????????? bash shell ??????????????? bash shell ???????????????????????? unset ????????????????????????????? bash ?? ksh shell ??????????????г??????
??????????? Linux ???? Unix ??????? env ???????ò??????????env ???????????????????????????????????????г???

???????????????????
???????????ó???????????????????????
????printenv
??????
????env
?????????????

????Fig.01?? Unix/Linux?? ?г????л???????
?????????????????
?????????????????
????env | wc -l
????printenv | wc -l    # ????
?????????????
????20
?????????? bash/ksh/zsh ?????????г???
???????????????
????env -i your-program-name-here arg1 arg2 ...
???????磬??????? http_proxy ??/???κ???????????????????????? wget ?????????????? bash/ksh/zsh ?????????????? wget ????
????env -i /usr/local/bin/wget www.cyberciti.biz
????env -i wget www.cyberciti.biz     # ????
??????????????κ?????????????????????????????????á?????????????????????????? http_proxy ??????????????????????
???????????? http_proxy
????$ wget www.cyberciti.biz
????--2015-08-03 23:20:23--  http://www.cyberciti.biz/
????Connecting to 10.12.249.194:3128... connected.
????Proxy request sent?? awaiting response... 200 OK
????Length: unspecified [text/html]
????Saving to: 'index.html'
????index.html                 [  <=>                         ]  36.17K  87.0KB/s   in 0.4s
????2015-08-03 23:20:24 (87.0 KB/s) - 'index.html' saved [37041]
????????????? http_proxy
????$ env -i /usr/local/bin/wget www.cyberciti.biz
????--2015-08-03 23:25:17--  http://www.cyberciti.biz/
????Resolving www.cyberciti.biz... 74.86.144.194
????Connecting to www.cyberciti.biz|74.86.144.194|:80... connected.
????HTTP request sent?? awaiting response... 200 OK
????Length: unspecified [text/html]
????Saving to: 'index.html.1'
????index.html.1               [  <=>                         ]  36.17K   115KB/s   in 0.3s
????2015-08-03 23:25:18 (115 KB/s) - 'index.html.1' saved [37041]
????-i ???? env ???????????????е????????????????????????????????? wget ?? curl???????μ??????????????????? bash/ksh shell ????????
????env -i env | wc -l ## ??? ##
????# ???????? bash ##
????env -i bash
????## bash ???????μ???????? ##
????env | wc -l
????????????????????????
?????????￡?
????env var=value /path/to/command arg1 arg2 ...
????## ?? ##
????var=value  /path/to/command arg1 arg2 ...
???????????? http_proxy:
????env http_proxy="http://USER:PASSWORD@server1.cyberciti.biz:3128/" /usr/local/bin/wget www.cyberciti.biz