbreak';
$key = ReadKey(0);
ReadMode 'normal';
15.6.3. Discussion
Term::ReadKey can put the terminal into many
modes—cbreak is just one of them.
cbreak mode makes each character available to your
program as it is typed (see Example 15-1). It also
echoes the characters to the screen; see Recipe 15.10 for an example of a mode that does not echo.
Example 15-1. sascii
#!/usr/bin/perl -w
# sascii - Show ASCII values for keypresses
use Term::ReadKey;
ReadMode('cbreak');
print "Press keys to see their ASCII values. Use Ctrl-C to quit.\n";
while (1) {
$char = ReadKey(0);
last unless defined $char;
printf(" Decimal: %d\tHex: %x\n", ord($char), ord($char));
}
ReadMode('normal');
Using cbreak mode doesn't prevent the terminal's
device driver from interpreting end-of-file and flow-control
characters. If you want to be able to read a real Ctrl-C (which
normally sends a SIGINT to your process) or a
Ctrl-D (which indicates end-of-file under Unix), you want to use
raw mode.An argument of 0 to ReadKey
indicates that we want a normal read using getc.
If no input is available, the program will pause until there is some.
We can also pass -1 to indicate a non-blocking
read, or a number greater than 0 to indicate the
number of seconds to wait for input to become available; fractional
seconds are allowed. Non-blocking reads and timed-out reads return
either undef when no input is available or a
zero-length string on end-of-file.Recent versions of Term::ReadKey also include limited support for
non-Unix systems.
15.6.4. See Also
The getc and sysread functions
in Chapter 29 of Programming Perl, and in
perlfunc(1); the documentation for the
Term::ReadKey module from CPAN; Recipe 15.8;
Recipe 15.9
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| 15.5. Changing Text Color |  | 15.7. Ringing the Terminal Bell |
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