`CommandLine`

Swift can be used to develop command-line programs, and it can handle command-line arguments. With this language we can access arguments from the CommandLine type.

The first string in the CommandLine arguments array is the file name of the program being run. We can remove this with range syntax.

Example

To use this program, we need to run it from the command line. It is possible to save it in a text file, and then from the command line, run the "swift" command on it.

Step 1 We access the arguments array from the CommandLine type. We can use the expression directly or store it in a local variable.

Step 2 Like any array in Swift, we can access the element with the count property. This includes the initial element (the file name).

Step 3 We can loop over the entire array and print each value, which is a string value.

Step 4 With range syntax, we can remove the initial file name argument from the array. This can simplify some loops.

Step 5 Here is a for-loop that uses switch on each argument (past the first). We can handle arguments in a real program this way.

// Step 1: get command line arguments.
let args = CommandLine.arguments

// Step 2: print count of arguments.
print("COUNT:", args.count)

// Step 3: print command line arguments.
for arg in args {
    print("ARG:", arg)
}

// Step 4: skip over program file name.
for arg in args[1...] {
    print("SKIPPED ARG:", arg)    
}

// Step 5: switch on arguments.
for arg in args[1...] {
    switch arg {
    case "argument1":
        print("FIRST ARG")
    case "argument2":
        print("SECOND ARG")
    default:
        print("?")
    }
}swift program.swift argument1 argument2
COUNT: 3
ARG: program.swift
ARG: argument1
ARG: argument2
SKIPPED ARG: argument1
SKIPPED ARG: argument2
FIRST ARG
SECOND ARG

Swift provides the CommandLine.arguments array which can be accessed in command-line programs. This feature simplifies how we access arguments to the current program being run.