“go build” and “go install”

Let's tidy up the $GOPATH directory and only keep Go source code files left over:

# tree
.
├── bin
├── pkg
└── src
    ├── greet
    │   └── greet.go
    └── hello
        └── hello.go

5 directories, 2 files

The greet.go is greet package which just provides one function:

# cat src/greet/greet.go
package greet

import "fmt"

func Greet() {
        fmt.Println("Hello 中国!")
}

While hello.go is a main package which takes advantage of greet and can be built into an executable binary:

# cat src/hello/hello.go
package main

import "greet"

func main() {
        greet.Greet()
}

(1) Enter the src/hello directory, and execute go build command:

# pwd
/root/gowork/src/hello
# go build
# ls
hello  hello.go
# ./hello
Hello 中国!

We can see a fresh hello command is created in the current directory.

Check the $GOPATH directory:

# tree
.
├── bin
├── pkg
└── src
    ├── greet
    │   └── greet.go
    └── hello
        ├── hello
        └── hello.go

5 directories, 3 files

Compared before executing go build, there is only a final executable command more.

(2) Clear the $GOPATH directory again:

# tree
.
├── bin
├── pkg
└── src
    ├── greet
    │   └── greet.go
    └── hello
        └── hello.go

5 directories, 2 files

Running go install in hello directory:

# pwd
/root/gowork/src/hello
# go install
#

Check the $GOPATH directory now:

# tree
.
├── bin
│   └── hello
├── pkg
│   └── linux_amd64
│       └── greet.a
└── src
    ├── greet
    │   └── greet.go
    └── hello
        └── hello.go

6 directories, 4 files

Not only the hello command is generated and put into bin directory, but also the greet.a is in the pkg/linux_amd64. While the src folder keeps clean with only source code files in it and unchanged.

(3) There is -i flag in go build command which will install the packages that are dependencies of the target, but won't install the target. Let's check it:

# tree
.
├── bin
├── pkg
└── src
    ├── greet
    │   └── greet.go
    └── hello
        └── hello.go

5 directories, 2 files

Run go build -i under hello directory:

# pwd
#/root/gowork/src/hello
# go build -i

Check $GOPATH now:

# tree
.
├── bin
├── pkg
│   └── linux_amd64
│       └── greet.a
└── src
    ├── greet
    │   └── greet.go
    └── hello
        ├── hello
        └── hello.go

Except a hello command in src/hello directory, a greet.a library is also generated in pkg/linux_amd64 too.

(4) By default, the go build uses the directory's name as the compiled binary's name, to modify it, you can use -o flag:

# pwd
/root/gowork/src/hello
# go build -o he
# ls
he  hello.go

Now, the command is he, not hello.