SHELL脚本中常用的控制结构 & Shell循环

从网上收集而来，自己学习的同时也可以作为一个备份以供随时参考：

if … then语句

if [ test_command ]
then
commands
fi

if … then … else语句

if [ test_command ]
then
  commands
else
  commands
fi

if … then … elif … (else)语句

if [ test_command ]
then
  commands
elif [ test_command ]
then
  commands
...
...
else (optional)
  commands
fi

for … in语句

for 变量 in 变量列表
do
  commands
done

while语句

while 条件为真
do
  commands
done

until语句

until 条件为真
do
  commands
done

case语句

case $variable in
match_1)
commands_to_execute_for_1
;;
match_2)
commands_to_execute_for_2
;;
match_3)
commands_to_execute_for_3
;;
...
...
*) (可选 - any other value)
commands_to_execute_for_no_match
;;
esac

来源： <http://blog.csdn.net/jubincn/article/details/7288632>

Shell循环

#数字段形式
for i in {1..10}
do
echo $i
done

#详细列出（字符且项数不多）
for File in 1 2 3 4 5
do
echo $File
done

#对存在的文件进行循环
for shname in `ls *.sh`
do
name=`echo “$shname” | awk -F. ‘{print $1}’`
echo $name
done

#查找循环（ls数据量太大的时候也可以用这种方法）
for shname in `find . -type f -name “*.sh”`
do
name=`echo “$shname” | awk -F/ ‘{print $2}’`
echo $name
done

#(())语法循环–有点像C语法，但记得双括号
for((i=1;i<100;i++))
do
if((i%3==0))
then
echo $i
continue
fi
done

#seq形式起始从1开始
for i in `seq 100`
do
if((i%3==0))
then
echo $i
continue
fi
done

#while循环注意为方括号[]，且注意空格
min=1
max=100
while [ $min -le $max ]
do
echo $min
min=`expr $min + 1`
done

#双括号形式，内部结构有点像C的语法，注意赋值：i=$(($i+1))
i=1
while(($i<100))
do
if(($i%4==0))
then
echo $i
fi
i=$(($i+1))
done

整体示例如下：

#!/bin/bash

for((i=0; i<10; i++));do
	echo $(expr $i * 4)
done

for i in $(seq 10);do
	echo $i
done

i=1
while(($i<10));do
	echo $i
	i=`expr $i + 1`
done

for i in {1..10};do
	echo $i
done

for i in {01..10};do
	echo $i
done

for i in {a..z};do
	echo $i
done

for i in $(ls);do
	echo $i
done

for i in `ls`;do
	echo $i
done

for i in f1 f2 f3;do
	echo $i
done

cat /tmp/drops.txt | while read url title
do
    title=$(echo $title | tr ' </' '_')
    curl -s $url | sed -n '/<div id="content">/,/entry-tags/p' >/tmp/tmp.html
    cat /tmp/top.html /tmp/tmp.html /tmp/bottom.html >/tmp/$title.html
done

while read url title
do
    title=$(echo $title | tr ' </' '_')
    curl -s $url | sed -n '/<div id="content">/,/entry-tags/p' >/tmp/tmp.html
    cat /tmp/top.html /tmp/tmp.html /tmp/bottom.html >/tmp/$title.html
done < /tmp/drops.txt

####
dir=(papers tips tools news web pentesting database binary)
dir_num=${#dir[@]}
for((i=0;i<$dir_num;i++))
do
	for j in $(seq 1 15)
	do
	if [ "$j" == 1 ]
	then
		echo http://drops.wooyun.org/category/${dir[i]}
	else
		echo http://drops.wooyun.org/category/${dir[i]}/page/$j
	fi
	done
done
####

arr=("a" "b" "c")
echo "arr is (${arr[@]})"

arr=(a b c)
for i in ${arr[@]}
do
	echo $i
done


echo "参数,$*表示脚本输入的所有参数："
for i in $* ; do
	echo $i
done

EGREP=/bin/egrep
COUNTRY=('cn' 'hk' 'tw')
for c in ${COUNTRY[@]}
do
    wget "http://www.ipdeny.com/ipblocks/data/countries/$c.zone"
    country_file=$c.zone
    IPS=$($EGREP -v "^#|^$" $country_file)
    for ip in $IPS
    do
        echo "blocking $ip"
        iptables -A INPUT -s $ip -j DROP
    done
done

# SHELL数组详解
# http://ixyzero.com/blog/archives/178.html
$ A=(a b c def)

$ echo ${A[@]}		#取全部元素
a b c def

$ echo ${A[0]}		#取第一个元素
a

$ echo ${#A[@]}		#取得数组元素的个数
4

$ echo ${#A[3]}		#取得第4个元素的长度
3

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