Linux

Part 1 covered how to define and call functions. Part 2 is about making them robust — how functions report success or failure, how to stop a script when something breaks, and how to catch errors before they cascade. These techniques separate a fragile script from one you can trust in production. Key point: In…

59 – shell functions flow control and if Flow control is what turns a script from a straight line of commands into a program that makes decisions. The if statement is the most important of these — it lets you run different code depending on whether a condition is true or false. Combined with operators…

The test command is the engine behind every if condition you’ve written so far. [ … ] is actually a synonym for test — they do exactly the same thing. Understanding test directly makes your scripts clearer and helps you avoid quoting bugs. Key point: test evaluates a conditional expression and returns an exit status…

The older [ ] test has been around since the earliest days of Unix. [[ ]] is bash’s modern replacement — it fixes the quoting headaches, adds regex and pattern matching, and generally makes conditions safer to write. And (( )) is its arithmetic counterpart — a cleaner way to do integer math than expr…

Loops are how a script repeats work. Instead of writing the same command ten times, you write it once and let the loop run it ten times. Bash gives you two main conditional loops — while and until — plus for for iterating over lists. This chapter covers while and until; for comes next. Key…

When you have one value to check against many possible patterns, a chain of if/elif/else gets ugly fast. The case statement is the cleaner alternative — it matches a value against a list of patterns and runs the first block that matches. Key point: case compares a single value against multiple patterns. Each pattern ends…

The for loop is the most-used loop in shell scripting. Where while and until repeat until a condition changes, for iterates over a known list of items — numbers, words, files, command output. It’s the loop you reach for when you know what you’re looping over. Key point: Bash gives you five ways to write…

Parameter expansion is what turns bash variables from simple placeholders into a real text-processing toolkit. With a single ${…} expression you can extract substrings, provide defaults, replace patterns, strip prefixes and suffixes, and get the length — all without calling external commands like sed, cut, or awk. Key point: Parameter expansion happens inside the shell…

Converting strings to uppercase or lowercase comes up constantly — normalizing user input, formatting output, comparing values case-insensitively. Bash gives you four different ways to do it, each with different trade-offs in portability, speed, and readability. Key point: The fastest and cleanest method is bash’s built-in parameter expansion (${var^^} and ${var,,}). The most portable is…

Bash arithmetic works in decimal by default, but it can handle octal, hexadecimal, and binary too. Converting between bases is a common task — file permissions, memory addresses, bitmasks, and color codes all use non-decimal bases at some point. Key point: Bash’s arithmetic $((…)) can read numbers in any base using prefixes (0 for octal,…