The main package

Learn that the main package is the program entry point.

The main package

In Go, the package named main is special: when the module containing it is compiled, an executable binary is produced. All other packages are libraries and cannot run directly.

The main package must contain func main(). When the program starts, this function is called. The main package can have multiple .go files; they all belong to the same package.

To produce the executable binary, you use the go build command.

Library packages

Packages other than main are libraries. For example, a file with package utils is part of the utils package. You use it from another package with import.

Library packages cannot run directly; they are only called by other packages. This lets you split your code into modules.

Exported (capital-letter) names in a package are reachable from other packages. Lowercase names stay package-private.

Exercise The main package and function

Write the two requirements of an executable program: package main and func main(). In main, call a helper function named selam(); selam prints "program başladı".

Show example solution

package main

import "fmt"

func selam() {
    fmt.Println("program başladı")
}

func main() {
    selam()
}

Test yourself

Which function is required inside the main package?
- func start()
- func main()
- func run()
- func init()
Show answer

func main() — The main package must contain func main().

Package declaration

For an executable program:
____ main

Show answer

For an executable program:
package main

Match the package kinds

main

Executable
utils

Library
fmt

Standard library
github.com/x/y

Third party

Next lesson: Multiple files

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