Specific use of Linux which command

Search for files in environment variables -a Search all contents instead of the first file -n <file name length> Specify the file name length. The specified length must be greater than or equal to the longest file name among all files. 
-p <filename length> is the same as the -n parameter, but the <filename length> here includes the file path. 
-w specifies the width of the output columns. 
-V Display version information.

--version, -[vV] show version information and exit --help show this help message and exit --skip-dot skip directories in PATH that begin with a dot --skip-tilde skip directories in PATH that begin with a tilde --show-dot do not expand dot to current directory in output --show-tilde print tilde for HOME directory (non-root) --tty-only if not on a tty, stop processing options to the right --all, -a print all matches in PATH, not just the first --read-alias, -i read alias list from stdin --skip-alias ignore option --read-alias; do not read stdin
--read-functions Read shell functions from stdin --skip-functions Ignore option --read-functions; do not read stdin

[deng@localhost test]$ which bash
/usr/bin/bash

[deng@localhost test]$ which which
alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot --show-tilde'
    /usr/bin/alias
    /usr/bin/which
[deng@localhost test]$ 

[deng@localhost test]$ which pwd
/usr/bin/pwd

[root@localhost ~]# which pwd
/bin/pwd
[root@localhost ~]#

[root@localhost ~]# which type
/usr/bin/which: no type in (/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin)
[root@localhost ~]#