As OG already answered: \d{10}
Just a few interesting links to help building and debugging RegEx.
Here is a link to RegEx documentation:
perlre - perldoc.perl.org[
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Here is links to tools to help build RegEx and debug them:
.NET Regex Tester - Regex Storm[
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Expresso Regular Expression Tool[
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RegExr: Learn, Build, & Test RegEx[
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Online regex tester and debugger: PHP, PCRE, Python, Golang and JavaScript[
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This one show you the RegEx as a nice graph which is really helpful to understand what is doing a RegEx:
Debuggex: Online visual regex tester. JavaScript, Python, and PCRE.[
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This site also show the Regex in a nice graph but can't test what match the RegEx:
Regexper[
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[Update]
If you read carefully the RegExs, you will see that
/^\d{10}$/ and
\d{10} are different and thus match different strings. Read documentation to understand what is the difference.