PATH环境变量也有缓存

hash - hash database access method

hase 命令：用来显示和清除哈希表，执行命令的时候，系统将先查询哈希表。

当你输入命令，首先在hash表中寻找，如果不存在，才会利用$PATH环境变量指定的路径寻找命令，然后加以执行。同时也会将其放入到hash table 中，当下一次执行同样的命令时就不会再通过$PATH寻找。以此提高命令的执行效率。

显示哈希表中命令使用频率

$ hash
hits	command
   6	/usr/bin/svn
   1	/bin/chown
   3	/bin/bash
   4	/usr/bin/git
  12	/usr/bin/php
   1	/bin/rm
   1	/bin/chmod
   1	/usr/bin/nmap
   5	/bin/cat
  13	/usr/bin/vim
   3	/usr/bin/sudo
   4	/bin/sed
   2	/bin/ps
   2	/usr/bin/man
  23	/bin/ls

显示哈希表

$ hash -l
builtin hash -p /usr/bin/svn svn
builtin hash -p /bin/chown chown
builtin hash -p /bin/bash bash
builtin hash -p /usr/bin/git git
builtin hash -p /usr/bin/php php
builtin hash -p /bin/rm rm
builtin hash -p /bin/chmod chmod
builtin hash -p /usr/bin/nmap nmap
builtin hash -p /bin/cat cat
builtin hash -p /usr/bin/vim vim
builtin hash -p /usr/bin/sudo sudo
builtin hash -p /bin/sed sed
builtin hash -p /bin/ps ps
builtin hash -p /usr/bin/man man
builtin hash -p /bin/ls ls

显示命令的完整路径

$ hash -t git
/usr/bin/git

向哈希表中增加内容

$ hash -p /home/www/deployment/run run

$ run
Usage: /home/www/deployment/run [OPTION] <server-id> <directory/timepoint>

OPTION:
	development <domain> <host>
	testing <domain> <host>
	production <domain> <host>

	branch {development|testing|production} <domain> <host> <branchname>
	revert {development|testing|production} <domain> <host> <revision>
	backup <domain> <host> <directory>
	release <domain> <host> <tags> <message>

	list
	list <domain> <host>

	clean {development|testing|production} <domain> <host>
	log <project> <line>

	conf list
	cron show
	cron setup
	cron edit

命令等同于

PATH=$PATH:$HOME/www/deployment

export PATH

删除哈希表内容

$ hash -r

$ hash -l
hash: hash table empty