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Editorial Team
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Asked: 2026-06-06T00:11:05+00:00

I have a problem with regards to writing the correct regex for the examination

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I have a problem with regards to writing the correct regex for the examination rating field of my grails application. Users should have the option to either enter an alphabet character OR a number. Quantitative rating should range from 0-100, accepts decimal numbers with or without percentage sign (%) but exclude negative numbers. The regex should permit special characters percentage(%) and period (.) ONLY. Below is a set of possible input:

1) 100% (should pass the validation)
2) 100.0 (should pass the validation)
3) PASSED (should pass the validation)
4) FAILED (should pass the validation)
5) 100.1 (should not pass the validation)
6) -90 (should not pass the validation)

Your answer will be highly appreciated.

Thanks!

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1 Answer

  1. Editorial Team

    I assume the language is Java. I also assume that you want to validate user input, which expects to contain only the percentage.

    "^\\s*((100(\\.0*)?|\\d{1,2}(\\.\\d*)?|\\.\\d+)%?|PASSED|FAILED)\\s*$"

    (In Groovy, you don’t have to escape the backslash)

    /^\s*((100(\.0*)?|\d{1,2}(\.\d*)?|\.\d+)%?|PASSED|FAILED)\s*$/ (for Groovy)

    The regex above will only validate numbers between 0.0 to 100.0. It allows arbitrary long number of digits after decimal points, and also allows cases such as .8 or 45. to pass, since they can be processed. The regex also allows any amount of spaces before and after the input (but not inside).

    EDIT

    To match plain text (ASCII):

    "^\\s*((100(\\.0*)?|\\d{1,2}(\\.\\d*)?|\\.\\d+)%?|[a-zA-Z.]+)\\s*$"

/^\s*((100(\.0*)?|\d{1,2}(\.\d*)?|\.\d+)%?|[a-zA-Z.]+)\s*$/ (for Groovy)

    This will match text that uses English alphabet character (case-insensitive), and full-period. E.g. sdhSDFHS.sfSDJF.sdfSDJFI will matches the above regex. Note that the current regex does not allow spaces within the text, but if you want to add more characters, add inside the square bracket (character class): [a-zA-Z.]. Check the documentation for more details.

    Testing code (for Java)

    String arr[] = {"100%", "  .435%", "3%", "0%", "0", ".0", "hdfjs.", "  PASSED", "FAILED", "34.5  ", "sdhf.sdfdsf.fsdf  ", " 100.0000 ", "-234.4", "-0.1", "34.", "100.0000001", "1000"};
for (String s: arr) 
    System.out.println(s + " " + (s.matches("^\\s*((100(\\.0*)?|\\d{1,2}(\\.\\d*)?|\\.\\d+)%?|[a-zA-Z.]+)\\s*$") ? "matched" : "not matched"));

    Output

    100% matched
  .435% matched
3% matched
0% matched
0 matched
.0 matched
hdfjs. matched
  PASSED matched
FAILED matched
34.5   matched
sdhf.sdfdsf.fsdf   matched
 100.0000  matched
-234.4 not matched
-0.1 not matched
34. matched
100.0000001 not matched
1000 not matched

    EDIT2

    Change in requirement as mentioned in the discussion: only match from 1.0 to 100.0 inclusive for the percentage:

    /^\s*((100(\.0*)?|[1-9]\d?(\.\d*)?)%?|[a-zA-Z.]+)\s*$/ (for Groovy)

    This condition is even more stricter than before, since 01.1 will not match. If you want to match this case:

    /^\s*(0*((100(\.0*)?|[1-9]\d?(\.\d*)?)%?)|[a-zA-Z.]+)\s*$/ (for Groovy)
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