Regular Expression - Only number from X to Y [duplicate]

This question already has answers here: 开发者_如何转开发 Closed 11 years ago.

Possible Duplicate:

Regular expression where part of string must be number between 0-100

I'd like to know how to filter a variable that must be only numbers and from 1 to 300 by using regular expression on PHP. How can I do it?

P.S. I can't really find a good manual with definition of each symbol about regex. For example, what does it mean /^ or +$/i??

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([1-9][0-9]?|[12][0-9][0-9]|300)

In other words, either (|) match a number from 1 to 9 ([1-9]), from 10 to 99 ([1-9][0-9]?), from 100 to 299 ([12][0-9][0-9]), or 300.

See:

• Regular Expressions Reference - Basic Syntax
• Regex Tutorial - Start of String and End of String Anchors

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Don't do that -- this can become overly complicated. Just break out the number from the string, convert it to integer (if you like to) and check its value:

function match( $n ) {
  preg_match( '(\d+)', $n, $matches );
  return $matches && $matches[ 0 ] >= 1 && $matches[ 0 ] <= 300;
}