How to Restrict Character Length in a Regular Expression?

Restricting Character Length in a Regular Expression

When using regular expressions to match particular patterns in strings, it is often necessary to restrict the character length to ensure accurate matching. In the provided example:

var test =  /^(a-z|A-Z|0-9)*[^$%^&*;:,<>()?""']*$/

This regex matches any string consisting of letters or digits without any restricted character length. An attempt to restrict the character length to 15 using [^$%^&*;:,<>()?""']*${1,15} results in an error.

To resolve this issue and enforce a character limit, use a lookahead anchored at the beginning of the string:

^(?=.{1,15}$)...

This lookahead checks if the string matches 1 to 15 characters but excludes the newline at the end (due to $). It restricts the length of the entire input string.

Using a quantifier at the end, such as [^$%^&*;:,<>()?""']{1,15}, will only restrict the length of the second character class, not the whole string.

For strings that may contain a newline sequence, use [sS] to match any character:

^(?=.[\s\S]{1,15}$)...

This ensures that the character length restriction applies across the entire string, regardless of newlines.

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