我今天在写一个 ssh 免密脚本，然后发现执行效率极低，换了种写法，发现一秒以内运行完成，添加提示信息发现了一个没想明白的情况，我提炼了具体情况，还请各位老哥解个惑

精简的代码贴上：

#!/bin/bash
declare -a EXTRAARG=("$@")

MySQLKeywords=(accessible account action add after against aggregate algorithm all alter always analyze and any as asc ascii asensitive at autoextend_size auto_increment avg avg_row_length backup before begin between bigint binary binlog bit blob block bool boolean both btree by byte cache call cascade cascaded case catalog_name chain change changed channel char character charset check checksum cipher class_origin client close coalesce code collate collation column columns column_format column_name comment commit committed compact completion component compressed compression concurrent condition connection consistent constraint constraint_catalog constraint_name constraint_schema contains context continue convert cpu create cross current current_date current_time current_timestamp current_user cursor cursor_name data database databases datafile date datetime day day_hour day_microsecond day_minute day_second deallocate dec decimal declare default default_auth definer delayed 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for GROUP_NAME in "${EXTRAARG[@]}";do
    GROUP_NAME=$(echo "${GROUP_NAME}"|tr "[:upper:]" "[:lower:]")
    # echo "tr 转换的数组元素: ${GROUP_NAME}"

    # 0.7s 一个纯字母，一个字母中有一个冒号
    if [[ "${GROUP_NAME}" =~ ":" ]]; then
        GROUP_NAME1=$(echo "${GROUP_NAME}"|cut -d':' -f 1)
        GROUP_NAME2=$(echo "${GROUP_NAME}"|cut -d':' -f 2)
        if [ -n "$(echo "${GROUP_NAME}"|cut -d':' -f 3)" ];then
            _error "非法字符: $(echo "${GROUP_NAME}"|cut -d':' -f 3)" && exit 1
        else
            for j in "${MySQLKeywords[@]}";do
                if [ "${GROUP_NAME1}" = "$j" ] || [ "${GROUP_NAME2}" = "$j" ];then
                    _error "参数不能为 MySQL 的关键字或保留字！退出中" && exit 1
                fi
            done
        fi
    elif [[ ! "${GROUP_NAME}" =~ ":" ]]; then
        for j in "${MySQLKeywords[@]}";do
                if [ "${GROUP_NAME}" = "$j" ];then
                    _error "参数不能为 MySQL 的关键字或保留字！退出中" && exit 1
                fi
        done
    fi


    # 7s 一个纯字母，一个字母中有一个冒号
    for j in "${MySQLKeywords[@]}";do
        if [[ "${GROUP_NAME}" =~ ":" ]]; then
            GROUP_NAME1=$(echo "${GROUP_NAME}"|cut -d':' -f 1)
            GROUP_NAME2=$(echo "${GROUP_NAME}"|cut -d':' -f 2)
            if [ -n "$(echo "${GROUP_NAME}"|cut -d':' -f 3)" ];then
                _error "非法字符: $(echo "${GROUP_NAME}"|cut -d':' -f 3)" && exit 1
            elif [ "${GROUP_NAME1}" = "$j" ] || [ "${GROUP_NAME2}" = "$j" ];then
                _error "参数不能为 MySQL 的关键字或保留字！退出中" && exit 1
            fi
        elif [[ ! "${GROUP_NAME}" =~ ":" ]]; then
            if [ "${GROUP_NAME}" = "$j" ];then
                _error "参数不能为 MySQL 的关键字或保留字！退出中" && exit 1
            fi
        fi
    done
    
    
    
done

脚本功能

1. 以上脚本声明了两个数组变量，一个是从用户输入获取的参数，另一个相当长的是 mysql 的默认关键字和保留字
2. 脚本读取并遍历用户输入的信息，每一个信息都进 mysql 关键字数组遍历对比，发现是 mysql 保留字就报错退出。
3. 脚本中有两种循环写法，运行时间差距极大，对比测试运行时需要注释掉一组

脚本流程

用户给脚本提供两种格式的变量，一个是纯大小写字母，一个是字母中有一个英文冒号分隔符，但只能有一个冒号存在，即之后利用冒号进行变量字符的拆分的时候，最多只会拆成两个字符串。

我输入了两个变量：asdf 和 asd:f

后文加粗代表操作相同 简单来说，同样有外部遍历循环套着，区别在于：

• 龟速的是内部用遍历套着一组 if 判断
• 高速的是一组 if 判断各自套着一组内部遍历

7 秒龟速循环流程

采用循环内使用 if 进行分支判断

1. 获取两个变量的数组后对两个变量进行遍历，为外部循环
2. 每获取一个外部循环进来的变量就立即进入对 sql 关键字数组遍历的内部循环
3. 对外部循环进来的单个变量检查是否包含冒号
4. 如果有冒号，就根据冒号进行分割成两个字符串
5. 检测按冒号分割，会不会有第三个非空字符串，如果存在，则报错退出
6. 将拆分出来的两个字符串分别对比关键字数组遍历时的那轮关键字，如果任意一个字符串与该轮循环的 sql 关键字相同则报错退出，到此带冒号的遍历流程完毕
7. 如果没冒号，则将变量直接对比关键字数组遍历时的那轮关键字，如果俩字符串相同则报错退出

0.7 秒高速循环流程

采用 if 进行分支判断后送入各自的循环

1. 获取两个变量的数组后对两个变量进行遍历，为外部循环
2. 每获取一个外部循环进来的变量就检查是否包含冒号
3. 如果有冒号，就根据冒号进行分割成两个字符串
4. 检测按冒号分割，会不会有第三个非空字符串，如果存在，则报错退出
5. 否则进入对 sql 关键字数组遍历的内部循环
6. 将拆分出来的两个字符串分别对比关键字数组遍历时的那轮关键字，如果拆分出来的两个字符串中任意一个与该轮循环的 sql 关键字相同则报错退出，到此带冒号的遍历完毕
7. 如果没冒号，则将变量直接对关键字数组遍历，如果数组中存在相同字符串则报错退出