Function Parameters

#!/bin/bash
greet() {
    echo "Hello, $1! You are $2 years old."
}
greet "Ada" 36

#!/bin/bash
sum_two() {
    if [ "$#" -ne 2 ]; then
        echo "Error: expected exactly 2 arguments, got $#"
        return 1
    fi
    echo "Sum: $(( $1 + $2 ))"
}
sum_two 3 4
sum_two 3 || echo "Handled the argument-count error gracefully"

#!/bin/bash
log_message() {
    echo "[LOG] $*"
}
notify_all() {
    log_message "$@"
}
notify_all "System" "started successfully"

#!/bin/bash
set_volume() {
    local level="${1:-50}"
    echo "Volume set to $level"
}
set_volume 80
set_volume

1. Assuming a function can access the caller's local variables by name automatically; unless explicitly passed as an argument (or the variable is global), a function only sees what is given to it via $1, $2, etc.
2. Confusing a function's $1 with the script's own $1; inside a function, the positional parameters are temporarily replaced with the function's own call arguments, shadowing the script-level ones for the duration of the call.
3. Forgetting to quote "$@" when forwarding a function's arguments to another command, causing arguments with spaces to be split apart.

• Inside a function, $1, $2, ... refer to that function's own arguments, not the script's original command-line arguments.
• $# inside a function gives the number of arguments passed to that specific function call.
• "$@" inside a function expands to all of that function's arguments, each preserved as a separate word when quoted.
• Functions do not require declaring parameter names ahead of time -- you simply reference $1, $2, etc. wherever needed in the body.