Functions & Arguments

Intermediate ⭐ 80 XP ⏱ 16 min #bash#functions

Structure scripts with reusable functions, parameters, and return values.

📖Theory

Functions group related logic so scripts stay readable and DRY. Inside a function, arguments are $1, $2, $@ — just like a script. A function communicates back in two ways:

Exit status via return N (0–255) — for success/failure
Output via echo captured with result=$(myfunc) — for actual data

Use local to scope variables inside a function so they don’t leak into the global namespace and cause spooky bugs.

🌍Real-World Example

#!/usr/bin/env bash

log() {                          # a helper used everywhere
  local level="$1"; shift
  echo "[$level] $*"
}

add() {
  local sum=$(( $1 + $2 ))
  echo "$sum"                     # output, captured by caller
}

is_even() {
  (( $1 % 2 == 0 )) && return 0 || return 1
}

log INFO "starting"
total=$(add 3 4)                  # total = 7
if is_even "$total"; then log INFO "even"; else log INFO "odd"; fi

✍️Hands-On Exercise

Write a greet function that takes a name and prints a greeting.
Write a function that returns success/failure based on whether a file exists.
Use local to prove a variable doesn’t leak outside the function.
Capture a function’s echoed result into a variable and use it.

🧾Cheat Sheet▾

Item	Syntax
Define	`name() { … }`
Arguments	`$1 $2 $@ $*`
Local variable	`local x=…`
Return status	`return N` (0–255)
Shift args	`shift`
Capture output	`r=$(func args)`

💬Common Interview Questions▾

How does a Bash function return a value?

Two channels: return sets an exit status (0–255) for success/failure, while data is returned by echoing it and capturing with $(func).

Why use local in functions?

It scopes a variable to the function so it doesn’t overwrite or leak into global variables — preventing subtle bugs in larger scripts.

📚Official Documentation

↗ Bash — Shell Functions

📝 My notes on this topic

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