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copied!<p>As is mentioned elsewhere, regular expressions almost certanily not what you want. But, having said that, if you really want a regular expression, here is how it is built:</p> <p>31 day months </p> <pre><code>(0[13578]|1[02])[\/.](0[1-9]|[12][0-9]|3[01])[\/.](18|19|20)[0-9]{2} </code></pre> <p>30 day months</p> <pre><code>(0[469]|11)[\/.](0[1-9]|[12][0-9]|30)[\/.](18|19|20)[0-9]{2} </code></pre> <p>February 1-28 always valid</p> <pre><code>(02)[\/.](0[1-9]|1[0-9]|2[0-8])[\/.](18|19|20)[0-9]{2} </code></pre> <p>February 29 also valid on leap years</p> <pre><code>(02)[\/.]29[\/.](((18|19|20)(04|08|[2468][048]|[13579][26]))|2000) </code></pre> <p>which means it would be this if you put it all together:</p> <pre><code>((0[13578]|1[02])[\/.](0[1-9]|[12][0-9]|3[01])[\/.](18|19|20)[0-9]{2})|((0[469]|11)[\/.](0[1-9]|[12][0-9]|30)[\/.](18|19|20)[0-9]{2})|((02)[\/.](0[1-9]|1[0-9]|2[0-8])[\/.](18|19|20)[0-9]{2})|((02)[\/.]29[\/.](((18|19|20)(04|08|[2468][048]|[13579][26]))|2000)) </code></pre> <p>This version is a little shorter, but a little harder to understand.</p> <pre><code>((0[13578]|1[02])[\/.]31[\/.](18|19|20)[0-9]{2})|((01|0[3-9]|1[1-2])[\/.](29|30)[\/.](18|19|20)[0-9]{2})|((0[1-9]|1[0-2])[\/.](0[1-9]|1[0-9]|2[0-8])[\/.](18|19|20)[0-9]{2})|((02)[\/.]29[\/.](((18|19|20)(04|08|[2468][048]|[13579][26]))|2000)) </code></pre> <p>These scripts are long and unmaintainable. It should be clear that this isn't a good idea, but it is possible.</p> <p>Caveats:</p> <ul> <li>range 1800-2099 (more can be added without too much difficulty, but requires changes in 4-6 disparate places)</li> <li>requires 2 digit months and days (the strictness could be removed from the expression in ~8 places)</li> <li><code>[\/.]</code> as seperators (8 places)</li> <li>Hasn't been tested (we could check it against all digit combinations and compare with the javascript date function? [proof that we're reinventing the wheel])</li> </ul>

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