4.10. Terminal capability probes

The TTY module answers whether a stream is attached to a real terminal, and how wide that terminal is.

This is the gate for anything that redraws itself with a carriage return: a progress bar written to a pipe, a redirect, or a supervising process is garbage in the resulting log. Checking TERM is not a substitute — it stays set when standard output is redirected. daslib/ansi_colors handles styling; this module answers the capability question underneath it.

All functions and symbols are in “tty” module, use require to get access to it.

require daslib/tty

Example:

require daslib/tty

[export]
def main() {
    if (is_stdout_terminal()) {
        print("drawing a {terminal_columns()}-column progress bar\n")
    } else {
        print("output is captured — emitting plain lines instead\n")
    }
}

4.10.1. Constants

TTY_STDIN = 0

TTY_STDIN:int const

TTY_STDOUT = 1

TTY_STDOUT:int const

TTY_STDERR = 2

TTY_STDERR:int const

TTY_DEFAULT_WIDTH = 80

TTY_DEFAULT_WIDTH:int const

4.10.2. Terminal detection

• is_stderr_terminal () : bool

• is_stdin_terminal () : bool

• is_stdout_terminal () : bool

• is_stream_terminal (fd: int) : bool

is_stderr_terminal(): bool

True when standard error is attached to a terminal.

is_stdin_terminal(): bool

True when standard input is attached to a terminal.

is_stdout_terminal(): bool

True when standard output is attached to a terminal. This is the gate for a redrawn progress display — false under a pipe, a redirect, or a supervising process.

is_stream_terminal(fd: int ): bool

True when the standard stream fd (TTY_STDIN / TTY_STDOUT / TTY_STDERR) is attached to a terminal. Any other descriptor is false.

Arguments:

• fd : int

4.10.3. Terminal geometry

• terminal_columns (fallback: int = TTY_DEFAULT_WIDTH) : int

terminal_columns(fallback: int = TTY_DEFAULT_WIDTH ): int

def terminal_columns (fallback: int = TTY_DEFAULT_WIDTH) : int

Arguments:

• fallback : int