Determine viewport size (in characters) from command line app in Swift? - swift

Question

I am building a command line tool in Swift and am wondering if there is any way to determine the current width of the viewport while running the app, in order to limit the text on screen to what will fit without wrapping.
I know this is possible in a "real" command line app, since things like pico, man, pine, etc. all render their textual interfaces based on the window size, but I can't seem to find any info on how they do it.
In fact you can even resize the window while they are running and they will refresh. Does anyone know how this works and if it's possible to add support to a command line tool written in Swift?

Answer 1

The C code from Getting terminal width in C? is easily translated to Swift:
import Darwin
var w = winsize()
if ioctl(STDOUT_FILENO, TIOCGWINSZ, &w) == 0 {
print("rows:", w.ws_row, "cols", w.ws_col)
}
(For some reason, this does not work in the Xcode debugger console,
you have to call the executable in the Terminal window.)
Alternatively, using the ncurses library (from Getting terminal width in C?):
import Darwin.ncurses
initscr()
let s = "rows: \(LINES), cols: \(COLS)"
mvaddstr(1, 1, s);
refresh();
getch()
endwin()
To keep track of window resize events you have to handle the
SIGWINCH signal, compare Trapping signals in a Swift command line application:
import Darwin
import Dispatch
var w = winsize()
if ioctl(STDOUT_FILENO, TIOCGWINSZ, &w) == 0 {
print("rows:", w.ws_row, "cols", w.ws_col)
}
let sigwinchSrc = DispatchSource.makeSignalSource(signal: SIGWINCH, queue: .main)
sigwinchSrc.setEventHandler {
if ioctl(STDOUT_FILENO, TIOCGWINSZ, &w) == 0 {
print("rows:", w.ws_row, "cols", w.ws_col)
}
}
sigwinchSrc.resume()
dispatchMain()