linux shell脚本学习笔记(2)

1. for命令

for var in list
do
	commands
done

for test in monday tuesday wednesday thursday friday saturday sunday
do
	echo the test is $test
done

wang@wang:~$ ./test.sh 
the test is monday
the test is tuesday
the test is wednesday
the test is thursday
the test is friday
the test is saturday
the test is sunday

2. 用通配符读取目录

for file in /home/wang/*
do

	if [ -d "$file" ]
	then
		echo "$file is a directory"
	elif [ -f "$file" ]
	then
		echo "$file is a file"
	fi

done

wang@wang:~$ ./test.sh 
/home/wang/90 is a file
/home/wang/a.txt is a file
/home/wang/b.txt is a file
/home/wang/codes is a directory
/home/wang/empty.c is a file

3. C风格for命令

for后面需要使用双括号

for (( a = 1; a < 10; a++ ))
do 
	echo "The number is $a"
done

4. while 命令

while test command
do
	other commands
done

val=10

while [ $val -gt 0 ]
do
	echo $val
	val=$[$val - 1]
done

val=10

使用多个测试条件，只有最后一个状态码决定循环什么时候结束

while echo $val
	[ $val -ge 0 ]
do
	echo "This is inside the loop"
	val=$[$val - 1]
done

wang@wang:~$ ./test.sh 
10
This is inside the loop
9
This is inside the loop
8
This is inside the loop
7
This is inside the loop
6
This is inside the loop
5
This is inside the loop
4
This is inside the loop
3
This is inside the loop
2
This is inside the loop
1
This is inside the loop
0
This is inside the loop
-1

5. until命令

until test commands
do
	other commands
done


val=10

until [ $val -le 0 ]
do
	echo $val
	val=$[ $val - 2 ]
done

wang@wang:~$ ./test.sh 
10
8
6
4
2

6. break命令

for (( a = 10; a >= 0; a--))
do
	echo "$a"
	if [ $a == 5 ]
	then
		break
	fi
done

wang@wang:~$ ./test.sh 
10
9
8
7
6
5

跳出内部循环

for (( a = 1; a < 4; a++))
do
	echo "Outer loop: $a"
	for (( b = 1; b < 100; b++ ))
	do
		echo "Inside loop: $b"
		if [ $b -eq 5 ]
		then
			break
		fi
	done
done

wang@wang:~$ ./test.sh 
Outer loop: 1
Inside loop: 1
Inside loop: 2
Inside loop: 3
Inside loop: 4
Inside loop: 5
Outer loop: 2
Inside loop: 1
Inside loop: 2
Inside loop: 3
Inside loop: 4
Inside loop: 5
Outer loop: 3
Inside loop: 1
Inside loop: 2
Inside loop: 3
Inside loop: 4
Inside loop: 5

跳出外部循环，与上一个脚本不同处，此次为"break 2"

for (( a = 1; a < 4; a++))
do
	echo "Outer loop: $a"
	for (( b = 1; b < 100; b++ ))
	do
		echo "Inside loop: $b"
		if [ $b -eq 5 ]
		then
			break 2
		fi
	done
done

wang@wang:~$ ./test.sh 
Outer loop: 1
Inside loop: 1
Inside loop: 2
Inside loop: 3
Inside loop: 4
Inside loop: 5

7. continue命令

for (( a = 1; a < 10; a++))
do
	if [ $a -gt 5 ]
	then
		continue
	fi
	echo "loop: $a"
done

wang@wang:~$ ./test.sh 
loop: 1
loop: 2
loop: 3
loop: 4
loop: 5