【shell】shell条件测试

电玩女神 2023-07-03 07:05 14阅读 0赞

# shell条件测试 #

## 1.测试格式 ##

test 条件表达式，或者\[ 条件表达式 \] ，或者 \[\[ 条件表达式 \]\]，其实我们可以man test查看一下用法

TEST(1)                          User Commands                         TEST(1)
    
    NAME
           test - check file types and compare values
    
    SYNOPSIS
           test EXPRESSION
           test
    
           [ EXPRESSION ]
           [ ]
           [ OPTION

## 2.表达格式 ##

可以按照man test里面的格式要求

( EXPRESSION )
                  EXPRESSION is true
    ! EXPRESSION
                  EXPRESSION is false
    EXPRESSION1 -a EXPRESSION2
                  both EXPRESSION1 and EXPRESSION2 are true
    EXPRESSION1 -o EXPRESSION2
                  either EXPRESSION1 or EXPRESSION2 is true

这里的a可以记忆为and，o可以记为or，比较直接

## 3.文件操作 ##

文件操作，同样还是截取man test里面的参数选择

-b FILE
               FILE exists and is block special
    -c FILE
                  FILE exists and is character special
    -d FILE
                  FILE exists and is a directory
    -e FILE
                  FILE exists
    -f FILE
                  FILE exists and is a regular file
    -g FILE
                  FILE exists and is set-group-ID
    -G FILE
                  FILE exists and is owned by the effective group ID
    -h FILE
                  FILE exists and is a symbolic link (same as -L)
    -k FILE
                  FILE exists and has its sticky bit set
    -L FILE
                  FILE exists and is a symbolic link (same as -h)
    -O FILE
                  FILE exists and is owned by the effective user ID
    -p FILE
                  FILE exists and is a named pipe
    -r FILE
                  FILE exists and read permission is granted
    -s FILE
                  FILE exists and has a size greater than zero
    -S FILE
                  FILE exists and is a socket
    -t FD  file descriptor FD is opened on a terminal
    -u FILE
                  FILE exists and its set-user-ID bit is set
    -w FILE
                  FILE exists and write permission is granted
    -x FILE
                  FILE exists and execute (or search) permission is granted

实例

### 3.1 创建备份文件 ###

创建备份文件，首先判断文件是否存在，文件不存在则创建，开始备份

[klaus@localhost chapt3]$ ls
    test_mysqlback.sh
    [klaus@localhost chapt3]$ cat test_mysqlback.sh
    #!/bin/bash
    back_dir=/home/klaus/Desktop/shell/chapt3/mysqlback
    # if ! test -d $back_dir;then
    if [ ! -d $back_dir ];then
        mkdir -p $back_dir
    fi
    
    echo "start backup..."
    [klaus@localhost chapt3]$ ./test_mysqlback.sh
    start backup...
    [klaus@localhost chapt3]$ ls
    mysqlback  test_mysqlback.sh

这里用到-d，即判断back\_dir是不是一个目录文件

### 3.2 创建用户 ###

创建用户可以用到id user来查看用户是否存在，主要逻辑是首先判断用户是否存在，不存在则创建

[klaus@localhost chapt3]$ sudo userdel -r alice
    [klaus@localhost chapt3]$ id alice
    id: alice: No such user
    [klaus@localhost chapt3]$ cat usradd.sh
    #!/bin/bash
    read -p "please input a username:" user
    
    if id $user &>/dev/null;then
        echo "user $user already exists!"
        exit
    else
        sudo useradd $user
        if [ $? -eq 0 ];then
            echo "User $user created successfully!"
    
        fi
    fi
    [klaus@localhost chapt3]$ ./usradd.sh
    please input a username:alice
    User alice created successfully!
    [klaus@localhost chapt3]$ id alice
    uid=502(alice) gid=502(alice) groups=502(alice)
    [klaus@localhost chapt3]$ ./usradd.sh
    please input a username:alice
    user alice already exists

## 4.数值比较 ##

同样还是截取man test里面的用法

INTEGER1 -eq INTEGER2
                  INTEGER1 is equal to INTEGER2
    INTEGER1 -ge INTEGER2
                  INTEGER1 is greater than or equal to INTEGER2
    INTEGER1 -gt INTEGER2
                  INTEGER1 is greater than INTEGER2
    INTEGER1 -le INTEGER2
                  INTEGER1 is less than or equal to INTEGER2
    INTEGER1 -lt INTEGER2
                  INTEGER1 is less than INTEGER2
    INTEGER1 -ne INTEGER2
                  INTEGER1 is not equal to INTEGER2

