1. utilize while Cycle calculation 1 reach 100 And :

Sample code 1:

#!/bin/bash
i=1
sum=0
while [ $i -le 100 ]
do
  let sum=sum+$i
  let i++
done

echo $sum

Sample code 2: utilize while Cycle calculation 1 reach 100 The sum of all odd numbers between

#!/bin/bash
i=1
sum=0
while [ $i -le 100 ]
do
  let sum=sum+$i
  let i+=2
done

echo $sum

Sample code 3: utilize while Cycle calculation 1 reach 100 Sum of all even numbers between

#!/bin/bash
i=2
sum=0
while [ $i -le 100 ]
do
  let sum=sum+$i
  let i+=2
done

echo $sum

2. utilize while Circular printing **

Sample code : utilize while Cycle one 5x5 Of *

#!/bin/bash
i=1
j=1
while [  $i  -le  5  ]
do
  while [  $j  -le  5  ]
  do
     echo -n  "*  "
     let j++
  done
  echo
  let  i++
  let  j=1

done

3. use read combination while Loop through text file :

Sample code 1:

#!/bin/bash
file=$1                  # Position parameter 1 Copy the file name of to file
if [ $# -lt 1 ];then      # Determine whether the user has entered the location parameters
  echo "Usage:$0 filepath"
  exit
fi
while read -r line   # from file The read file content in the file is assigned to line( Using parameters r Special symbols in text will be masked , Only output, not translation )
do

  echo $line        # Output file content

done   <  $file

Examples 2: Read file contents by column

#!/bin/bash
file=$1
if [[ $# -lt 1 ]]
then
  echo "Usage: $0 please enter you filepath"
  exit
fi
while read -r  f1 f2 f3    # Divide the contents of the document into three columns
do
  echo "file 1:$f1 ===> file 2:$f2 ===> file 3:$f3"   # Output file contents by column

done < "$file"

4.while Dead loop in loop :

Examples : Using the dead cycle , Let users choose , Print the results according to the customer's choice

#!/bin/bash
# Print menu
while :
do
  echo "********************"
  echo "        menu        "
  echo "1.tima and date"
  echo "2.system info"
  echo "3.uesrs are doing"
  echo "4.exit"
  echo "********************"
  read -p "enter you choice [1-4]:" choice
# According to the customer's choice to do the corresponding operation
  case $choice in
   1)
    echo "today is `date +%Y-%m-%d`"
    echo "time is `date +%H:%M:%S`"
    read -p "press [enter] key to continue..." Key    # Pause the cycle , Prompt customer to press enter Key to continue
    ;;
   2)
    uname -r
    read -p "press [enter] key to continue..." Key
    ;;
   3)
    w
    read -p "press [enter] key to continue..." Key
    ;;
   4)
    echo "Bye!"
    exit 0
    ;;
   *)
    echo "error"
    read -p "press [enter] key to continue..." Key
    ;;
  esac

done

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