While loop instance in shell

shell Medium while Examples of loops _wdz306ling The blog of -CSDN Blog _shell while

1. utilize while Cycle calculation 1 To 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 To 100 The sum of all the odd numbers

#!/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 To 100 The sum of all the even numbers

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

echo $sum

2. utilize while Loop printing **

Sample code ： utilize while Print a loop 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 read text file ：

Sample code 1：

#!/bin/bash
file=$1                  # Set the position parameter 1 Copy the file name of to file
if [ $# -lt 1 ];then      # Judge whether the user has entered the position parameter
  echo "Usage:$0 filepath"
  exit
fi
while read -r line   # from file Read the file content in the file and assign it to line（ Using parameter r Will mask special symbols in the text , Only output, no translation ）
do

  echo $line        # Output file content

done   <  $file

Example 2： Read the contents of the file 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 The dead circle in the circle ：

Example ： Using the dead loop , Let the user make a choice , Print the corresponding 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
# Do the corresponding operation according to the customer's choice
  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    # Suspension loop , Prompt the customer to press enter Key continuation
    ;;
   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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