1. whereis ：显示指令的二进制程序、源代码文件和man手册的路径
1.1 查找所有信息
~$ whereis emacs emacs: /usr/bin/emacs /etc/emacs /usr/lib/emacs /usr/bin/X11/emacs
/usr/share/emacs /usr/share/man/man1/emacs.1.gz
1.2 仅查找二进制程序
$ whereis -b emacs emacs: /usr/bin/emacs /etc/emacs /usr/lib/emacs /usr/bin/X11/emacs
/usr/share/emacs
1.3 仅查找源代码文件
~$ whereis -s emacs
emacs:
1.4 仅查找man手册页
~$ whereis -m emacs emacs: /usr/share/man/man1/emacs.1.gz
2. which : 仅显示指令的绝对路径
和whereis不同的是，which只能显示指令的绝对路径。
3. locate/slocate ：快速定位文件的路径
locate指令利用事先建立的系统中左右文件名称及路径的数据库，从而实现快速定位。如果该数据库比较陈旧，使用updatedb即可更新。
和whereis以及which相比，locate可以查找普通文件，只要是带有搜索关键字的都会输出，因此内容会比较多。
3.1 输出符合条件的文件总数
~$ locate -c
emacs 3737
3.2 输出所有匹配条目
~$ locate emacs
/usr/share/emacs23/site-lisp/flim/mmgeneric.elc
/usr/share/emacs23/site-lisp/flim/ntlm.el
/usr/share/emacs23/site-lisp/flim/ntlm.elc
/usr/share/emacs23/site-lisp/flim/qmtp.el
/usr/share/emacs23/site-lisp/flim/qmtp.elc
/usr/share/emacs23/site-lisp/flim/sasl-cram.el
/usr/share/emacs23/site-lisp/flim/sasl-cram.elc
/usr/share/emacs23/site-lisp/flim/sasl-digest.el
/usr/share/emacs23/site-lisp/flim/sasl-digest.elc
/usr/share/emacs23/site-lisp/flim/sasl-ntlm.el
/usr/share/emacs23/site-lisp/flim/sasl-ntlm.elc
/usr/share/emacs23/site-lisp/flim/sasl-scram.el
/usr/share/emacs23/site-lisp/flim/sasl-scram.elc
/usr/share/emacs23/site-lisp/flim/sasl.el
/usr/share/emacs23/site-lisp/flim/sasl.elc
/usr/share/emacs23/site-lisp/flim/sha1-dl.el
/usr/share/emacs23/site-lisp/flim/sha1-dl.elc
/usr/share/emacs23/site-lisp/flim/sha1-el.el
/usr/share/emacs23/site-lisp/flim/sha1-el.elc
/usr/share/emacs23/site-lisp/flim/sha1.el
/usr/share/emacs23/site-lisp/flim/sha1.elc
/usr/share/emacs23/site-lisp/w3m/shimbun/sb-atmarkit.el
/usr/share/emacs23/site-lisp/w3m/shimbun/sb-atmarkit.elc
........
/var/lib/dpkg/info/emacsen-common.list /var/lib/dpkg/info/emacsen-common.postinst /var/lib/dpkg/info/emacsen-common.postrm /var/lib/dpkg/info/emacsen-common.prerm /var/lib/emacsen-common/installed-flavors