SHELL—条件判断与练习

最新推荐文章于 2024-07-02 14:33:34 发布

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#学习笔记

本文详细介绍了Shell脚本中进行条件判断的方法，包括数值和字符串比较，以及如何检查文件的各种属性，如是否存在、是否为空、文件类型等。通过实际示例，展示了如何判断一个输入数字是否在特定范围内，以及如何识别不同类型的文件。

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一.条件判断

test "$a" == "$b" 等同于 [ "$a" == "$b" ]

[ "$a" = "$b" ]		##等于
[ "$a" != "$b" ]	##不等于
[ "$a" -eq "$b" ]	##等于
[ "$a" -ne "$b" ]	##不等于
[ "$a" -le "$b" ]	##小于等于
[ "$a" -ge "$b" ]	##大于等于
[ "$a" -gt "$b" ]	##大于
[ "$a" -lt "$b" ]	##小于
[ "$a" -ne "$b" -a "$a" -gt "$b" ]	##-a必须条件都满足
[ "$a" -ne "$b" -o"$a" -gt "$b" ]	##-a条件至少满足一个
[ -z "$a" ]		##是否为空
[ -e "file" ]		##是否存在
[ -f "file" ]		##普通文件
[ -b "file" ]		##块设备
[ -S "file" ]		##套接字
[ -c "file" ]		##字符设备
[ -L "file" ]		##软链接

二.练习

判断输入的数字是否在10以内

       1.输入是否为空
       2.是否在10以内
       3.1<$a<10 --> yes
       4.$a<1 $a>10 --> no

#!/bin/bash

[ -z "$1" ] && {
    echo "please input a number!"
    exit 1
}

[ "$1" -gt "0" -a "$1" -lt "10" ] && {
    echo "YES"
}||{
    echo "NO"
}

判断文件类型

[root@localhost mnt]# vim file.sh 
[root@localhost mnt]# cat file.sh 
#!/bin/bash
[ -z "$1" ] && {
    echo "please enter the file name"
    exit 1
}
[ -e "$1" ] || {
    echo "this file does not exist"
    exit 1
}

[ -f "$1" ] && {
    echo "the file is a normal file"
}

[ -b "$1" ] && {
    echo "the file is a block device"
}
[ -S "$1" ] && {
    echo "the file is a normal socket"
}
[ -c "$1" ] && {
    echo "the file is a character device"
}
[ -L "$1" ] && {
    echo "the file is a soft link"
}
[root@localhost mnt]# sh file.sh test.sh 
the file is a normal file