Questions about input verification in PHP

For the first time I used PHP for input verification in PHP, I used PHP as an online bookstore. during background management, the administrator entered the basic information of the book in the HTML form, how can I verify the input information. For example, the number of pages in a book must be an integer, but an error may occur when you enter text or other words. I want to use a regular expression, but I don't know how to write it ., JavaScript can solve the input verification problem in PHP.
For the first time, I used PHP as an online bookstore. during background management, the administrator entered the basic information of the book in the HTML form. how can I verify the input information. For example, the number of pages in a book must be an integer, but an error may occur when you enter text or other words. I want to use a regular expression, but I don't know how to write it.

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Js.
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Verify the JavaScript code once and submit the php page again.
If (isnumeric (number submitted ))
{
........
}
Else
Echo 'error occurred ';
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Use regular expression to judge js
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The next upstairs program.

If (is_int (submitted numeric variable )){
........
}
Else
Echo 'error occurred ';

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I will not learn about JS.
How can I do this without learning?