Question 245836 in Javascript Question posted in
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Javascript regex expression for underscore

I have a input field in GUI where user enters a text in textbox and clicks Save. I have to validate that text/string for below pattern.

String: "--cpuname=some_text" // Invalid string, underscore not allowed
String: "--cpuname=$(some_text)" // Valid string
String: "--cpuname=$(some_text) -order=abc_def" //Valid string

if cpuname value has underscore in it , then its not valid. But underscore is allowed if it is between $( and ) like the second example above. Note: --cpuname might not be starting of the string always and other part of text can have underscores.(except cpuname value)

Hope my requirement is clear. I have tried to take help of ChatGPT but quite dint succeed.

The code I tried :

const regex = /--cpuname=[$(][^)]+)|--cpuname=[^_]+(?:s-w+=w+)*$/;

function checkStringValidity(str) {
  if (!regex.test(str)) {
    alert("Underscore not allowed");
  }
}
Tags:

2

Answers


  1. 0

    If the value has an underscore and it’s not enclosed between $( and ), it’s invalid.
    If the value is enclosed between $( and ), underscores are allowed.
    Let’s break down the problem:

    We need to find –cpuname= followed by a value.
    The value can be:
    Enclosed between $( and ) and can contain any character.
    Not enclosed and should not contain an underscore.
    Let’s write a regex for this:

    –cpuname=$([^)]+): This matches –cpuname=$(some_text).
    –cpuname=[^_s]+: This matches –cpuname=someText but not –cpuname=some_text.
    Combining these two with an OR | operator should give us the desired regex.

    Here’s the updated code:

    const regex = /--cpuname=($([^)]+)|[^_s]+)/;

function checkStringValidity(str) {
  const matches = str.match(regex);
  if (!matches || matches[0] !== matches.input) {
    alert("Underscore not allowed in cpuname value");
    return false;
  }
  return true;
}

    Let’s test this with your examples:

    –cpuname=some_text should be invalid.

    –cpuname=$(some_text) should be valid.

    –cpuname=$(some_text) -order=abc_def should be valid.

    Login or Signup to reply.
  2. 0

    I’d suggest a different logic: create a regex that will match invalid --cpuname values and if there is a match, trigger an alert.

    const regex = /--cpuname=(?:$([^()]*)|(?!$()[^_s])*_/;

function checkStringValidity(str) {
  return regex.test(str);
}

const strs = ["--cpuname=some_text","--cpuname=$(some_text)", "--cpuname=$(some_text) -order=abc_def"];
for (const str of strs) {
  if (checkStringValidity(str)) {
    console.log("Underscore not allowed in cpuname value" + "nThe '" + str + "' string is invalid!");
  } else {
    console.log("The '" + str + "' string is valid!");
  }
}

    See the regex demo.

    Details:

    • --cpuname= – a literal text
    • (?:$([^()]*)|(?!$()[^_s])* – a non-capturing group that matches – 0 or more times – either of
      • $([^()]*) – a $( + any zero or more chars other than ( and ) + )
      • | – or
      • (?!$()[^_s] – a char other than _ and whitespace that does not start a $( char sequence
    • _ – an underscore.
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