計數器篇：對輸入的數字進行判斷並計算

確認是否要改變COUNTER的值。如果輸入Y或者y，則繼續輸入要累加的數字，輸入非法數字或者未輸入則直接退出程序，輸入正常數字則計算累加到COUNTER；輸入Y或者y以外的值則退出程序。

#!/bin/bash
COUNTER=100
echo -n "Do you want to change your $COUNTER?[Y or N]:"
read ANS
if [ "$ANS" = "Y" ] || [ "$ANS" = "y" ] ; then
 echo  "Please enter your number:"
 read VALUE
 expr $VALUE + 10 >/dev/null 2>&1
 if [ $? != 0 ] || [ $VALUE = "" ] ;then
  echo "You enter illegal digit!"
  exit 1
 fi
 COUNTER=`expr $COUNTER + $VALUE`
 echo "The new COUNTER is $COUNTER !"
else
 echo "I don't wish to change COUNTERS."
 exit 1
fi

[root@localhost home]# ./ifcounter.sh 
Do you want to change your 100?[Y or N]:N
I don't wish to change COUNTERS.
[root@localhost home]# ./ifcounter.sh 
Do you want to change your 100?[Y or N]:y
Please enter your number:
ssd
You enter illegal digit!
[root@localhost home]# ./ifcounter.sh 
Do you want to change your 100?[Y or N]:Y
Please enter your number:
3
The new COUNTER is 103 !

 

注意點：if [ "$ANS" = "Y" ] || [ "$ANS" = "y" ]，中括號前後要有空格，=號前後也要有空格

 

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