记忆方式还是比较简单的equal,greater,less，还是通过几个实例

### 4.1 磁盘分区情况 ###

统计磁盘分区情况，计划每隔一天检查一次，若大于50%则邮件报警

[klaus@localhost chapt3]$ mail
    No mail for klaus
    [klaus@localhost chapt3]$ vim disk_warn.sh
    [klaus@localhost chapt3]$ clear
    [klaus@localhost chapt3]$ mail
    No mail for klaus
    [klaus@localhost chapt3]$ cat disk_warn.sh
    #!/bin/bash
    
    mail_user=klaus
    disk_use=`df -Th|grep '/$'|awk '{print $6}'|awk -F "%" '{print $1}'`
    
    if [ $disk_use -ge 50 ];then
        echo "Disk partition usage is greater than 50%!"
        echo "`date +%F-%H` disk:${disk_use}%" | mail -s "disk warning..." $mail_user
    fi
    [klaus@localhost chapt3]$ ./disk_warn.sh
    Disk partition usage is greater than 50%!
    [klaus@localhost chapt3]$ mail
    Heirloom Mail version 12.4 7/29/08.  Type ? for help.
    "/var/spool/mail/klaus": 1 message 1 new
    >N  1 CenOS6                Sun Feb  2 23:18  18/639   "disk warning..."
    & 1
    Message  1:
    From klaus@localhost.localdomain  Sun Feb  2 23:18:02 2020
    Return-Path: <klaus@localhost.localdomain>
    X-Original-To: klaus
    Delivered-To: klaus@localhost.localdomain
    Date: Sun, 02 Feb 2020 23:18:01 -0800
    To: klaus@localhost.localdomain
    Subject: disk warning...
    User-Agent: Heirloom mailx 12.4 7/29/08
    Content-Type: text/plain; charset=us-ascii
    From: klaus@localhost.localdomain (CenOS6)
    Status: R
    
    2020-02-02-23 disk:52%

然后用crondtab -e加入计划任务

### 4.2 内存报警 ###

当内存使用量达到50%的时候，将报警信息写入对应的文件中去。

[klaus@localhost chapt3]$ mail
    No mail for klaus
    [klaus@localhost chapt3]$ ls
    disk_warn.sh     mysqlback          usradd.sh
    mem_use_warn.sh  test_mysqlback.sh  yum_httpap.sh
    [klaus@localhost chapt3]$ cat mem_use_warn.sh
    #!/bin/bash
    mem_used=`free -m|grep '^Mem'|awk '{print $3}'`
    men_total=`free -m|grep '^Mem'|awk '{print $2}'`
    mem_percent=$[ mem_used*100/men_total ]
    
    mail_user=klaus
    warn_file=/home/klaus/Desktop/shell/chapt3/warn_memory.txt
    
    rm -rf $warn_file
    if [ $mem_percent -ge 50 ];then
        echo "`date +%F_%H` menmory: ${mem_percent}% " > $warn_file
    fi
    
    if [ -f $warn_file ];then
        mail -s "Warning, memory usage is greater than 50%!" $mail_user < $warn_file
        #rm -rf $warn_file
    fi
    [klaus@localhost chapt3]$ ./mem_use_warn.sh
    [klaus@localhost chapt3]$ ls
    disk_warn.sh     mysqlback          usradd.sh        yum_httpap.sh
    mem_use_warn.sh  test_mysqlback.sh  warn_memory.txt
    [klaus@localhost chapt3]$ cat warn_memory.txt
    2020-02-03_00 menmory: 88%
    [klaus@localhost chapt3]$ mail
    Heirloom Mail version 12.4 7/29/08.  Type ? for help.
    "/var/spool/mail/klaus": 1 message 1 new
    >N  1 CenOS6                Mon Feb  3 00:27  18/670   "Warning, memory usage is greater than 50%!"

## 5.字符串比较 ##

同样还是截取man test里面的内容

-n STRING
                  the length of STRING is nonzero
    STRING equivalent to -n STRING
    -z STRING
                  the length of STRING is zero
    STRING1 = STRING2
                  the strings are equal
    STRING1 != STRING2
                  the strings are not equal

\-z表示字符串长度是0，-n表示字符串长度不为0，看一个简单的例子

[klaus@localhost chapt3]$ aaa=""
    [klaus@localhost chapt3]$ echo ${#aaa}
    0
    [klaus@localhost chapt3]$ [ -z "$aaa" ];echo $?
    0
    [klaus@localhost chapt3]$ [ -n "$aaa" ];echo $?
    1

