Announcing shellquote

In my effort to port certain tools to go I’ve authored another package: github.com/frioux/shellquote.

Imagine you are generating a shell script based in part on input from a user. In this theoretical example the user might be passing a list of files and you are generating a command that they can tweak and re-run later. You could assume that their filenames are “normal” but eventually someone will have a space in the filename.

The first obvious solution is to just wrap each filename in single quotes ('). Then of course users cannot have quotes in their filenames. This module generically solves this problem.

🔗 github.com/frioux/shellquote

Here’s an example of usage:

package main

import (
	"fmt"
	"os"

	"github.com/frioux/shellquote"
)

func main() {
	quoted, err := shellquote.Quote(os.Args[:1])
	if err != nil {
		fmt.Fprintf(os.Stderr, "Couldn't quote args: %s\n", err)
		os.Exit(1)
	}
	fmt.Println("#!/bin/sh")
	fmt.Println("")
	fmt.Println("cool-command", quoted)
}

The other use-case I know of is for generating ssh(1) commands. To correctly run a remote command via ssh actually requires shell quoting twice; once for the local machine and once for the remote machine. This can get confusing pretty quickly. The included shellquote example shows how you can use it to generate ssh commands:

package main

import (
	"fmt"
	"os"

	"github.com/frioux/shellquote"
)

func main() {
	fmt.Println("#!/bin/sh")
	fmt.Println("")
	quoted, err := shellquote.Quote(os.Args[1:])
	if err != nil {
		fmt.Fprintf(os.Stderr, "Couldn't quote input: %s\n", err)
		os.Exit(1)
	}
	// error won't happen if the first input didn't error
	doublequoted, _ := shellquote.Quote([]string{quoted})
	fmt.Println("ssh superserver", doublequoted)
}

This is a module I don’t find myself needing much, but the cases do come up and it’s great to have a real solution.

The logic of this module originally came from the similarly named Perl module: String::ShellQuote

Writing this was pleasant. Thankfully the Perl version came with a pretty solid test suite that I was able to port over. It’s simpler than the original version both because Go doesn’t have exceptions and because I suspect that a “best effort quote” function is probably broken.

(The following includes affiliate links.)

If you want to learn more about Go I strongly recommend The Go Programming Language by Donovan and Kernighan. I’ve mentioned it many, many times on this blog before. It’s one of the best programming books I’ve ever read and I read the entire thing.

Another helpful book, if you like writing shell scripts, is From Bash to Z Shell. This book goes over powerful features in the most popular shells nowadays: bash and zsh. While I write programs in POSIX shell (aka Bourne Shell) I do use zsh interactively and take advantage of many features to save typing. This book is one of the few technical books I’ve taken with me over multiple moves.

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