????????
????Linux?????????????????????????????????????????????????????????????乤??????????????????????????????????????
?????????????????????
??????????????????shell??????????????а????????Щ??????linux????????Щ??????shell?????????shell?????????????У??????linux???????????shell??????????????????С??????????д??bashy???????????????????????????????????????shell??????????????????磺exit??history??cd??echo???
???????????????????е????????????????????????????С?
??????????????
????????????linux???е???ó???????????ó?????????????????????????????????????????????????????????????????????С??????????????????????檔????????????岢????????shell?У?????????????й???????shell?????????shell???????????????е?·???????????????????????????С???????????bash?????????????????/bin??/usr/bin??/sbin??/usr/sbin……?????????“echo $PATH”????????????洢·???????磺ls??vi???
?????????????????????????????????
????1????????????
?????ж????????????????????????????????type command
[root@localhoast ~]# type pwd
pwd is a shell builtin
[root@localhoast ~]# type vim
vim is /usr/bin/vi
?????????builtin?????????????????????????????????·???????????????
????2?????????й???
????????????????????????????????????????????????????е???????????????????????.bash_profile??/etc/profile???PATH·????
?????????????????????????Щ????????ù??????????hash???У???????????????????????????????????????
????hash——>????????——>PATH   ????????????????????????????hash???????????????????????????????
[root@localhost ~]# pwd
/root
[root@localhost ~]# ls
anaconda-ks.cfg  install.log  install.log.syslog
[root@localhost ~]# hash -l????//???hash??
builtin hash -p /bin/cat cat
builtin hash -p /bin/ls ls
??????hash???п????????hash???????????????