Input from the keyboard in command line application

Question

I am attempting to get the keyboard input for a command line app for the new Apple programming language Swift   I ve scanned the docs to no avail   import Foundation  println  What is your name          Any ideas

User · Answer

Another alternative is to link libedit for proper line editing (arrow keys, etc.) and optional history support. I wanted this for a project I'm starting and put together a basic example for how I set it up.

Usage from swift

let prompt: Prompt = Prompt(argv0: C_ARGV[0])

while (true) {
    if let line = prompt.gets() {
        print("You typed \(line)")
    }
}

ObjC wrapper to expose libedit

#import <histedit.h>

char* prompt(EditLine *e) {
    return "> ";
}

@implementation Prompt

EditLine* _el;
History* _hist;
HistEvent _ev;

- (instancetype) initWithArgv0:(const char*)argv0 {
    if (self = [super init]) {
        // Setup the editor
        _el = el_init(argv0, stdin, stdout, stderr);
        el_set(_el, EL_PROMPT, &prompt);
        el_set(_el, EL_EDITOR, "emacs");

        // With support for history
        _hist = history_init();
        history(_hist, &_ev, H_SETSIZE, 800);
        el_set(_el, EL_HIST, history, _hist);
    }

    return self;
}

- (void) dealloc {
    if (_hist != NULL) {
        history_end(_hist);
        _hist = NULL;
    }

    if (_el != NULL) {
        el_end(_el);
        _el = NULL;
    }
}

- (NSString*) gets {

    // line includes the trailing newline
    int count;
    const char* line = el_gets(_el, &count);

    if (count > 0) {
        history(_hist, &_ev, H_ENTER, line);

        return [NSString stringWithCString:line encoding:NSUTF8StringEncoding];
    }

    return nil;
}

@end

User · Answer

The top ranked answer to this question suggests using the readLine   method to take in user input from the command line  However  I want to note that you need to use the   operator when calling this method to return a string instead of an optional   var response   readLine

User · Answer

I swear to God   the solution to this utterly basic problem  eluded me for YEARS  It s SO simple   but there is so much vague   bad information out there  hopefully I can save someone from some of the bottomless rabbit holes that I ended up in     So then  lets s get a  string  from  the user  via  the console   via stdin  shall we    NSString alloc initWithData   NSFileHandle fileHandleWithStandardInput availableData                            encoding NSUTF8StringEncoding     if you want it WITHOUT the trailing newline  just add           stringByTrimmingCharactersInSet                         NSCharacterSet newlineCharacterSet     Ta Da       e

User · Answer

Before                          Correction

User · Answer

If you want to read space separated string  and immediately split the string into an array  you can do this   var arr   readLine    characters split      map String init   eg   print  What is your full name     var arr   readLine    characters split      map String init   var firstName      var middleName      var lastName       if arr count  gt  0       firstName   arr 0    if arr count  gt  2       middleName   arr 1      lastName   arr 2    else if arr count  gt  1       lastName   arr 1     print  First Name    firstName    print  Middle Name    middleName    print  Last Name    lastName

User · Answer

Since there were no fancy solutions to this problem  I made a tiny class to read and parse the standard input in Swift  You can find it here   Example  To parse    42 st ring  -0 987654321 12345678900  42   You do   let stdin   StreamScanner standardInput  if     let i  Int   stdin read        let s  String   stdin read        let d  Double   stdin read        let i64  Int64   stdin read        let f  Float   stdin read         print    i    s    d    i64    f       prints  42 st ring  -0 987654321 12345678900 0 42

User · Answer

Swift 5   If you continuously want input from keyboard   without ending the program  like a stream of input  Use below steps    Create new project of type comnnad line tool    Add below code in main swift file   var inputArray    String     while let input   readLine      guard input     quit  else    break     inputArray append input   print  You entered    input     print inputArray   print  Enter a word          RunThe project and click the executable under Products folder in Xcode and open in finder Double click the executable to open it  Now enter your Inputs  Terminal will look something like this

User · Answer

I just wanted to comment  I have not enough reps  on xenadu s implementation  because CChar in OS X is Int8  and Swift does not like at all when you add to the array when getchar   returns parts of UTF-8  or anything else above 7 bit   I am using an array of UInt8 instead  and it works great and String fromCString converts the UInt8 into UTF-8 just fine    However this is how I done it  func readln   - gt   str  String   hadError  Bool        var cstr   UInt8           var c  Int32   0     while c    EOF           c   getchar           if  c    10    c    13     c  gt  255   break           cstr append UInt8 c             cstr append 0      return String fromCStringRepairingIllFormedUTF8 UnsafePointer lt CChar gt  cstr      while true       if let mystring   readln   str           println    gt    mystring

User · Answer

It s actually not that easy  you have to interact with the C API  There is no alternative to scanf  I ve build a little example   main swift  import Foundation  var output  CInt   0 getInput  amp output   println output     UserInput c   include  lt stdio h gt   void getInput int  output        scanf   i   output        cliinput-Bridging-Header h  void getInput int  output

