ruby 35 lines · 7 steps

Building safe shell commands in Ruby

An ArchiveBuilder assembles a tar command from parts, escapes it, and runs it while checking the exit status.

Explained by highlit

Intermediate shell-out subprocess command-injection error-handling service-object

1require "shellwords"
2require "open3"
3 
4module Backup
class ArchiveBuilder
  def initialize(source_dir, destination:, exclude: [])
    @source_dir = source_dir
    @destination = destination
    @exclude = exclude
  end
11 
  def call
    stdout, stderr, status = Open3.capture3(build_command)
    unless status.success?
      raise "tar failed (#{status.exitstatus}): #{stderr.strip}"
    end
    stdout
  end
19 
  private
21 
  def build_command
    parts = ["tar", "--create", "--gzip"]
    parts.concat(exclude_flags)
    parts << "--file" << @destination
    parts << "--directory" << @source_dir
    parts << "."
    Shellwords.join(parts)
  end
30 
  def exclude_flags
    @exclude.flat_map { |pattern| ["--exclude", pattern] }
  end
end
35end

01 / 01

STEP 01

Walkthrough

Space play ←→ step click any line

Three takeaways

1Assembling commands as an array and joining with Shellwords avoids injection from unescaped paths or patterns.
2Open3.capture3 gives you stdout, stderr, and exit status separately so you can react to failures precisely.
3Always check status.success? rather than trusting a subprocess to have done its job silently.

Related explainers

rust

use serde::Deserialize;
 
#[derive(Debug, Deserialize)]
#[serde(untagged)]

Parsing flexible JSON shapes with serde

deserialization enums json

Intermediate 6 steps

ruby

class UserAgentParser
  BROWSERS = [
    [/Edg\/([\d.]+)/, "Edge"],
    [/OPR\/([\d.]+)/, "Opera"],

Parsing user-agent strings in Ruby

regex pattern-matching lookup-tables

Intermediate 8 steps

ruby

class LogAggregator
  BUCKET_FORMAT = "%Y-%m-%dT%H:%M"
 
  def initialize(entries)

Bucketing log entries by the minute in Ruby

aggregation hashing enumerable

Intermediate 5 steps

ruby

class WeeklySignupsReport
  DEFAULT_WEEKS = 12
 
  def initialize(weeks: DEFAULT_WEEKS, source: User.all)

Building a weekly signups report in Rails

service object aggregation group by

Intermediate 7 steps

rust

use chrono::{Duration, NaiveDate};
 
#[derive(Debug)]
pub struct DateRange {

Parsing and iterating date ranges in Rust

error-handling iterators parsing

Intermediate 7 steps

ruby

class ApplicationController < ActionController::Base
  EXPERIMENTS = {
    checkout_button_color: %w[control blue green],
    onboarding_flow: %w[control streamlined]