Function Arguments, Return Codes, and Output Capture

function show_args {
    echo "Function name (via FUNCNAME): ${FUNCNAME[0]}"
    echo "Number of args: $#"
    echo "All args: $@"
    echo "First: $1"
    echo "Second: $2"
}

show_args "alpha" "beta" "gamma"
# Function name: show_args
# Number of args: 3
# All args: alpha beta gamma
# First: alpha
# Second: beta

# Note: $0 inside a function is the SCRIPT name, not the function name
# Use ${FUNCNAME[0]} for the function name

function create_backup {
    local src="${1:?create_backup: source directory required}"
    local dest="${2:?create_backup: destination directory required}"

    if [[ ! -d "$src" ]]; then
        echo "ERROR: source '$src' is not a directory" >&2
        return 1
    fi

    mkdir -p "$dest" || return 1
    cp -r "$src/." "$dest/" || return 1
    echo "Backup complete: $src → $dest"
    return 0
}

# Call and check result
if create_backup "/etc" "/tmp/etc-backup"; then
    echo "Success"
else
    echo "Backup failed" >&2
fi

function get_file_size {
    local file="$1"
    if [[ ! -f "$file" ]]; then
        echo "File not found: $file" >&2    # error → stderr
        return 1                             # signal failure
    fi
    stat -c%s "$file" 2>/dev/null || wc -c < "$file"    # size → stdout
    return 0                                 # signal success
}

# Use it
size=$(get_file_size "/etc/hosts")
if [[ $? -eq 0 ]]; then
    echo "Size: $size bytes"
else
    echo "Could not get size"
fi

# Cleaner idiom:
if size=$(get_file_size "/etc/hosts"); then
    echo "Size: $size bytes"
fi

# Method 1: declare -n nameref (Bash 4.3+)
function print_array {
    local -n arr=$1    # -n makes arr a nameref to the named variable
    for item in "${arr[@]}"; do
        echo "  - $item"
    done
}

fruits=("apple" "banana" "cherry")
print_array fruits    # pass the NAME, not the content

# Method 2: use "$@" when the arguments ARE the array elements
function sum_args {
    local total=0
    for n in "$@"; do (( total += n )); done
    echo "$total"
}

numbers=(1 2 3 4 5)
total=$(sum_args "${numbers[@]}")
echo "Sum: $total"