文章目录

• 1. 单括号[] 和 test
• • 1.1 文件相关判断
  • 1.2 字符串相关判断
  • 1.3 整型判断
  • 1.4 多个判断连接
• 2. 双括号[[ ]]

1. 单括号[] 和 test

左括号[和test本质是一样的，是shell的内部命令，所以>和<等会被解释为重定向符号，而不是比较符号：

bash-3.2$ type [ [[ test
[ is a shell builtin
[[ is a shell keyword
test is a shell builtin

右括号]表示判断结束，可以通过man [查看支持的判断语句：

$ man [

1.1 文件相关判断

• -d file: True if file exists and is a directory.
• -f file: True if file exists and is a regular file.
• -h file: True if file exists and is a symbolic link.
• -S file: True if file exists and is a socket.
• file1 -nt file2: True if file1 exists and is newer than file2.

1.2 字符串相关判断

• string: True if string is not the null string.
• s1 = s2: True if the strings s1 and s2 are identical.
• s1 < s2: True if string s1 comes before s2 based on the binary value of their characters.

1.3 整型判断

• n1 -eq n2: True if the integers n1 and n2 are algebraically equal.
• n1 -ne n2: True if the integers n1 and n2 are not algebraically equal.
• n1 -gt n2: True if the integer n1 is algebraically greater than the integer n2.
• n1 -ge n2: True if the integer n1 is algebraically greater than or equal to the integer n2.
• n1 -lt n2: True if the integer n1 is algebraically less than the integer n2.
• n1 -le n2: True if the integer n1 is algebraically less than or equal to the integer n2.

1.4 多个判断连接

• ! expression: True if expression is false.
• expression1 -a expression2: True if both expression1 and expression2 are true.
• expression1 -o expression2: True if either expression1 or expression2 are true.

2. 双括号[[ ]]

双括号是shell的关键字，会返回一个状态码，所以也可以作为判断条件使用。（更加通用）

• [[支持字符串的模式匹配，=~支持正则匹配
• [[返回状态码，所以可以与shell中的 &&和||一起使用：

$ [[ 1 < 2 ]] && echo "1 < 2" || echo "1 >= 2"
1 < 2