go-command-chain

A go library for easy configure and run command chains. Such like pipelining in unix shells.

Example

cat log_file.txt | grep error | wc -l

package main

import (
	"fmt"
	"github.com/rainu/go-command-chain"
)

func main() {
	stdOut, stdErr, err := cmdchain.Builder().
		Join("cat", "log_file.txt").
		Join("grep", "error").
		Join("wc", "-l").
		Finalize().RunAndGet()

	if err != nil {
		panic(err)
	}
	if stdErr != "" {
		panic(stdErr)
	}
	fmt.Printf("Errors found: %s", stdOut)
}

package main

import (
	"fmt"
	"github.com/rainu/go-command-chain"
)

func main() {
	stdOut, stdErr, err := cmdchain.Builder().
		JoinShellCmd(`cat log_file.txt | grep error | wc -l`).
		Finalize().RunAndGet()

	if err != nil {
		panic(err)
	}
	if stdErr != "" {
		panic(stdErr)
	}
	fmt.Printf("Errors found: %s", stdOut)
}

For more examples how to use the command chain see examples.

Why you should use this library?

If you want to execute a complex command pipeline you could come up with the idea of just execute one command: the shell itself such like to following code:

package main

import (
	"os/exec"
)

func main() {
	exec.Command("sh", "-c", "cat log_file.txt | grep error | wc -l").Run()
}

But this procedure has some negative points:

• you must have installed the shell - in correct version - on the system itself
  • so you are dependent on the shell
• you have no control over the individual commands - only the parent process (shell command itself)
• pipelining can be complex (redirection of stderr etc.) - so you have to know the pipeline syntax
  • maybe this syntax is different for shell versions

(advanced) features

input injections

Multiple different input stream for each command can be configured. This can be useful if you want to forward multiple input sources to one command.

package main

import (
	"github.com/rainu/go-command-chain"
	"strings"
)

func main() {
	inputContent1 := strings.NewReader("content from application itself\n")
	inputContent2 := strings.NewReader("another content from application itself\n")

	err := cmdchain.Builder().
		Join("echo", "test").WithInjections(inputContent1, inputContent2).
		Join("grep", "test").
		Join("wc", "-l").
		Finalize().Run()

	if err != nil {
		panic(err)
	}
}

forking of stdout and stderr

Stdout and stderr of each command can be forked to different io.Writer.

package main

import (
	"bytes"
	"github.com/rainu/go-command-chain"
)

func main() {
	echoErr := &bytes.Buffer{}
	echoOut := &bytes.Buffer{}
	grepErr := &bytes.Buffer{}
	
	err := cmdchain.Builder().
		Join("echo", "test").WithOutputForks(echoOut).WithErrorForks(echoErr).
		Join("grep", "test").WithErrorForks(grepErr).
		Join("wc", "-l").
		Finalize().Run()

	if err != nil {
		panic(err)
	}
}