在函数之间传递数组与关联映射

为什么将数组传递给函数很棘手

my_func "${my_array[@]}"

使用名称引用按名称传递数组

#!/usr/bin/env bash

print_array() {
    declare -n arr="$1"   # nameref: arr -> caller's variable
    echo "Array has ${#arr[@]} elements:"
    for elem in "${arr[@]}"; do
        echo "  - $elem"
    done
}

fruits=(apple banana cherry)
print_array fruits

在函数内部修改调用者的数组

#!/usr/bin/env bash

to_uppercase() {
    declare -n _arr="$1"
    for i in "${!_arr[@]}"; do
        _arr[$i]="${_arr[$i]^^}"   # ^^ = uppercase in Bash 4+
    done
}

words=(hello world bash)
echo "Before: ${words[@]}"
to_uppercase words
echo "After:  ${words[@]}"

通过名称引用返回新数组

#!/usr/bin/env bash

get_even_numbers() {
    local -a source=("$@")
    # Last argument is the output array name — pop it off
    local out_name="${source[-1]}"
    unset 'source[-1]'

    declare -n _out="$out_name"
    _out=()   # clear
    for n in "${source[@]}"; do
        (( n % 2 == 0 )) && _out+=("$n")
    done
}

declare -a evens
get_even_numbers 1 2 3 4 5 6 7 8 evens
echo "Evens: ${evens[@]}"

名称引用冲突陷阱

#!/usr/bin/env bash

# DANGER: caller uses variable named 'arr'
arr=(one two three)

bad_func() {
    declare -n arr="$1"   # collision! arr refers to itself
    echo "${arr[@]}"
}

good_func() {
    declare -n _arr="$1"  # underscore prefix avoids collision
    echo "${_arr[@]}"
}

# bad_func arr   # would hang / error
good_func arr

按名称传递关联数组（映射）

#!/usr/bin/env bash

print_map() {
    declare -n _map="$1"
    echo "Map contents:"
    for key in "${!_map[@]}"; do
        printf '  %-15s => %s\n' "$key" "${_map[$key]}"
    done
}

declare -A config
config[host]="localhost"
config[port]="5432"
config[db]="myapp"

print_map config

使用名称引用合并两个映射

#!/usr/bin/env bash

merge_map() {
    # merge_map dest src
    declare -n _dest="$1"
    declare -n _src="$2"
    for key in "${!_src[@]}"; do
        _dest["$key"]="${_src[$key]}"
    done
}

declare -A defaults=([timeout]=30 [retries]=3 [verbose]=false)
declare -A overrides=([retries]=5 [log_level]=debug)

merge_map defaults overrides

for k in "${!defaults[@]}"; do
    echo "$k = ${defaults[$k]}"
done

间接展开：兼容较旧版本的 Bash

#!/usr/bin/env bash

sum_array() {
    local arr_name="$1"
    # Indirect: build a temporary copy by expanding arr_name[@]
    local -a items
    eval "items=( \"\${${arr_name}[@]}\" )"
    local total=0
    for n in "${items[@]}"; do
        (( total += n ))
    done
    echo "$total"
}

numbers=(10 20 30 40)
result=$(sum_array numbers)
echo "Sum: $result"

构建模块化脚本库

实际示例：返回映射的选项解析器

#!/usr/bin/env bash

parse_opts() {
    declare -n _opts="$1"
    shift
    while [[ $# -gt 0 ]]; do
        case "$1" in
            --host)   _opts[host]="$2";   shift 2 ;;
            --port)   _opts[port]="$2";   shift 2 ;;
            --user)   _opts[user]="$2";   shift 2 ;;
            *)        echo "Unknown option: $1" >&2; shift ;;
        esac
    done
}

declare -A opts=([host]=localhost [port]=5432 [user]=admin)
parse_opts opts --host db.example.com --port 3306

echo "Connecting to ${opts[host]}:${opts[port]} as ${opts[user]}"

在一个函数中组合输入和输出名称引用

#!/usr/bin/env bash

filter_map_by_key_prefix() {
    # Usage: filter_map_by_key_prefix src_map dest_map prefix
    declare -n _src="$1"
    declare -n _dst="$2"
    local prefix="$3"

    _dst=()
    for key in "${!_src[@]}"; do
        if [[ $key == ${prefix}* ]]; then
            _dst["$key"]="${_src[$key]}"
        fi
    done
}

declare -A settings=(
    [db_host]=localhost [db_port]=5432
    [cache_ttl]=300     [cache_driver]=redis
    [app_debug]=true
)
declare -A db_settings

filter_map_by_key_prefix settings db_settings db_

for k in "${!db_settings[@]}"; do
    echo "$k = ${db_settings[$k]}"
done

知识检查：名称引用与数组传递

回顾：在 Bash 中传递复杂数据结构