Скачать или смотреть 114 - Infinite Loops and Sleeping

In shell scripting, an infinite loop is a loop that continues to execute indefinitely, typically until explicitly terminated by the user or by some condition within the script. Infinite loops can be useful for tasks that need to run continuously, such as monitoring system status or waiting for user input.

Infinite Loop
Syntax
An infinite loop can be created using various constructs, such as while, for, or until. Here are a couple of common examples:

Using while
bash
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#!/bin/bash

while true; do
echo "This will run indefinitely."
You can add commands here
done
Using for
bash
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#!/bin/bash

for (( ; ; )); do
echo "This will also run indefinitely."
Add commands here
done
Using until
bash
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#!/bin/bash

until false; do
echo "This will run indefinitely."
Add commands here
done
Sleeping in Loops
To prevent an infinite loop from consuming too much CPU and to make it more manageable, you can use the sleep command. The sleep command pauses the execution of the script for a specified duration, which can be helpful in many scenarios, such as waiting for a resource to become available or reducing the frequency of checks in a monitoring script.

Syntax
The sleep command can take an argument specifying the number of seconds to sleep. It can also accept fractional values for more precise timing.

bash
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sleep 1 # Sleep for 1 second
sleep 0.5 # Sleep for half a second
Example of an Infinite Loop with Sleep
Here’s an example of an infinite loop that checks the system's disk usage every 10 seconds:

bash
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#!/bin/bash

while true; do
echo "Checking disk usage..."
df -h # Display disk usage
sleep 10 # Wait for 10 seconds before the next check
done
Key Points
Purpose: Infinite loops are useful for ongoing tasks but can lead to high CPU usage if not managed properly.
Control: To exit an infinite loop, you typically use a keyboard interrupt (like Ctrl+C) or implement an exit condition in the script.
Use of Sleep: Incorporating sleep helps manage resource usage and makes loops more practical, especially in monitoring or repetitive tasks.
Using infinite loops with proper controls and sleep intervals allows for efficient scripting, especially in long-running processes or monitoring tasks.