Go cli

Introduction

This is just a page on go command options

go help <command>
// e.g.
go help test

We can go to https://golang.org/cmd/go/ for online

Building and Running

Environment

For me I have set up my PATH to include go and my GOROOT to be the parent directory of the src folder.

export PATH=/usr/local/go/bin:$PATH
cd blah1/blah2/src/..
export GOPATH=`pwd`

Run

Compiles and run a program without leaving artefacts.

go run src/cmds/hello/hello.go

Build

Compiles but does not run a program. Given the tree

This command will build the library but not produce anything.

go build hello

This command will build the binary and produce a binary

go build cmds/hello

Adding the -i forces the intermediate files to be created on disk in the pkg directory

go build -i cmds/hello

Install

Go install will do all of what build will do but will also create the bin and the library in the workspace. e.g.

go install cmds/hello

Other Commands

So here are some other flags

-a force rebuild
-n dry run with verbose
-n no dry run with verbose
-p for processors
-v verbose

Race Flag

This is a flag to detect issues with concurrency adding this to the run can help find issues. Just run the code with -race. Without the shadowing to local scope this code would fail.

package main

import "fmt"
import "sync"

func main() {
        var wg sync.WaitGroup
        for i := 0; i < 10; i++ {
                wg.Add(1)
// ===>>>                i := i
                go func() {
                        fmt.Println(i)
                        wg.Done()
                }()
        }
        wg.Wait()
}

Running with -race will help

==================
WARNING: DATA RACE
Read at 0x00c0000160b0 by goroutine 7:
  main.main.func1()
      /home/iwiseman/dev/courses/go-cli/03/demos/demos/03-race/main.go:12 +0x3c

Previous write at 0x00c0000160b0 by main goroutine:
  main.main()
      /home/iwiseman/dev/courses/go-cli/03/demos/demos/03-race/main.go:8 +0x108

Goroutine 7 (running) created at:
  main.main()
      /home/iwiseman/dev/courses/go-cli/03/demos/demos/03-race/main.go:11 +0xe4
==================

Shared Libraries

This did not impress. We have to build the standard library doing

sudo /usr/local/go/bin/go build -buildmode=shared std

Just do not like the sudo, guess in a container not a problem. Anyway we just need to build the program

go build -linkshared cmds/hello

C/C++ Integration

Static Linking

We can link go archives to C by

• Include "C" package
• Creating an empty main (no idea why)
• Add comment with export name - note no space

package main

import "fmt"
import "C"

func main() {}

//export Hello
func Hello() {
        fmt.Println("Hello")
}

Next issue the build mode command which will produce an include hello.h

go build -buildmode=c-archive hello.go

From there we are good to go - no pun intended

cc test.c ./hello.a -;pthread

Dynamic Linking

No surprises except of course the crappyness to the approach with export comments. I really think they are just trying to keep the precious keyword count down

go build -buildmode=c-shared hello.go