Linux: Unbuffered reading from stdin

Hi folks.

I'm somewhat new to *nix programming and just ran into a problem. I have
to take user input from the terminal but like to constrain that to some
rules given, i.e. "numbers only" or "alphanumeric only" etc.
scanf would do, but I don't like the fact that wrong ('disallowed')
characters are visible and all that stuff. For that I need unbuffered
input. Since there seems to be no atomic function to do that I tried to
fiddle around with ioctl() and that seems to work fine. Currently I flag
out ICANON and ECHO from the tty descriptor, set a minimum input of 1
byte, getch() or read() a byte, check, printf(), fine.
However things become nasty when the user presses an key that sends an
escape sequence. I've seen some code on the web that does the following
approach: Check for character==27. If so, read() 4 bytes into a buffer,
zero terminate the buffer accordingly then strcmp() the buffer against
the actual escape sequences.

But then there are two problems:

1) The escape sequences seem to change with every terminal type. On my
terminal the codes for F1 to F5 are ^OP, ^OQ, ^OR, ^OS, ^[15~ (etc)
while on the code given in the web they used to be [[A, [[B etc.
Are there some defines?

2) What happens when the user presses just ESC? Sounds easy to me, just
check if there are no more chars in stdin - but how do you do that? By
just read()ing STDIN_FILENO after an ESC the terminal is blocked until
another key is pressed - that is not really what I want.

Any ideas? Or am I reinventing the wheel?
Regards,
Markus
.

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