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# Swift Command Line Basics

## Running a Swift Script
```bash
swift myscript.swift          # run directly
chmod +x myscript.swift && ./myscript.swift  # make executable (needs shebang)
```

Add this shebang as the first line to run as `./script.swift`:
```swift
#!/usr/bin/swift
```

---

## Printing
```swift
print("Hello, world!")
print("Value:", 42)
print("No newline", terminator: "")   // like echo -n
print("A", "B", "C", separator: ", ") // prints: A, B, C
```

---

## Variables
```swift
var name = "Alice"          // mutable
let age = 30                // constant (like final)
var score: Double = 9.5     // explicit type

name = "Bob"                // ok
// age = 31                 // error - let is immutable
```

Common types: `String`, `Int`, `Double`, `Bool`, `[String]` (array)

---

## String Interpolation
```swift
let city = "Paris"
let pop = 2_100_000
print("City: \(city), population: \(pop)")
print("2 + 2 = \(2 + 2)")
```

---

## Command Line Arguments
```swift
let args = CommandLine.arguments
// args[0] is always the script name

print("Script:", args[0])

if args.count > 1 {
    print("First arg:", args[1])
} else {
    print("No arguments provided")
}

// Loop all args (skip script name)
for arg in args.dropFirst() {
    print("Arg:", arg)
}
```

Run: `swift script.swift foo bar` → args = `["script.swift", "foo", "bar"]`

---

## User Input
```swift
print("Enter your name: ", terminator: "")
if let input = readLine() {
    print("Hello, \(input)!")
}
```

---

## Conditionals
```swift
let x = 10

if x > 5 {
    print("big")
} else if x == 5 {
    print("five")
} else {
    print("small")
}
```

---

## Loops
```swift
// Range loop
for i in 1...5 {
    print(i)
}

// Array loop
let fruits = ["apple", "banana", "cherry"]
for fruit in fruits {
    print(fruit)
}

// While
var count = 0
while count < 3 {
    print(count)
    count += 1
}
```

---

## Functions
```swift
func greet(name: String) -> String {
    return "Hello, \(name)!"
}

print(greet(name: "Alice"))

// No return value
func sayHi() {
    print("Hi!")
}
```

---

## String Operations
```swift
var s = "  Hello, World!  "
s.uppercased()              // "  HELLO, WORLD!  "
s.lowercased()
s.trimmingCharacters(in: .whitespaces)  // "Hello, World!"
s.contains("World")         // true
s.replacingOccurrences(of: "World", with: "Swift")
s.hasPrefix("Hello")
s.hasSuffix("!")
s.split(separator: ",")     // ["  Hello", " World!  "]
```

---

## Running Shell Commands
```swift
import Foundation

func shell(_ cmd: String) -> String {
    let task = Process()
    let pipe = Pipe()
    task.standardOutput = pipe
    task.executableURL = URL(fileURLWithPath: "/bin/bash")
    task.arguments = ["-c", cmd]
    try? task.run()
    task.waitUntilExit()
    return String(data: pipe.fileHandleForWriting.availableData, encoding: .utf8) ?? ""
}

let result = shell("ls -la")
print(result)
```

---

## Exit Codes
```swift
import Foundation

guard CommandLine.arguments.count > 1 else {
    print("Usage: script.swift ")
    exit(1)     // non-zero = error
}

exit(0)         // success
```