shell 笔记 之控制结构
if 语句：#!/bin/bash# if 语句格式：# if 和then放在不同行，并使else和结束处必须的fi与它们水平对齐if [ "${1}" = '' ]then echo no argument input .else echo first argument is : $1fivar=2echo "${var}"if [ "${var}" = "1" ]then echo one .elif [ "${var}" = "2" ]then echo two .elif [ "${var}" = "3" ]then echo three .else echo at least four .fi
for循环：
#!/bin/bash# in 关键字后面是字列表，for x in one two three fourdo echo number $xdonefor var in "$@"do echo you pass in $vardone# 使用文件通配符for myfile in /etc/r*do if [ -d "$myfile" ] then echo "$myfile is dir" else echo "$myfile" fidone# 还可以在字列表中使用多个通配符，甚至是变量# 可以使用相对路径或绝对路径；对于相对路径，bash是相对于当前工作目录执行通配符扩展。for x in ./*var/lo* /home/${USER}/*do echo $xdone while和until 循环：
#!/bin/bashecho use while loop control .myvar=0while [ $myvar -ne 10 ]do echo $myvar myvar=$(( $myvar + 1 ))doneechoechoecho use until loop control .myvar=10until [ $myvar -eq 0 ]do echo $myvar myvar=$(( $myvar - 1 ))done
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