swift2 equivalent of python's shlex.split to preserve the whitespace within quoted strings

Question

I'm looking for an existing swift2 function to split string input on whitespace while at the same time preserving whitespace within quoted strings.

I have read stack overflow question 25678373. My question does not appear to be a duplicate.

I searched for similar functionality in cocoapods. I did not find it.

If this shlex.split function does not exist in swift2, what is an effective alternate way to accomplish something similar? What is an alternate way to split a string while preserving whitespace within internal quoted strings?

Here's an example of what I mean in python:

$    python
Python 2.7.6 (default, Jun 22 2015, 18:00:18) 
[GCC 4.8.2] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import shlex
>>> input=""" alpha 2 'chicken with teeth' 4 'cat with wings' 6 turkey"""
>>> results = shlex.split(input)
>>> type(results)
<type 'list'>
>>> results[0]
'alpha'
>>> results[2]
'chicken with teeth'
>>> for term in results:
...     print(term)
... 
alpha
2
chicken with teeth
4
cat with wings
6
turkey
>>>

`I'm looking for an existing swift2 function to [...]` There is no such function in the Swift standard library. — Eric Aya, Apr 03 '16 at 20:29
BTW, the [source code for shlex.split](http://scons.org/doc/1.3.1/HTML/scons-api/SCons.compat._scons_shlex-pysrc.html) is rather complex, it uses a lexical parser to achieve this task. — Eric Aya, Apr 04 '16 at 10:37

score 2 · Accepted Answer · answered Apr 04 '16 at 10:35

As @EricD writes in his comment to you, there exists no such native Swift function. You can, however, quite readily write your own such split function, e.g.

extension String {

    func shlexSplit() -> [String] {
        /* separate words by spaces */
        var bar = self.componentsSeparatedByString(" ")

        /* identify array idx ranges of quoted (') sets of words */
        var accumulating = false
        var from = 0
        var joinSegments : [(Int, Int)] = []

        for (i,str) in bar.enumerate() {
            if str.containsString("'") {
                if accumulating { joinSegments.append((from, i)) }
                else { from = i }
                accumulating = !accumulating
            }
        }

        /* join matching word ranges with " " */
        for (from, through) in joinSegments.reverse() {
            bar.replaceRange(from...through, 
                with: [bar[from...through].joinWithSeparator(" ")])
        }

        return bar
    }
}

Usage example

/* exampe usage */
let foo = "alpha 2 'chicken with teeth' 4 'cat with wings' 6 turkey"
let bar = foo.shlexSplit()

bar.forEach{ print($0) }
/* alpha
 2
 'chicken with teeth'
 4
 'cat with wings'
 6
 turkey */

Note that the above assumes the input string have matching sets of quote delimiters '.

user3441734 · Answer 2 · 2016-04-04T15:18:33.853

'pure' swift (no Foundation) example

extension String {
    // split by first incidence of character 
    func split(c: Character)->(String,String) {
        var head: String = "", tail: String = ""
        if let i = characters.indexOf(c) {
            let j = startIndex.distanceTo(i)
            head = String(characters.prefix(j))
            tail = String(characters.dropFirst(j + 1))
        } else {
            head = self
        }
        return (head, tail)
    }
}

// what you are looking for

func split(str: String)->[String] {
    // internal state
    var state:((String,String), [String], Bool) = (str.split("'"), [], false)
    repeat {
        if !state.2 {
            // you can define more whitespace characters
            state.1
                .appendContentsOf(state.0.0.characters.split{" \t\n\r".characters.contains($0)}
                    .map(String.init))
            state.2 = true
        } else {
            state.1.append(state.0.0)
            state.2 = false
        }
        state.0 = state.0.1.split("'")
    } while !state.0.0.isEmpty
    return state.1
}

Usage

let str = "a 2  'b   c'   d  ''"
dump(split(str))
/*
 ▿ 4 elements
   - [0]: a
   - [1]: 2
   - [2]: b   c
   - [3]: d
 */

swift2 equivalent of python's shlex.split to preserve the whitespace within quoted strings

2 Answers2