Shell script Programming loop control statement (CONTINUE/BREAK/SLEEP)

Loop Control statement:

Continue: End this cycle prematurely, and go directly to the next round of cycle judgment;

While CONDITION1; Do

CMD1

...

if CONDITION2; Then

Continue

Fi

Cmdn

...

Done

Example: The sum of all even numbers within 100;

#!/bin/bash
#
declare -i evensum=0
declare -i i=0
while [ $i -le 100 ]; do
    let i++
    if [ $[$i%2] -eq 1 ]; then
        continue
    fi
    let evensum+=$i
done
echo "Even sum: $evensum"

Break: Jump out of circulation early

While CONDITION1; Do

CMD1

...

if CONDITION2; Then

Break

Fi

Done

To create a dead loop:

While true; Do

Loop body

Done

Exit Method:

When a test condition is satisfied, let the loop body execute the break command;

Example: The sum of the odd numbers within 100

#!/bin/bash
#
declare -i oddsum=0
declare -i i=1
while true; do
    let oddsum+=$i
    let i+=2
    if [ $i -gt 100 ]; then
        break
    fi
done

Sleep command:

-Delay for a specified amount of time

Sleep Number

Exercise: Every 3 seconds to the system to obtain the user's logged on user information, where if the Logstash user logged in the system, the log is logged, and exit;

#! / bin / bash
#
while true; do
     if who | grep "^ logstash \>" &> / dev / null; then
         break
     fi
sleep 3
done
echo "$ (date +"% F% T ") logstash logged on" >> /tmp/users.log

Use untill
#! / bin / bash
#
until who | grep "^ logstash \>" &> / dev / null; do
sleep 3
done
echo "$ (date +"% F% T ") logstash logged on" >> /tmp/users.log 

This article is from the "Wang Liming" blog, make sure to keep this source http://afterdawn.blog.51cto.com/7503144/1916025

Shell script Programming loop control statement (CONTINUE/BREAK/SLEEP)