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 delay_key_write delete desc describe deterministic diagnostics directory disable discard disk distinct distinctrow div do double drop dual dumpfile duplicate dynamic each else elseif enable enclosed encryption end ends engine engines enum error errors escape escaped event events every except exchange execute exists exit expansion expire explain export extended extent_size false fast faults fetch fields file file_block_size filter first fixed float float4 float8 flush follows for force foreign format found from full fulltext general generated geometry geometrycollection get get_format global grant grants group group_replication handler hash having help high_priority host hosts hour hour_microsecond hour_minute hour_second identified if ignore ignore_server_ids import in index indexes infile initial_size inner inout insensitive insert insert_method install instance int int1 int2 int3 int4 int8 integer interval into invisible invoker io io_after_gtids io_before_gtids io_thread ipc is isolation issuer iterate join json key keys key_block_size kill language last leading leave leaves left less level like limit linear lines linestring list load local localtime localtimestamp lock locks logfile logs long longblob longtext loop low_priority master master_auto_position master_bind master_connect_retry master_delay master_heartbeat_period master_host master_log_file master_log_pos master_password master_port master_retry_count master_ssl master_ssl_ca master_ssl_capath master_ssl_cert master_ssl_cipher master_ssl_crl master_ssl_crlpath master_ssl_key master_ssl_verify_server_cert master_tls_version master_user match maxvalue max_connections_per_hour max_queries_per_hour max_rows max_size max_updates_per_hour max_user_connections medium mediumblob mediumint mediumtext memory merge message_text microsecond middleint migrate minute minute_microsecond minute_second min_rows mod mode modifies modify month multilinestring multipoint multipolygon mutex mysql_errno name names national natural nchar ndb ndbcluster never new next no nodegroup none not no_wait no_write_to_binlog null number numeric nvarchar offset on one only open optimize optimizer_costs option optionally options or order out outer outfile owner pack_keys page parser partial partition partitioning partitions password phase plugin plugins plugin_dir point polygon port precedes precision prepare preserve prev primary privileges procedure processlist profile profiles proxy purge quarter query quick range read reads read_only read_write real rebuild recover redo_buffer_size redundant references regexp relay relaylog relay_log_file relay_log_pos relay_thread release reload remove rename reorganize repair repeat repeatable replace replicate_do_db replicate_do_table replicate_ignore_db replicate_ignore_table replicate_rewrite_db replicate_wild_do_table replicate_wild_ignore_table replication require reset resignal restore restrict resume return returned_sqlstate returns reverse revoke right rlike rollback rollup rotate routine row_count row_format rtree savepoint schedule schema schemas schema_name second second_microsecond security select sensitive separator serial serializable server session set share show shutdown signal signed simple slave slow smallint snapshot socket some soname sounds source spatial specific sql sqlexception sqlstate sqlwarning sql_after_gtids sql_after_mts_gaps sql_before_gtids sql_big_result sql_buffer_result sql_calc_found_rows sql_no_cache sql_small_result sql_thread sql_tsi_day sql_tsi_hour sql_tsi_minute sql_tsi_month sql_tsi_quarter sql_tsi_second sql_tsi_week sql_tsi_year ssl stacked start starting starts stats_auto_recalc stats_persistent stats_sample_pages status stop storage stored straight_join string subclass_origin subject subpartition subpartitions super suspend swaps switches table tables tablespace table_checksum table_name temporary temptable terminated text than then time timestamp timestampadd timestampdiff tinyblob tinyint tinytext to trailing transaction trigger triggers true truncate type types uncommitted undefined undo undofile undo_buffer_size unicode uninstall union unique unknown unlock unsigned until update upgrade usage use user user_resources use_frm using utc_date utc_time utc_timestamp validation value values varbinary varchar varcharacter variables varying view virtual visible wait warnings week weight_string when where while with without work wrapper write x509 xa xid xml xor year year_month zerofill zone) 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