Linux Shell???????25??

????Q:19 ??shell????У????д????? ?
??????????????????????????????????????????ι???????????????#????????????￡?
????#!/bin/bash
????# This is a command
????echo “I am logged in as $USER”
????Q:20 ????? shell ???????????????????
??????read???????????????????ü???????????read??????????????????????????????С????????￡?
????# vi /tmp/test.sh
????#!/bin/bash
????echo ‘Please enter your name’
????read name
????echo “My Name is $name”
????# ./test.sh
????Please enter your name
????LinuxTechi
????My Name is LinuxTechi
????Q:21 ?????????????????????? ?
??????“unset”????????????????????????????????????????
????# unset <Name_of_Variable>
????Q:22 ?????????????? ?
????????????????????????????
???????expr????# expr 5 + 2?? 2.???????????????????$[ ???? ]?????磺test=$[16 + 4] ; test=$[16 + 4]
????Q:23 do-while?????????? ?
??????do-while?????????while??????????????????????????LCTT ????????????????Ρ?????????????do-while??????
????do
????{
????statements
????} while (condition)
????Q:24 ??shell?????ζ??庯???? ?
???????????????????????顣????????????飬???????????????????ú??????????????С?????????????
????$ diskusage () { df -h ; }
????Q:25 ?????shell????????BC??bash???????? ?
????????????и??????shell????????bc??
????variable=`echo “options; expression” | bc`