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Rejecting certain regex patterns

I am new to regex and am trying to match a string that

  • may be long
  • may be alphanumeric and may also contain $

    , -

    or/

  • cannot contain more than two of these non-alphanumeric characters in a string or end with /

    or -

    .

For example, Hello/World

is valid, Hello//World

is invalid.

I've tried a couple of different possibilities, with this one getting closer to working as I expect:

^--|-/|/-|\s\s|$$|$-|-$|$/|/$|//|([a-zA-Z0-9 -$/])*(?<![/-])$

This seems to be sufficient for every scenario, except when the two forward slashes are together. Do I need to escape the leading slashes, or is it because my matching expression is too large and swallowing bad lines? I've tried different expressions with negative look and feel, but they all run into problems, especially with false negatives.

Greetings,

Jeff

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2 answers


Here's the regex you're looking for:

^(?![^/$-]*[/$-]{2})[\w/$-]+(?<![/-])$

Regex Demo and IDEONE Java Demo



String str1 = "Hello/World";
String str2 = "Hello//World";
String ptrn = "^(?![^/$-]*[/$-]{2})[\\w/$-]+(?<![/-])$";
System.out.println(str1.matches(ptrn)); // => true
System.out.println(str2.matches(ptrn)); // => false

Explanation:

  • ^

    - beginning of line (optional in matches()

    )
  • (?![^/$-]*[/$-]{2})

    - Lookahead ensuring that the string contains at most 1 non-alphanumeric character
  • [\w/$-]+

    - the class of the base character corresponding to the alphanumeric characters and /

    , $

    or-

  • (?<![/-])

    - Make sure the string does not end with prohibited non-alphanumeric characters.
  • $

    - End of line (optional in matches()

    )
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You were on the right track with negative imagery, you just needed to include a capture group link.

^([^\$-\/]|([\$-\/])(?!\2))+?[^\/-]$



This regex will fail for any $, -, or / it captures. It also has a lazy quantifier to make sure it doesn't override the end / or - check.

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