Go Command Line Parsing

Internal

• Recipes

Overview

Simple access to command line argument is provided by os.Args. os.Args is a string slice that holds the command-line arguments, starting with the program name, which is present on position 0

for i, arg := range os.Args {
    fmt.Printf("argument %d: %s\n", i, arg)
}

Go provides support for command line "flag" parsing in the flag package.

Flags (example: "-path=/something" or "-max=100") are declared with:

sPtr := flag.String("s", ".", "the path vale")
iPtr := flag.Int("i", 1, "the i value")

Note that the flag declaration methods return pointers that can be used to read the value of the flags after parsing:

flag.Parse()

Then their value is read from the previously obtained pointers:

fmt.Println("flag s value: ", *sPtr)
fmt.Println("flag i value: ", *iPtr)

The rest of the command line arguments can be retrieved with flag.Args() that returns a string slice.

In-Line Documentation

If a flag the program does not know about is specified, it produces an output like this:

NOMBP2:bakm ovidiu$ ./output/bakm -version
flag provided but not defined: -version
Usage of ./output/bakm:
  -keep int
    	the number of files to keep in the directory (default 10)

Example

playground/go/command-line-args/command-line-arg-parser.go