Support paths relative to the user’s home directory

This patch fixes a bug that would cause shelling out at a path containing
a tilde to fail. The reason was that ShellOut was wrapping all paths in
quotes, in order to escape spaces. With this, spaces are properly escaped
instead.

Sources/ShellOut.swift

@@ -31,7 +31,7 @@ import Foundation
                                         outputHandle: FileHandle? = nil,
                                         errorHandle: FileHandle? = nil) throws -> String {
     let process = Process()
-    let command = "cd \"\(path)\" && \(command) \(arguments.joined(separator: " "))"
+    let command = "cd \(path.escapingSpaces) && \(command) \(arguments.joined(separator: " "))"
     return try process.launchBash(with: command, outputHandle: outputHandle, errorHandle: errorHandle)
 }
 
@@ -418,6 +418,10 @@ private extension Data {
 }
 
 private extension String {
+    var escapingSpaces: String {
+        return replacingOccurrences(of: " ", with: "\\ ")
+    }
+
     func appending(argument: String) -> String {
         return "\(self) \"\(argument)\""
     }

Tests/ShellOutTests/ShellOutTests.swift

@@ -32,6 +32,19 @@ class ShellOutTests: XCTestCase {
         XCTAssertEqual(textFileContent, "Hello")
     }
 
+    func testSingleCommandAtPathContainingSpace() throws {
+        try shellOut(to: "mkdir -p \"ShellOut Test Folder\"", at: NSTemporaryDirectory())
+        try shellOut(to: "echo \"Hello\" > File", at: NSTemporaryDirectory() + "ShellOut Test Folder")
+
+        let output = try shellOut(to: "cat \(NSTemporaryDirectory())ShellOut\\ Test\\ Folder/File")
+        XCTAssertEqual(output, "Hello")
+    }
+
+    func testSingleCommandAtPathContainingTilde() throws {
+        let homeContents = try shellOut(to: "ls", at: "~")
+        XCTAssertFalse(homeContents.isEmpty)
+    }
+
     func testSeriesOfCommands() throws {
         let echo = try shellOut(to: ["echo \"Hello\"", "echo \"world\""])
         XCTAssertEqual(echo, "Hello\nworld")