Capturing control characters

aztlan667 has asked for the wisdom of the Perl Monks concerning the following question:

Greetings, I am trying to create a script that will read in a series of characters and look for a certain sequence of characters. I am having a hard time reading in control characters like <CTRL> and <ALT>. I'm basically am trying to create a keylogger that will look for a sequence like "<CTRL>+<ALT>+B" and execute another script when that happens. I've tried using the following code:

my $key_buf;
my $sequence = qr/some_keys/g;

system "stty cbreak < /dev/tty > /dev/tty 2>&1";
while (($key=getc) ) {
                                                            
    $key_buf .= $key;
    if ($key_buf =~ $my_sequence) {
        system "xmessage 'OH YA!'";
        last;
    }
    last if $key eq "q";
}

system "stty -cbreak < /dev/tty > /dev/tty 2>&1";
[download]

I've also tried using Term::ReadKey and Term::InKey, but I've had no success in capturing the control characters. Any suggestions or anything I'm missing?

Thank you.

Comment on Capturing control characters Download Code

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Re: Capturing control characters by almut (Canon) on Feb 10, 2009 at 02:59 UTC
The general problem here is that modifier keys like <CTRL> and <ALT> are being interpreted by the tty itself. You could try something like this, however: `#!/usr/bin/perl use Term::ReadKey; my $my_sequence = qr/\x1b\x02\z/; # <CTRL>+<ALT>+B my $key; my $key_buf; ReadMode 4; while ($key ne 'q') { $key = ReadKey(); printf "key=\\x%02x\n", ord($key); # debug $key_buf .= $key; if ($key_buf =~ $my_sequence) { system "xmessage 'OH YA!'"; last; } }; ReadMode 0;` [download] This has its limits, too (for example I wouldn't know how to tell apart `<CTRL>+<ALT>+B` from `<CTRL>+<ALT>+<SHIFT>+B`), but maybe it's sufficient for your purpose. `<CTRL>+A` .. `<CTRL>+Z` typically maps to 1..26 (`ord($key)`, that is); and `<ALT>+...` typically generates a two-byte sequence with a leading ESC (27 or \x1b). Other keys (cursor keys, etc.) generate three-byte sequences... Printing out the sequence you get when you hit a certain key/modifier combination will tell you which substring to match (you don't necessarily need a regex for this, btw; `index()` would do). But in case portability is an issue, be aware that terminals sometimes differ with respect to the sequences they generate — in particular the multi-byte ones... Update: the loop exit condition (`$key eq 'q'`) is probably too simple for production use (it would also exit on hitting `<ALT>+q`, for example, due to the second byte of the escape sequence being `'q'`)... Fixing this is left as an exercise for the reader :)	[reply] [d/l] [select]
Re: Capturing control characters by Joost (Canon) on Feb 10, 2009 at 00:00 UTC
system doesn't work like that. You may want to use IPC::Open3 instead, but note that not every program will cooperate with it, and keylogging is not something many people here will be interested in sharing info about. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply]
Re^2: Capturing control characters by aztlan667 (Novice) on Feb 10, 2009 at 00:52 UTC
I'll tak a look at IPC::Open3. I agree with the sentiment towards keylogging. This isn't a keylogger, per se. It's just a script that will execute some code once a certain key combination has been entered. The end users are fully aware of its presence, and its pretty much the whole reason for using the system.	[reply]