嵌套循环(内循环):一条循环语句可以在循环中使用任何类型的命令，包括其他循环命令
示例1：
#!/bin/bash
for (( a = 1; a <= 3; a++ ))
do
echo "Starting loop $a"
for (( b = 1; b <= 3; b++ ))
do
echo "Inside loop $b"
done
done
[[email protected] ~]# ./test14.sh
Starting loop 1
Inside loop 1
Inside loop 2
Inside loop 3
Starting loop 2
Inside loop 1
Inside loop 2
Inside loop 3
Starting loop 3
Inside loop 1
Inside loop 2
Inside loop 3
示例2：
#!/bin/bash
var1=3
while [ $var1 -ge 0 ]
do
echo "Outer loop:$var1"
for (( var2 = 1; $var2 < 3; var2++ ))
do
var3=$[ $var1 * $var2 ]
echo "Inner loop:$var1 * $var2 = $var3"
done
var1=$[ $var1 -1 ]
done
[[email protected] ~]# ./test15.sh
Outer loop:3
Inner loop:3 * 1 = 3
Inner loop:3 * 2 = 6
Outer loop:2
Inner loop:2 * 1 = 2
Inner loop:2 * 2 = 4
Outer loop:1
Inner loop:1 * 1 = 1
Inner loop:1 * 2 = 2
Outer loop:0
Inner loop:0 * 1 = 0
Inner loop:0 * 2 = 0
示例3：
#!/bin/bash
var1=3
until [ $var1 -eq 0 ]
do
echo"Outer loop:$var1"
var2=1
while [ $var2 -lt 5 ]
do
var3=`echo "scale=4; $var1 / $var2" | bc`
echo "Inner loop:$var1 / $var2 = $var3"
var2=$[ $var2 + 1 ]
done
var1=$[ $var1 -1 ]
done
[[email protected] ~]# ./test16.sh
./test16.sh: line 5: echoOuter loop:3: command not found
Inner loop:3 / 1 = 3.0000
Inner loop:3 / 2 = 1.5000
Inner loop:3 / 3 = 1.0000
Inner loop:3 / 4 = .7500
./test16.sh: line 5: echoOuter loop:2: command not found
Inner loop:2 / 1 = 2.0000
Inner loop:2 / 2 = 1.0000
Inner loop:2 / 3 = .6666
Inner loop:2 / 4 = .5000
./test16.sh: line 5: echoOuter loop:1: command not found
Inner loop:1 / 1 = 1.0000
Inner loop:1 / 2 = .5000
Inner loop:1 / 3 = .3333
Inner loop:1 / 4 = .2500