手记05之linux查看命令是否为内建命令(type)

type [ - aftpP] name [ name . . . ]

      With no options, indicate how each name would be interpreted if used as a command name.

   If the - t option is used, type prints a string which is one of alias, keyword, function, builtin, or file if name is an alias, shell reserved word, function, builtin, or disk file, respectively. If the name is not found, then nothing is printed, and an exit status of false is returned.

    If the - p option is used, type either returns the name of the disk file that would be executed if name were specified as a command name, or nothing if ‘‘type - t name’’ would not return file. The - P option forces a PATH search for each name, even if ‘‘type - t name’’ would not return file. If a command is hashed, - p and - P print the hashed value, not necessarily the file that appears first in PATH.

     If the - a option is used, type prints all of the places that contain an executable named name. This includes aliases and functions, if and only if the - p option is not also used. The table of hashed commands is not consulted when using - a. The - f option suppresses shell function lookup, as with the command builtin.

    type returns true if any of the arguments are found, false if none are found.

eg:

[root@localhost Desktop]# type -a ls

ls is aliased to `ls --color=tty'

ls is /bin/ls

[root@localhost Desktop]# type -a type

type is a shell builtin