 |  |
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
|  | |
| 15.5. Changing Text Color |  | 15.7. Ringing the Terminal Bell |
Copyright © 2003 O'Reilly & Associates. All rights reserved.