Regex expression to bold using asterisks-CodePudding

I have a question regarding using a regular expression to bold text within a string using asterisks.

The other questions on this topic work well for simple scenarios however we have encountered some issues.

Our particular scenario is for asterisks to be replaced with <bold></bold> tags. It must also be able to handle multiple asterisks as well as an uneven number of asterisks.

Our example input text is as follows;

string exampleText1 = "**** PLEASE NOTE *** Testing, *nuts*, **please note..., test";

string exampleText2 = "**Test text (10)";

Our current regex is as follows;

Regex _boldRegex = new Regex(@"(\*) ([^*?$] ) (\*)");

string value = _boldRegex.Replace(exampleText1, @"<bold>$2</bold>");

Example 1 should show "<bold> PLEASE NOTE </bold> Testing, <bold>nuts</bold>, *please note..., test" where the groups of asterisks are treated as single asterisks and an unfinished tag is ignored.

Example 2 crashes the program because it expects a 'closing' asterisk. It should show "*Text text (10)"

Can anyone help by suggesting a new regex, bearing in mind the ability to handle groups of asterisks and also an uneven number of asterisks?

Thanks in advance.

CodePudding user response：

For you examle data, you might use an optional part with a capture group to capture the repeated character class without newlines between 1 or more *

In the callback of replace, you can test for the existence of group 1, and do the replacements based on that.

\* (?:([^*?$\n\r] )\* )?

The pattern matches:

\* Match 1 times *
(?: Non capture group
- ( Capture group 1
  - [^*?$\n\r] Match 1 times any char other than the listed in the character class
- ) Close group 1
- \* Match 1 times *
)? Close on capture group

See a regex demo.

For example

Regex _boldRegex  = new Regex(@"\* (?:([^*?$\n\r] )\* )?");
string exampleText1 = @"**** PLEASE NOTE *** Testing, *nuts*, **please note..., test
**Test text (10)";
string value = _boldRegex.Replace(exampleText1, m => 
    m.Groups[1].Success ? String.Format("<bold>{0}</bold>", m.Groups[1].Value) : "*"
);
Console.WriteLine(value);

Output

<bold> PLEASE NOTE </bold> Testing, <bold>nuts</bold>, *please note..., test
*Test text (10)