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About terminal : Read-screen-character-from-terminal

Question Detail

As far I researched, terminfo/termcap and ioctl don’t allow to query character at (x,y) position on terminal’s screen. This is rather unexpected, because:

  • one can read e.g. screen dimensions from terminal (e.g. tput co, tput li),
  • one can read input from terminal

– the two mean that communication with terminal is bidirectional. Is there really no way to query a character at given position, like with *inch*, *in_wch* curses functions (which work only for curses windows)?

Question Answer

That’s expected (not “unexpected”):

  • tput gives values from a combination of the terminal database (fixed) and the operating system (changeable), but does not ask the terminal.
  • reading from the terminal is by an input stream from the device (what terminals are designed to do).

Some (not all) terminals support an escape sequence which asks the terminal where the cursor is. The resize program uses that to obtain the screensize. But keep in mind that it is known to be terminal-dependent, as mentioned in the manual page:

-s [rows columns]
This option indicates that Sun console escape sequences will be
used instead of the VT100-style xterm escape codes.

Very few terminals support an escape sequence which will simply read characters from the screen. Not everyone likes the notion of a program that can read their screen — perhaps without their knowledge.

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