[]with[[]]
[brand@localhost ~]$ echo $name hello
hello
[brand@localhost ~]$ [$name = "hello"]
-bash: [: missing `]' #[ ] 与变量要有间隔
[brand@localhost ~]$ [ $name = "hello" ]
-bash: [: =: unary operator expected# 包含$,分词影响
[brand@localhost ~]$ [[ $name = "hello" ]]
[brand@localhost ~]$ echo $? [brand@localhost ~]$ [[ "$name" = "hello" ]]
[brand@localhost ~]$ echo $? [brand@localhost ~]$ [ "$name" = "hello" ]
[brand@localhost ~]$ echo $? [brand@localhost ~]$
[]是shell内嵌的命令,会执行
[[]]是usr/bin/test
(( ))用于数字计算
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