bash脚本（二）

for循环

for VAR in LIST; do

statements

...

done

LIST列表：

1、直接给出

2、数值列表

{start..end},如{1..10}

seq LAST

seq FIRST LAST

seq FIRST STEP LAST，如seq 1 2 10,会读取到13579

3、特殊变量$#，[email protected]，$*

4、通过命令引用获取的参数列表，如（$(grep ‘bash$‘ /etc/passwd | cut -d: -f3)）

5、通配符读取目录 /tmp/test/*

通过命令引用获取的参数列表

[[email protected] ~]# cat /root/test
aa
bb
cc
dd
ee
[[email protected] ~]# cat test.sh 
#!/bin/bash
declare -i x=1
for i in `cat /root/test`; do
	echo "value$x$count:=$i"
	let x++
done
[[email protected] ~]# bash test.sh 
value1:=aa
value2:=bb
value3:=cc
value4:=dd
value5:=ee

通配符读取目录

[[email protected] ~]# cat test.sh 
#!/bin/bash
declare -i x=1
for i in /tmp/*; do
	echo "value$x$count:=$i"
	let x++
done
[[email protected] ~]# bash test.sh 
value1:=/tmp/test1
value2:=/tmp/test2
value3:=/tmp/test3
value4:=/tmp/test

for的C风格

for (( variable assignment; condition; iteration process)); do

#statements

done

#/bin/bash
for (( a = 1,b=10; a <= 10; a++,b-- )); do
	echo "$a-$b"
done

选择语句

单分支if语句

if [[ condition ]]; then

#statements TRUE

fi

if可以嵌套

if [[ condition ]]; then

if [[ condition ]]; then

#statements

fi

fi

双分支if语句

if [[ condition ]]; then

#statements TRUE

else

#statements FLASE

fi

多分支if语句，哪个condition为TRUE满足则执行下面的statements

if [[ condition ]]; then

elif [[ condition ]]; then

#statements

elif [[ condition ]]; then

#statements

else

#statements

fi

case语句

case word in

pattern )

;;

pattern )

;;

pattern )

;;

* )

;;

esac

pattern可使用通配符：

*：任意长度的任意字符

?: 任意单个字符

[]：指定范围内的任意单个字符

a|b: a或者b

[[email protected] ~]# cat test.sh
#!/bin/bash
read -p "Enter a choice" choice
case ${choice:-b} in
	a) echo "a";;
	b) echo "b";;
	c) echo "b";;
esac
[[email protected] ~]# bash test.sh 
Enter a choice
b

while，until语句

while [[ condition TRUE ]]; do

#statements

修正表达式否则会死循环

done

until [[ condition FALSE ]]; do

#statements

修正表达式否则会死循环

done

1x1=1	1x2=2	1x3=3	1x4=4	1x5=5	1x6=6	1x7=7	1x8=8	1x9=9	
2x2=4	2x3=6	2x4=8	2x5=10	2x6=12	2x7=14	2x8=16	2x9=18	
3x3=9	3x4=12	3x5=15	3x6=18	3x7=21	3x8=24	3x9=27	
4x4=16	4x5=20	4x6=24	4x7=28	4x8=32	4x9=36	
5x5=25	5x6=30	5x7=35	5x8=40	5x9=45	
6x6=36	6x7=42	6x8=48	6x9=54	
7x7=49	7x8=56	7x9=63	
8x8=64	8x9=72	
9x9=81	
#!/bin/bash
declare -i i=1
declare -i j=1
while [[ $i -lt 10 ]]; do
    let j=$i
    until [[ $j -gt 9 ]]; do
	echo -e -n "${i}x${j}=$[$i*$j]\t"
	let j++
    done
    let i++
    echo
done

9x9=81	
8x8=64	8x9=72	
7x7=49	7x8=56	7x9=63	
6x6=36	6x7=42	6x8=48	6x9=54	
5x5=25	5x6=30	5x7=35	5x8=40	5x9=45	
4x4=16	4x5=20	4x6=24	4x7=28	4x8=32	4x9=36	
3x3=9	3x4=12	3x5=15	3x6=18	3x7=21	3x8=24	3x9=27	
2x2=4	2x3=6	2x4=8	2x5=10	2x6=12	2x7=14	2x8=16	2x9=18	
1x1=1	1x2=2	1x3=3	1x4=4	1x5=5	1x6=6	1x7=7	1x8=8	1x9=9
#!/bin/bash
declare -i i=9
while [[ $i -gt 0 ]]; do
    j=$i
    until [[ $j -gt 9 ]]; do
	echo -e -n "${i}x${j}=$[$i*$j]\t"
	let j++
    done
    echo 
    let i--
done

while的特殊用法

[[email protected] ~]# cat /tmp/test
aa aa aa aa
bb bb bb bb
cc cc cc cc
#!/bin/bash
count=1
cat /tmp/test | while read line; do
    echo "Line $count:$line"
    let count++
done
#!/bin/bash
count=1
while read line; do
    echo "Line $count:$line"
    let count++
done < /tmp/test

2个脚本的效果一样
Line 1:aa aa aa aa
Line 2:bb bb bb bb
Line 3:cc cc cc cc

break可以退出进行中的循环的一个简单方法

[[email protected] ~]# cat test.sh 
#!/bin/bash
for i in {1..10}; do
    if [ $i -eq 5 ];then
	break
    fi
    echo "$i"  
done
[[email protected] ~]# bash test.sh 
1
2
3
4

continue命令是提早结束执行循环内部的命令但不完全终止整个循环的一个途径

[[email protected] ~]# cat test.sh 
#!/bin/bash
for i in {1..15}; do
	if [[ $i -gt 1 ]] && [[ $i -lt 14 ]]; then
		continue
	fi
	echo "$i"
done
[[email protected] ~]# bash test.sh 
1
14
15