Php time timer

For the php time timer, please help me. how does php get the time timer, that is, execute the program at intervals ?, PHP doesn't seem to exist. it should be in JS or in linux/unix !, Use sleep () to set the interval and run the program as a command line ., The simplest way is to judge the php time timer in the code.
Please help me. how can I get a time timer for php? that is to say, I want to execute the program at intervals?

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PHP doesn't seem to have any,
It should be in JS or in linux/unix!
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Use sleep () to set the interval and run the program as a command line.
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The simplest way is to judge the time in the code and run it at that time. For static pages, you can use javascript src = 'XXX. php' to start them. The premise is that a visitor cannot run without a visitor.
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You can write a scheduled task, but you can run Windows linux, and then decide at what time.
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1. you can use for and add a sleep
2. or make a scheduled task in win.
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Find out the web principles before posting.
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Well, use the sleep function .~~~~~~~~
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This is a very unrealistic problem. Or ajax or system scheduled tasks. Sleep makes PHP always have a process, and it feels uncomfortable.
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Cronjob
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It is best to do this in windows or linux.
If it is a rented host, it cannot be done.
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PHP
Look at commet technology
Loop + sleep ()

JS
SeTimeout ();