-x 在 if 条件语句中是什么意思？

Question

-x这里是什么意思：

if [ -x /etc/rc.local ] then

我怎么能找到这个手册页if？

Answer 1

从man bash页面（尤其是条件表达式部分）：

   -a file
          True if file exists.
   -b file
          True if file exists and is a block special file.
   -c file
          True if file exists and is a character special file.
   -d file
          True if file exists and is a directory.
   -e file
          True if file exists.
   -f file
          True if file exists and is a regular file.
   -g file
          True if file exists and is set-group-id.
   -h file
          True if file exists and is a symbolic link.
   -k file
          True if file exists and its ``sticky'' bit is set.
   -p file
          True if file exists and is a named pipe (FIFO).
   -r file
          True if file exists and is readable.
   -s file
          True if file exists and has a size greater than zero.
   -t fd  True if file descriptor fd is open and refers to a terminal.
   -u file
          True if file exists and its set-user-id bit is set.
   -w file
          True if file exists and is writable.
   -x file
          True if file exists and is executable.

   [...]

Answer 2

if本身是一个 shell 关键字，因此您可以使用help if. if本身仅根据下一个命令返回 true ( 0 ) 还是 false ( 非零) 来进行分支。不过，您真正想要的是man [or man test， where[是test. 该语句实际上正在执行test -x /etc/rc.local，它测试该文件是否存在并且是否可执行（或具有搜索权限）。