Shell's While loop

The format of the while loop:

 while expression  Do Commandcommand 、、、  Done

1. Counter-controlled while loop:
Used primarily for the number of data and strings that have been accurately known to be entered.

Example:

#!/bin/bashint=1 while (($Int. <=5  )) do echo $int"int++" Done

2. End tag Control while loop
Mainly used to not know the number of read data, but you can set a special data value to end the loop, the special value is called the end tag, by prompting the user input to operate.

Example:

#!/bin/bash# using the end tag to control the while loop implementation guess 1~number within 10Echo "Please input the num (1~~10):"Read num while[[$num! =4 ]] Doif[$num-lt4]; Then  Echo "Too small,try again."Read numelif[$num-GT4]; Then  Echo "Too big,try again."Read numElseExit0fi DoneEcho "yes,you is right!"   

3. Flag-controlled while loop
User input flag value to control the end of the loop

Example:

#!/bin/BashEcho "Please input the num:"Read numsum=0I=1Signal=0# while[[$signal! =1 ]] while($signal! =1)) Doif[$i-eq $num]; Then Let"signal=1" Let"sum+=i"  Echo "1+2 、、、 + $num = $sum"Else Let"Sum=sum+i" Let"i++"fi Done

4. Command-line controlled while loop
Example:

#!/bin/bashecho"echo "  while""  ]"doesecho $1shift done

Shell's While loop