sudo apt install ruby-full        # system ruby, fine for scripts
ruby -v; irb                      # repl
gem install bundler --user-install

System gems need sudo (sudo gem install x): prefer gem install –user-install or rbenv if you need a newer ruby:

# rbenv route (only if system ruby is too old)
sudo apt install rbenv ruby-build
rbenv install -l | tail           # list versions
rbenv install 3.3.0 && rbenv global 3.3.0

Ruby one-liners:

ruby -e 'puts File.readlines("f").grep(/error/).size'          # count matches
ruby -pe 'sub(/foo/, "bar")' -i file.txt                       # sed-ish in-place
ruby -rjson -e 'j=JSON.parse(STDIN.read); puts j["key"]' < f.json

Script skeleton:

#!/usr/bin/env ruby
abort "usage: #{$0} FILE" if ARGV.empty?
File.readlines(ARGV[0], chomp: true).each { |l| puts l.upcase }

sudo apt install nodejs npm       # distro version (older but fine)
node -v; node script.js           # run
node                              # repl

For a modern Node (nvm is the usual route):

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.40.0/install.sh | bash
nvm install --lts

npm init -y                       # package.json
npm install <pkg>                 # local dep
npx <tool>                        # run without installing

Node skeleton:

#!/usr/bin/env node
const fs = require("fs");
const [,, file] = process.argv;
if (!file) { console.error("usage: script FILE"); process.exit(1); }
console.log(fs.readFileSync(file, "utf8"));

sudo apt install lua5.4
lua5.4 -i script.lua              # run then repl

#!/usr/bin/env lua5.4
for line in io.lines(arg[1]) do print(line:upper()) end

perl -pi -e 's/old/new/g' *.txt          # in-place replace across files
perl -ne 'print if /error/' log.txt      # grep
perl -lane 'print $F[2]' data.txt        # awk-ish column extract
perl -MJSON::PP -0777 -ne 'print decode_json($_)->{key}' f.json

• bash: glue, system tasks, anything <100 lines
• python: default for anything with logic, parsing, APIs
• ruby: if you're fluent; good one-liners and text munging
• node: JS-heavy work, npx tooling, web-shaped data
• lua: conky config; rarely a general scripting pick here
• perl: superior one-liner when sed/awk get awkward

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