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1.2 Command-Line Arguments

os.Args Variable

The os package provides functions and other values for dealing with the operating system in a platform-independent fashion.

Command-line arguments are available to a program in a variable named Args that is part of the os package; thus its name anywhere outside the os package is os.Args.

Slices

The variable os.Args is a slice of strings. Slices are a fundamental notion in Go, and we’ll talk a lot more about them soon. For now, think of a slice as

• a dynamically sized sequence s of ‘array’ elements where individual elements can be accessed as s[i] and a contiguous subsequence as s[m:n].
• The number of elements is given by len(s).
• As in most other programming languages, all indexing in Go uses half-open intervals that include the first index but exclude the last, because it simplifies logic.
• For example, the slice s[m:n], where ‘0 ≤ m ≤ n ≤ len(s)’, contains ‘n-m’ elements.

Elements of Slice

1. The first element of os.Args, os.Args[0], is the name of the command itself;
2. the other elements are the arguments that were presented to the program when it started execution.
3. A slice expression of the form s[m:n] yields a slice that refers to elements ‘m’ through ‘n-1’, so the elements we need for our next example are those in the slice os.Args[1:len(os.Args)]. If ‘m’ or ‘n’ is omitted, it defaults to 0 or len(s) respectively, so we can abbreviate the desired slice as os.Args[1:].

• Echo1
• Echo2
• Echo3
• Exercises