User · Answer

I managed to figure it out without dropping down in to C   My solution is as follows   func input   - gt  String       var keyboard   NSFileHandle fileHandleWithStandardInput       var inputData   keyboard availableData     return NSString data  inputData  encoding NSUTF8StringEncoding       More recent versions of Xcode need an explicit typecast  works in Xcode 6 4    func input   - gt  String       var keyboard   NSFileHandle fileHandleWithStandardInput       var inputData   keyboard availableData     return NSString data  inputData  encoding NSUTF8StringEncoding   as String

User · Answer

This works in xCode v6 2  I think that s Swift v1 2  func input   - gt  String       var keyboard   NSFileHandle fileHandleWithStandardInput       var inputData   keyboard availableData     return NSString data  inputData  encoding NSUTF8StringEncoding   as String

User · Answer

I have now been able to get Keyboard input in Swift by using the following   In my main swift file I declared a variable i and assigned to it the function GetInt   which I defined in Objective C  Through  a so called Bridging Header where I declared the function prototype for GetInt I could link to main swift  Here are the files   main swift   var i  CInt   GetInt   println  Your input is   i        Bridging Header    include  obj m   int GetInt      obj m    import  lt Foundation Foundation h gt   import  lt stdio h gt   import  lt stdlib h gt   int GetInt         int i      scanf   i    amp i       return i      In obj m it is possible to include the c standard output and input  stdio h  as well as the c standard library stdlib h which enables you to program in C in Objective-C  which means there is no need for including a real swift file like user c or something like that   Hope I could help   Edit  It is not possible to get String input through C because here I am using the CInt -  the integer type of C and not of Swift  There is no equivalent Swift type for the C char   Therefore String is not convertible to string  But there are fairly enough solutions around here to get String input   Raul

User · Answer

var a  scanf  quot  s n quot   n    I tested this out in ObjC  and maybe this will be useful

User · Answer

In general readLine   function is used for scanning input from console  But it will not work in normal iOS project until or unless you add  command-line tool    The best way for testing  you can do     1  Create an macOS file    2  Use the readLine   func to scan optional String from console   import Foundation   print  Please enter some input n     if let response   readLine         print  output    response     else       print  Nothing        Output    Please enter some input  Hello  World output   Hello  World Program ended with exit code  0

User · Answer

import Foundation print  quot Enter a number quot   let number   Int   Int readLine strippingNewline  true       0 if number  lt  5        print  quot Small quot    else      print  quot Big quot     for i in 0   number      print i

User · Answer

Here is simple example of taking input from user on console based application   You can use readLine    Take input from console for first number then press enter  After that take input for second number as shown in the image below   func solveMefirst firstNo  Int   secondNo  Int  - gt  Int       return firstNo   secondNo    let num1   readLine   let num2   readLine    var IntNum1   Int num1   var IntNum2   Int num2    let sum   solveMefirst IntNum1   secondNo  IntNum2   print sum

User · Answer

edit As of Swift 2 2 the standard library includes readLine  I ll also note Swift switched to markdown doc comments  Leaving my original answer for historical context    Just for completeness  here is a Swift implementation of readln I ve been using  It has an optional parameter to indicate the maximum number of bytes you want to read  which may or may not be the length of the String    This also demonstrates the proper use of swiftdoc comments - Swift will generate a  lt project gt  swiftdoc file and Xcode will use it      reads a line from standard input         param  max specifies the number of bytes to read         returns  the string  or nil if an error was encountered trying to read Stdin public func readln max Int   8192  - gt  String        assert max  gt  0   max must be between 1 and Int max        var buf Array lt CChar gt           var c   getchar       while c    EOF  amp  amp  c    10  amp  amp  buf count  lt  max           buf append CChar c           c   getchar                always null terminate     buf append CChar 0        return buf withUnsafeBufferPointer   String fromCString  0 baseAddress

User · Answer

Lots of outdated answers to this question  As of Swift 2  the Swift Standard Library contains the readline   function  It will return an Optional but it will only be nil if EOF has been reached  which will not happen when getting input from the keyboard so it can safely be unwrapped by force in those scenarios  If the user does not enter anything its  unwrapped  value will be an empty string  Here s a small utility function that uses recursion to prompt the user until at least one character has been entered   func prompt message  String  - gt  String       print message      let input  String   readLine        if input                 return prompt message  message        else           return input          let input   prompt message   Enter something    print  You entered   input      Note that using optional binding  if let input   readLine    to check if something was entered as proposed in other answers will not have the desired effect  as it will never be nil and at least    when accepting keyboard input   This will not work in a Playground or any other environment where you does not have access to the command prompt  It seems to have issues in the command-line REPL as well

User · Answer

The correct way to do this is to use readLine  from the Swift Standard Library   Example   let response   readLine     Will give you an Optional value containing the entered text

User · Answer

When readLine   function is run on Xcode  the debug console waits for input  The rest of the code will be resumed after input is done        let inputStr   readLine       if let inputStr   inputStr           print inputStr

[swift] Input from the keyboard in command line application

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