循环

嵌套循环处理文件数据

#! /bin/bash
IFS=$'\n'
for entry in $(cat /etc/passwd)
do
    echo "Values in $entry"
    IFS=':'
    for value in $entry
    do
        echo $value
    done    
done


Values in root:x:0:0:root:/root:/bin/bash
root
x
0
0
root
/root
/bin/bash

break跳出内部循环

[root@iZbp11f8g5h7oozejqy6k6Z shell]# sh test7.sh 
Outer loop:1
    Inner loop:1
    Inner loop:2
    Inner loop:3
    Inner loop:4
Outer loop:2
    Inner loop:1
    Inner loop:2
    Inner loop:3
    Inner loop:4
Outer loop:3
    Inner loop:1
    Inner loop:2
    Inner loop:3
    Inner loop:4
[root@iZbp11f8g5h7oozejqy6k6Z shell]# cat test7.sh 
#! /bin/bash
for (( a = 1; a < 4; a++))
do
    echo "Outer loop:$a"
    for (( b = 1; b < 100; b++))
    do
        if [ $b -eq 5 ]
        then
            break
        fi
        echo "    Inner loop:$b"
    done
done

break跳出外部循环

break n

n指定了要跳出的循环层级

[root@iZbp11f8g5h7oozejqy6k6Z shell]# sh test7.sh 
Outer loop:1
    Inner loop:1
    Inner loop:2
    Inner loop:3
    Inner loop:4
[root@iZbp11f8g5h7oozejqy6k6Z shell]# cat test7.sh 
#! /bin/bash
for (( a = 1; a < 4; a++))
do
    echo "Outer loop:$a"
    for (( b = 1; b < 100; b++))
    do
        if [ $b -eq 5 ]
        then
            break 2
        fi
        echo "    Inner loop:$b"
    done
done

创建多个账户

[root@iZbp11f8g5h7oozejqy6k6Z shell]# sh test9.sh 
adding rich
adding chrinstine
adding barbara
adding tim
[root@iZbp11f8g5h7oozejqy6k6Z shell]# cat test9.sh 
#! /bin/bash
while IFS=',' read -r userid name
do 
    echo "adding $userid"
    useradd -c "$name" -m $userid
done < user.txt
[root@iZbp11f8g5h7oozejqy6k6Z shell]# cat user.txt 
rich,Richard Blum
chrinstine,Christine Bresnahan
barbara,Barbara Blum
tim,Timothy Bresnahan

[root@iZbp11f8g5h7oozejqy6k6Z shell]# tail -n 4 /etc/passwd
rich:x:1001:1001:Richard Blum:/home/rich:/bin/bash
chrinstine:x:1002:1002:Christine Bresnahan:/home/chrinstine:/bin/bash
barbara:x:1003:1003:Barbara Blum:/home/barbara:/bin/bash
tim:x:1004:1004:Timothy Bresnahan:/home/tim:/bin/bash