Shell Scripting : Day #2

Ahoy, crew—welcome to Day 2 of our shell scripting adventure! Yesterday, we set sail with the basics and now it’s time to grab the anchor and plunge a bit deeper. By the end of today, you’ll be whipping up bash scripts, using powerful search tools, and fishing files out of massive directories like a pro captain scanning the horizon!

Been a long time right? That might be a thing to fret upon but as i compensate & try to be more regular this time, here’s the link for Lecture 2: https://missing.csail.mit.edu/2020/shell-tools/

1. What Makes Bash Scripting Special?

Before we start scripting, why do we use Bash and not Python or Ruby? Well, Bash is tailor-made for shell tasks—gluing commands, handling files, and dealing with input/output in a breeze. It’s like having a toolkit designed to repair your ship, not build an entire new one.

2. Variables & Strings with a Twist

Assigning variables in Bash? Easy, but mind the syntax:

bashname="ShellSailor"
echo $name

No spaces around the =! Otherwise, Bash gets confused and tries to run mysterious programs named name.

Strings? Single vs. double quotes matter:

• 'Hello $name' – Literal, prints $name

• "Hello $name" – Magic! Expands variable, prints Hello ShellSailor

Test it out in your shell. You'll see why quotes matter!

3. Captain's Tools: Control Flow (if, else, for, while, functions)

Scripting’s real power? Making decisions and repeating tasks!

If-else Example:

bash#!/bin/bash
if [ "$name" = "ShellSailor" ]; then
  echo "Welcome aboard, sailor!"
else
  echo "Identify yourself!"
fi

For Loop Goodness:

bashfor i in 1 2 3; do
  echo "Row $i"
done

Function Magic:

bashmake_and_cd() {
  mkdir "$1" && cd "$1"
}
make_and_cd seashell

Functions let you bundle commands and pass arguments, just like a real programming language!

4. Passing Arguments: The Secret Language of Scripts

How do scripts get external info? Through special variables:

• $0 : Script name

• $1, $2, ... : Arguments passed

• $@ : All arguments

• $# : Number of arguments

bash#!/bin/bash
echo "Script name: $0"
echo "First argument: $1"
echo "Number of arguments: $#"

Run this as ./script.sh hello world to see the magic.

5. Exit Codes, Short-circuiting, & Command Substitution

Every command leaves a trace as an exit code: 0 = success, anything else = trouble!

Tip: Chain commands for battle-hardened scripts:

• cmd1 && cmd2 – runs cmd2 only if cmd1 succeeded

• cmd1 || cmd2 – runs cmd2 only if cmd1 failed

To capture command output into a variable:

bashcurrent_date=$(date)
echo "Ship’s log date: $current_date"

6. Pattern Matching: Globbing & Curly Braces

Globbing lets you work with groups of files using wildcards:

• *.txt – every text file

• ??.sh – any 2-character .sh file

Curly Braces: Expand repetitive commands:

bashmv file{1,2,3}.txt backup/
# moves file1.txt, file2.txt, file3.txt to backup/

Super handy for batch moves or renames!

7. Script vs. Function: Pick Your Weapon

Shebang lines (#!/usr/bin/env python3) make sure the right interpreter runs your script!

8. Finding Files, Code, & Shell Commands—Like a Pro

🗂️ Finding Files

• find . -name "*.sh" – Find all .sh files recursively!

• Modern pirates use fd for a smoother ride:
  fd mypattern . – much faster & prettier output

🔍 Finding by Content

• grep -rn "myfunction" . – Find every file mentioning "myfunction"

• Try rg (ripgrep) for warp speed:
  rg "main" – recursively, colorized, ignores .git

⏳ Shell History Magic

• history | grep "find" – See commands with "find"

• Ctrl + r – Interactive fuzzy search in your shell history

• Want more? Install fzf for blazingly fast and fuzzy command recall.

9. Bonus Crew Tools: Fast Navigation & More

Ship captains don't waste time typing cd commands! Use:

• fasd / autojump : Jump to frequently used directories with a quick shortcut (e.g. j my_project)

• tree . : Visualize your file structure (see how deep your ship’s hold goes!)

• nnn / ranger : Terminal file managers for serious looting

10. Boarding Exercises: Level Up Your Skills

Try these on your own ship:

1. ls Mastery: Write a command to list all files (including hidden), colorized, by recency, with human-friendly sizes.

2. Home Port Saver: Bash functions port and gotoport that save and return you to directories.

3. Reliability Roulette: Bash script that repeats a command until it fails, logging all output and counting attempts.

4. HTML Treasure: Command to recursively find all .html files and zip them—spaces in filenames won't sink your ship. (Hint: find, xargs, and zip)

5. File Hunter: Script to list all files by modification date—what’s been changing on your vessel?

🏴‍☠️ Parting Waves

Today, you’ve armed yourself with advanced Bash scripting skills, supercharged your search capabilities, and got a taste for shell power tools. Play with every code sample, tweak them, break them, and see what happens. That’s how all great shell masters are made!

Tomorrow, we voyage further—data wrangling ahoy!

Keep shellin’ & sailin’ and see you on deck for Day 3, sailor!

Bleed code!