shell条件测试

一.命令执行结果判定

&& 在命令执行后如果没有任何报错时会执行符号后面的动作

|| 在命令执行后如果命令有报错会执行符号后的动作

示例：

[root@qingdeng shell3]# sh sl.sh
/mnt/file is not exist
no

二.条件判断方法

在 shell 程序中，用户可以使用测试语句来测试指定的条件表达式的条件的真或假

[root@qingdeng shell3]# a=1
[root@qingdeng shell3]# b=1
[root@qingdeng shell3]# test $a = $b && echo yes || echo no
yes

[root@qingdeng shell3]# a=1
[root@qingdeng shell3]# b=2
[root@qingdeng shell3]# [ "$a" = "$b" ] && echo yes || echo no~
no~

[root@qingdeng shell3]# a=2
[root@qingdeng shell3]# [[ $a =~ 2|10 ]] && echo yes || echo no
yes

[root@qingdeng shell3]# a=3
[root@qingdeng shell3]# (( $a>0,$a<10 )) && echo yes
yes

三.判断表达式

3.1.文件判断表达式

a ）判断文件时否存在

[root@qingdeng shell3]# [ -a "file" ] && echo yes || echo no
no
[root@qingdeng shell3]# touch file
[root@qingdeng shell3]# [ -a "file" ] && echo yes || echo no
yes

b ）判断文件类型

[root@qingdeng shell3]# [ -d /mnt ] && echo /mnt is directory
/mnt is directory

c ）判定文件是否存在并不为空

[root@qingdeng shell3]# [ -s file ] || echo file is not exist or file is empty file
file is not exist or file is empty file
[root@qingdeng shell3]# ll file
-rw-r--r-- 1 root root 0 12月  8 20:53 file

d ）判定文件权限

[root@qingdeng shell3]# [ -x file ] || echo file is not execute
file is not execute

e ）判定文件新旧

[root@qingdeng shell3]# touch file1
[root@qingdeng shell3]# [ file -ot file1 ] && echo yes
yes

3.2.字符串测试表达式

1. 检测变量是否未空

[root@qingdeng shell3]# b=hello
[root@qingdeng shell3]# [ -z "$b" ] && echo yes
[root@qingdeng shell3]# [ -z "$b" ] && echo yes || echo no
no
[root@qingdeng shell3]# [ -n "$b" ] && echo yes || echo no
yes

2. 比较字符

[root@qingdeng shell3]# a=quite
[root@qingdeng shell3]# [ "$a" = "b" ] && echo yes || echo no
no

四.练习脚本

要求

[root@haha ~]# sh checkfile.sh
please input filename: 当未输入任何字符时回车
Error： no checkfilename，Please input filename for check ！！ 报错
please input filename: /mnt/leefile 当输入/mnt/leeifle时
文件不存在时
/mnt/file is not exist
当文件存在时输入文件类型
/mnt/file is commom file 注意文件是什么类型就输出文件类型的相关输出

[root@qingdeng shell]# sh checkfile.sh
please input filename: 

Error： no checkfilename，Please input filename for check ！！
[root@qingdeng shell]# sh checkfile.sh
please input filename: 
file
file is not exist
[root@qingdeng shell]# sh checkfile.sh
please input filename: 
/mnt/file
/mnt/file is commom file

五.整数测试表达式

[root@qingdeng shell3]# a=1
[root@qingdeng shell3]# b=2
[root@qingdeng shell3]# [ $a -eq $b ] && echo yes || echo no
no
[root@qingdeng shell3]# [ $a -ne $b ] && echo yes || echo no
yes
[root@qingdeng shell3]# [ $a -ge $b ] && echo yes || echo no
no
[root@qingdeng shell3]# [ $a -gt $b ] && echo yes || echo no
no
[root@qingdeng shell3]# [ $a -le $b ] && echo yes || echo no
yes
[root@qingdeng shell3]# [ $a -lt $b ] && echo yes || echo no
yes

六.逻辑操作符

[root@qingdeng shell3]# a=5
[root@qingdeng shell3]# [ "$a" -gt "0" -a "$a" -lt "10" ] && echo yes
yes
[root@qingdeng shell3]# [ "$a" -gt "0" ] && echo yes
yes
[root@qingdeng shell3]# [ "$a" -lt "0"   -o "$a" -gt "10" ] && echo yes
[root@qingdeng shell3]# [ "$a" -lt "0"   -o "$a" -gt "10" ] || echo yes
yes

七.判定综合训练

1. 请用判定的方式书写一个 1 分 10 秒的倒计时，确保倒计时器符合日常显示规则

2. 请书写一个猜数游戏，要求如下

[root@qingdeng shell]# sh guest_number.sh
please input a number between 0 ~ 9:
Error：Please input a number between 0 - 9
please input a number between 0 ~ 9:4
  4 is too small
please input a number between 0 ~ 9:6
  6 is too big
please input a number between 0 ~ 9:5
 HAHAHA!!! 
 YES You are right ！！
Please again？（y/n）y
please input a number between 0 ~ 9:4
  4 is too big
please input a number between 0 ~ 9:3
  3 is too big
please input a number between 0 ~ 9:2
  2 is too big
please input a number between 0 ~ 9:1
  1 is too big
please input a number between 0 ~ 9:0
 HAHAHA!!! 
 YES You are right ！！
Please again？（y/n）y
please input a number between 0 ~ 9:44
Error： is not between 0 ~ 9，Please input a number between 0 - 9
please input a number between 0 ~ 9:

原文地址：https://blog.csdn.net/2301_78668665/article/details/144331251

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