shell script loop

And from 1 to the request 100

Using a for loop summation:

#!/bin/bash

declare -i sum=0

for ((i=1;i<=100;i++));do

    let sum+=$i

done

echo "sum=$sum"

Use until the cycle summation:

#!/bin/bash

i=1

sum=0

until [ $i -gt 100 ];do

    let sum+=$i

    let i++

done

echo "sum is:$sum"

Use a while loop summation:

#!/bin/bash

i=1

sum=0

while [ $i -le 100 ];do

    let sum+=$i

    let i++

done

echo "sum is:$sum"

Seeking the sum of the even less than 100

Using a for loop summation:

#!/bin/bash

i=0

sum=0

for i in `seq 100` ;do

        if [ $[$i%2] -eq 1 ];then

        continue

    fi  

    let sum+=$i

done

echo "sum is:$sum"

Use a while loop summation:

#!/bin/bash

i=0

sum=0

while [ $i -le 100 ];do

    let i++

    if [ $[$i%2] -eq 1 ];then

        continue

    fi

    let sum+=$i

done

echo "sum is: $sum"

Use until the cycle summation:

#!/bin/bash

i=0

sum=0

until [ $i -gt 100 ];do

    let i++

    if [ $[ $i%2 ] -eq 1 ];then

        continue

    fi

    let sum+=$i

done

echo "sum is: $sum"

Writing a multiplication table

Using a for loop:

#!/bin/bash

#for i in `seq 9`;do

for ((j=1;j<=9;j++));do

    for ((i=1;i<=j;i++));do

        echo -ne "$i*$j=$(($i*$j))\t"

    done

    echo

done

Use a while loop:

#!/bin/bash

i=1

j=1

while[ $j -le 9 ];do

    while [ $i -le $j ];do

        echo -ne "$i*$j=$(($i*$j))\t"

        let i++

    done

    echo

    let i=1

    let j++

done

Use until the cycle:

#!/bin/bash

i=1

j=1

until [ $j -gt 9 ];do

    until [ $i -gt $j ];do

        echo -ne "$i*$j=$(($i*$j))\t"

        let i++

    done

    echo

    let i=1

    let j++

done

A script is determined whether the user login to the system, if not, the cycle once every 10 seconds

Use a while loop:

#!/bin/bash

read -p "pls input a username: " username

while ! `who |grep "^$username" &> /dev/null`;do

    sleep 10

done

echo "`date +%F-%H:%M:%S` $username logged on">>/tmp/user.log

Use case loop to obtain system information

#!/bin/bash

cat <<EOF

1) show cpu information;

2) show memory information;

3) show disk information;

4) quit

EOF

cpu_info(){

    lscpu

    }

mem_info(){

    cat /proc/meminfo

    }

disk_info(){

    fdisk -l

    }

quit(){

    echo "quit"

    exit 0

    }   

read -p "pls input a num: " num

if [ $num -ne 1 -a $num -ne 2 -a $num -ne 3 -a $num -ne 4 ];then 

    read -p "pls input a num again: " num

fi

case "$num" in 

1) 

    cpu_info

    ;;

2)

    mem_info

    ;;

3)

    disk_info

    ;;

4)

    quit

esac

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