Convert Dockerfile RUN's

r2a.go

package main

// Dockerfiles build faster when Docker caches the result of your RUN commands. But, the
// resulting image can only be small if the the RUN commands are combined into only one
// RUN command. This script converts Dockerfiles with multiple RUN commands in a row in
// a single RUN command separated by "&& \".

// Use: Run the command while in the current directory to convert the Dockerfile there,
// or give it an optional folder path.

// Install:
// Install Go
// Build with "go build r2a.go"

import (
	"io/ioutil"
	"os"
	"strings"
)

func main() {
	dir := "./"

	if len(os.Args) > 1 {
		arg := os.Args[1]

		if !strings.HasSuffix(arg, "/") {
			dir = os.Args[1] + "/"
		} else {
			dir = os.Args[1]
		}

		if !strings.HasPrefix(arg, "/") {
			dir = "./" + dir
		}
	}

	df, err := ioutil.ReadFile(dir + "Dockerfile")

	if err != nil {
		panic("No Dockerfile in this directory")
	}

	lineSlice := strings.Split(string(df), "\n")

	newDF := ""

	runSeq := false
	for _, line := range lineSlice {
		if strings.HasPrefix(line, "RUN") {
			if runSeq {
				newDF = newDF[:len(newDF)-1]
				newDF += " && \\\n   " + line[3:]
			}
			runSeq = true

			newDF += line + "\n"
			continue
		} else {
			runSeq = false

			newDF += line + "\n"
			continue
		}
	}

	ioutil.WriteFile(dir+"Dockerfile", []byte(newDF), 0644)
}