Read single key from stdin

Question

Created Mar ’21

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I want to read a key from the input of the terminal, with readLine I have to press enter first, how do I get around this

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Answer 1

DTS Engineer OP

Apple

Apr ’21

Swift does not have built-in support for this. Rather, you’re expected to use standard BSD constructs for putting the terminal into non-canonical mode. For example, if you build this code:

Code Block  import Foundation
func main() {
    let fd = STDIN_FILENO
    guard isatty(fd) != 0 else { fatalError() }
    var tio = termios()
    var ok = tcgetattr(fd, &tio) >= 0
    guard ok else { fatalError() }
    tio.c_lflag &= ~UInt(ICANON | ECHO)
    ok = tcsetattr(fd, TCSANOW, &tio) >= 0
    guard ok else { fatalError() }
    while true {
        var buf: UInt8 = 0
        let readResult = read(fd, &buf, 1)
        if readResult < 0 {
            fatalError()
        } else if readResult == 0 {
            exit(EXIT_SUCCESS)
        } else {
            assert(readResult == 1)
            print(buf)
        }
    }
}
main()

and then run it from Terminal and then type some characters, you’ll see output like this:

Code Block  % ./NonCanonTest
104
101
108
108
111
32
99
114
117
101
108
32
119
111
114
108
100

For more info on this, see the termios man page.

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Quinn “The Eskimo!” @ Developer Technical Support @ Apple
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