shell脚本6--循环，比较

for循环

for var in list;

　　commands;#使用变量$var

done

example:

　　for i in {a..z}; do actions; done;

后者

for((i=0;i<10;i++))

{

　　commands;

}

while condition

　　commands;

done

until循环

example:

x=0;

until [ $x -eq 9 ];

　　let x++; echo $x;

done

if比较语句

if contions;

then

　　commands;

else if和else语句

if condition;

then

　　commands;

else if conditon;then

　　commands;

else

　　commands;

简洁用法：

[ condition ] && action;

[ condition ] || action;

算数比较：
[ $var -eq 0 ]

[ $var -ne 0 ]

逻辑与和逻辑或

[ $var1 -ne 0 -a $var2 -gt 2 ]

[ $var1 -ne 0 -o $var2 -gt 2 ]

example:

#!/bin/bash

#filename:compare.sh

fpath="/etc/passwd"

if [ -e $fpath ]; then

    echo file exits;

else

    echo does not exists;

fi

巴特西