这里有个小细节，为了避免未定义时，比较会报错，统一的加双引号，同时变量为0或者未定义时，长度都是0

### 5.1 实例，批量创建用户 ###

[klaus@localhost chapt3]$ awk -F':' '{ print $1}' /etc/passwd
    root
    ...
    klaus
    win
    [klaus@localhost chapt3]$ cat batch_usradd.sh                  
    #!/bin/bash
    read -p "please input a number: " num
    if [[ "$num" =~ ^[1-9][0-9]+$ ]];then
        echo "Wrong input parameters, please enter a numbers!"
        exit
    fi
    
    read -p "please input prefix: " prefix
    if [ -z "$prefix" ];then
        echo "error prefix!"
        exit
    fi
    
    for i in `seq $num`
    do
        user=$prefix$i
        sudo useradd $user
        echo "123456"|passwd --stdin $user &> /dev/null
        if [ $? -eq 0 ];then
            echo "user $user is created!"
        fi
    done
    [klaus@localhost chapt3]$ ./batch_usradd.sh                  
    please input a number: 2
    please input prefix: tmpuser
    [klaus@localhost chapt3]$ awk -F':' '{ print $1}' /etc/passwd
    root
    ...
    klaus
    win
    user
    tmpuser1
    tmpuser2

上面设计一个正则的表达^\[1-9\]\[0-9\]+$，表达式中的^表示以什么开头，$表示以什么结尾，+代表可以有多个，整个表达可表示成以非0开头的数字

## 6.模式匹配 ##

> case的语法结构为 case 变量 in  
> 模式1）  
> 命令序列  
> ;;  
> 模式2）  
> 命令序列  
> ;;  
> \*）  
> 无匹配后命令序列 esac

### 6.1 实例，删除用户，多匹配 ###

具体思路，首先判断用户是否存在，若存在则询问是否删除，再次确定，执行删除操作

[klaus@localhost chapt3]$ sudo useradd alice
    [klaus@localhost chapt3]$ cat delete_user.sh
    #!/bin/bash
    read -p "Please enter the username to delete:" user
    
    id $user &> /dev/null
    if [ $? -ne 0 ];then
        echo "Error, the user $user does not exist!"
        exit 1
    fi
    
    read -p "Are you sure to delete user $user ? [y/n]" action
    case "$action" in
        y|Y|yes|YES)
            sudo userdel -r $user
            echo "user $user is deleted"
            ;;
        *)
            echo "Run error!"
    esac
    [klaus@localhost chapt3]$ ./delete_user.sh
    Please enter the username to delete:alice
    Are you sure to delete user alice ? [y/n]Y
    user alice is deleted
    [klaus@localhost chapt3]$ id alice
    id: alice: No such user
    [klaus@localhost chapt3]$ ./delete_user.sh
    Please enter the username to delete:alice
    Error, the user alice does not exist!

### 6.2 内存工具信息查看工具 ###

[klaus@localhost chapt3]$ cat infor_tool.sh
    #!/bin/bash
    
    menu(){
        cat<<-EOF
    ##########################################
    #   Linux Information Viewing Toolbox    #
    #                                        #
    #       h.  help                         #
    #       f.  disk partition               #
    #       d.  filesystem mount             #
    #       m.  memory                       #
    #       u.  system load                  #
    #       q.  quit                         #
    ##########################################
    EOF
    }
    
    menu
    while :
    do
        read -p "please input [ h for help ]: " action
        case "$action" in
            h)
                clear;menu;;#(建议下面都加一个clear操作)
            f)
                sudo fdisk -l;;
            d)
                df -Th;;
            m)
                free -m;;
            u)
                uptime;;
            q)
                break;;
           "")
                ;;
            *)
                echo "Run error!"
        esac
    done

运行效果

[klaus@localhost chapt3]$ ./infor_tool.sh  
    ##########################################
    #   Linux Information Viewing Toolbox    #
    #                                        #
    #       h.  help                         #
    #       f.  disk partition               #
    #       d.  filesystem mount             #
    #       m.  memory                       #
    #       u.  system load                  #
    #       q.  quit                         #
    ##########################################
    please input [ h for help ]: f
    
    Disk /dev/sda: 21.5 GB, 21474836480 bytes
    255 heads, 63 sectors/track, 2610 cylinders
    Units = cylinders of 16065 * 512 = 8225280 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk identifier: 0x0003de16
    
       Device Boot      Start         End      Blocks   Id  System
    /dev/sda1   *           1          39      307200   83  Linux
    Partition 1 does not end on cylinder boundary.
    /dev/sda2              39        2358    18631680   83  Linux
    /dev/sda3            2358        2611     2031616   82  Linux swap / Solaris
    please input [ h for help ]: m
                 total       used       free     shared    buffers     cached
    Mem:           979        886         92          3         86        493
    -/+ buffers/cache:        306        673
    Swap:         1983          2       1981
    please input [ h for help ]: q
    [klaus@localhost chapt3]