command [-pVv] command [arg …]
Run command with args suppressing the normal shell function lookup. Only builtin commands or commands found
in the PATH are executed. If the -p option is given, the search for command is performed using a default
value for PATH that is guaranteed to find all of the standard utilities. If either the -V or -v option is
supplied, a description of command is printed. The -v option causes a single word indicating the command or
file name used to invoke command to be displayed; the -V option produces a more verbose description. If the
-V or -v option is supplied, the exit status is 0 if command was found, and 1 if not. If neither option is
supplied and an error occurred or command cannot be found, the exit status is 127. Otherwise, the exit sta‐
tus of the command builtin is the exit status of command.
Spark shell 脚本中使用
判断是否已经安装了java