在Shell脚本中，使用`if`语句进行复杂的条件判断

在Shell脚本中，使用if语句进行复杂的条件判断时，可以结合多种条件测试命令和逻辑运算符来实现。以下是一些复杂条件判断的例子：

示例1：多条件与（and）操作

#!/bin/bash

# 判断两个条件是否同时为真
value1=5
value2="Hello"

if [ "$value1" -eq 5 ] && [ "$value2" = "Hello" ]; then
    echo "Both conditions are true"
else
    echo "At least one condition is false"
fi

示例2：多条件或（or）操作

#!/bin/bash

# 判断两个条件是否有任意一个为真
file1_exists=$(test -e file1.txt; echo $?)
file2_exists=$(test -e file2.txt; echo $?)

if [ "$file1_exists" -eq 0 ] || [ "$file2_exists" -eq 0 ]; then
    echo "At least one file exists"
else
    echo "Neither file exists"
fi

# 或者更简洁的写法：
if test -e file1.txt || test -e file2.txt; then
    echo "At least one file exists"
else
    echo "Neither file exists"
fi

示例3：嵌套if语句

#!/bin/bash

number=10

if [ "$number" -gt 0 ]; then
    if [ "$number" -lt 20 ]; then
        echo "The number is between 0 and 20 (inclusive)"
    else
        echo "The number is greater than 20"
    fi
else
    echo "The number is less than or equal to 0"
fi

# 使用双括号[[ ]]语法简化嵌套条件
if [[ $number -gt 0 && $number -lt 20 ]]; then
    echo "The number is between 0 and 20 (inclusive) using double brackets"
fi

示例4：模式匹配与文件测试结合

#!/bin/bash

filename="example.log"

if [[ -f "$filename" && "$filename" == *.log ]]; then
    echo "The file '$filename' exists and has the .log extension"
else
    echo "The file either doesn't exist or doesn't have the .log extension"
fi

以上是几种常见的复杂条件判断场景，通过组合不同的条件测试和逻辑运算符，可以在Shell脚本中构建更加复杂和精细的控制流程。