过程式编程
选择执行
顺序执行: if, case
循环执行: for, while, until
for循环列表
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for i in LIST; do
循环体
done
for i in LIST
do
循环体
done
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while循环
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while CONDITION; do
循环体
done
while CONDITION
do
循环体
done
CONDITION 循环控制条件,每执行一次循环体，需要再次进行判断
true时，执行一次循环
false时，退出循环
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练习：100以内所有正整数之和
练习: 100以内所有偶数和
练习:添加10个用户
练习:通过ping命令探测172.16.250.1-254范围内的所有主机的在线状态.用while循环
练习：打印9x9乘法表
练习：利用RANDOM生成10个随机数，输出这10个数字，并显示其中最大者和最小者
练习：100以内所有正整数之和
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#!/bin/bash
declare -i sum=0
for i in {1..100}; do
let sum=$sum+1
done
echo $i
echo "summary: $sum"
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#!/bin/bash
#
declare -i sum=0
declare -i i=1
while [ $i -le 100 ]; do
sum=$[$sum+$i]
let i++
done
echo $i
echo "summary: $sum"
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练习: 100以内所有偶数和
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#!/bin/bash
#
declare -i sum=0
declare -i i=2
while [ $i -le 100 ]; do
sum=$[$sum+$i]
let i+=2
done
echo $i
echo "summary: $sum"
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练习:添加10个用户user1-user10
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#!/bin/bash
declare -i i=1
declare -i users=0
while [ $i -le 10 ]; do
id user$i &> /dev/null
retval=$?
[ $retval -ne 0 ] && useradd user$i &> /dev/null
[ $? -eq 0 ] && echo "Add user user$i finished" && let users=$users+1
done
echo "Add $users users"
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练习:通过ping命令探测172.16.250.1-254范围内的所有主机的在线状态.用while循环
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#!/bin/bash
#
declare -i IP='172.16.250.'
declare -i i=1
declare -i uphosts=0
declare -i downhosts=0
while [ $i -le 254 ]; do
if ping -c 1 -w 1 $IP$i &> /dev/null; then
echo "$IP$i is up"
let uphosts++
else
echo "$IP$i is down"
let downhosts++
fi
done
echo "uphosts: $uphosts"
echo "downhosts: $downhosts"
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练习：打印9x9乘法表
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#!/bin/bash
#
for i in {1..9}; do
for j in $(seq 1 1 $i); do
echo -ne "${j}X${i}=$[$i*$j]\t"
j=$(($j+1))
done
echo
done
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#!/bin/bash
#
declare -i i=1
while [ $i -le 9 ]; do
declare -i j=1
while [ $j -le $i ]; do
echo -ne "${j}X${i}=$[$i*$j]\t"
j=$(($j+1))
done
echo
i=$(expr $i + 1)
done
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练习：利用RANDOM生成10个随机数，输出这10个数字，并显示其中最大者和最小者
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#!/bin/bash
#
declare -i max=
declare -i min=
declare -i i=1
declare -i random
while [ $i -le 10 ]; do
random=$RANDOM
echo $random
if [ $i -eq 1 ]; then
max=$random
min=$max
fi
if [ $i -gt 1 ]; then
if [ $random -gt $max ]; then
max=$random
fi
if [ $random -lt $min ]; then
min=$random
fi
fi
let i++
done
echo "max: $max"
echo "min: $min"
==========================================
#!/bin/bash
#
declare -i max=
declare -i min=
declare -i i=1
declare -i random
while [ $i -le 10 ]; do
random=$RANDOM
echo $random
if [ $i -eq 1 ]; then
max=$random
min=$max
fi
if [ $random -gt $max ]; then
max=$random
fi
if [ $random -lt $min ]; then
min=$random
fi
let i++
done
echo "max: $max"
echo "min: $min"
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本文转自 lccnx 51CTO博客，原文链接：http://blog.51cto.com/sonlich/1964037，如需转载请自行联系原作者
Linux系统安全及应用
