perl function ioctl

The ioctl function in Perl is used to perform low-level I/O control operations on filehandles. It takes three arguments: a filehandle, a request code, and a scalar value that contains input and/or output data for the operation.

Here's an example that demonstrates how to use ioctl:

#!/usr/bin/perl

use strict;
use warnings;

# Open a file
open my $fh, "<", "/dev/tty" or die "Can't open /dev/tty: $!";

# Set the terminal to raw mode
my $termios = `stty -g`;
system "stty raw -echo </dev/tty";

# Read a single character from the terminal
my $char;
ioctl $fh, 0x40067408, $char;

# Restore the terminal to its previous mode
system "stty $termios </dev/tty";

In this example, we start by opening the file /dev/tty for reading. We then use the system function to run the stty command to set the terminal to raw mode, which disables line buffering and input processing. We save the previous terminal settings to a variable called $termios.

We then use the ioctl function to read a single character from the terminal. The request code 0x40067408 is a constant that represents the TIOCSTI operation, which allows a single character to be pushed back onto the input queue of the terminal driver. We pass the $char variable as the input data for the operation, which will be set to the character that the user types.

Finally, we use system again to restore the terminal to its previous mode using the saved $termios variable.

Note that ioctl is a low-level function that is typically used for specialized operations on certain types of filehandles, such as terminals, sockets, or device files. In general, you should only use ioctl if you have a specific need for low-level I/O control operations. For most file I/O operations, you should use the higher-level functions provided by Perl, such as open, read, and write.