正则表达式匹配字符串中间的子字符串

Question

I need help completing a regex expression. I have the following regex: /(?i)encntr(?-i)/gi

https://regex101.com/r/t4pUkr/1/

I have the following three filenames:

• 20200207050000-20200207162558-encntr.txt - should match using encntr
• 20200207050000-20200207162558-encntrprov.txt - should NOT match using encntr
• 20200207050000-20200207162558-encntrlocation.txt - should NOT match using encntr

My above regex matches all 3 but I only want it to match the first bullet point. So I'm trying to use the ^(not) operator to achieve this but I'm not getting anywhere. Ignore the previous sentence, my understanding using ^ was ill-informed. Additionally it would be more robust if I could do this without depending on the - and . that encntr, encntrprov, and encntrlocation are wrapped in. I do not author the files and can't guarantee the author follows a naming convention. Thus I cannot not guarantee the - and . will always be there.

Example of possible other file names:

• 20200207050000-20200207162558encntr.txt - should match using encntr
• 20200207050000-20200207162558encntr01.txt - should match using encntr
• 20200207050000-20200207162558_encntr_.txt - should match using encntr
• 20200207050000-20200207162558^encntr^.txt - should match using encntr
• 20200207050000-20200207162558FinalencntrUploaded.txt - should match using encntr

The point of using this regex is to remove the inner if statement from my code. I am iterating over enum values and checking if the enum value is present in the incoming filename.

Right now the code uses txtFilename.Contains(possibleIdentifierLower, StringComparison.OrdinalIgnoreCase)) to see if the incoming filename contains one of enum values. But in the case of enum encntr, the Contains method returns true for encntr, encntrprov, and the encntrlocation filename. So I have to do an additional check to figure out which one it is. I want to leverage the regex to match only to encntr, encntrprov, or encntrlocation by supplying those values in the regex. Thus encntr couldn't not match to encntrprov or encntrlocation using the regex.

Here's the code snippet I'm trying to update.

public static FilenameIdentifierEnum IdentifyFile(string txtFilename)
{
    FilenameIdentifierEnum identifier = FilenameIdentifierEnum.unassigned;

    foreach (FilenameIdentifierEnum possibleIdentifier in Enum.GetValues(typeof(FilenameIdentifierEnum)))
    {
        // I would like this Regex.Match to eliminate the need to have the inner if statements 
        //if(Regex.IsMatch(txtFilename, $"(?i){possibleIdentifier.ToString()}(?-i)", RegexOptions.IgnoreCase))
        if (txtFilename.Contains(possibleIdentifierLower, StringComparison.OrdinalIgnoreCase))
        {
            identifier = possibleIdentifier;

            if (identifier == FilenameIdentifierEnum.encntr)
                identifier = EncntrCaseChecking(txtFilename, identifier);
            if (identifier == FilenameIdentifierEnum.appt)
                identifier = ApptCaseChecking(txtFilename, identifier);

            break;
        }
    }

    if (identifier == FilenameIdentifierEnum.unassigned)
    {
        throw new UnknownFileException($"Unknown identifier in filename or no file identifier in filename found. Text Filename: {txtFilename}");
    }

    return identifier;
}

private static FilenameIdentifierEnum EncntrCaseChecking(string txtFilename, FilenameIdentifierEnum possibleIdentifier)
{
    possibleIdentifier = (txtFilename.Contains(FilenameIdentifierEnum.encntrloc.ToString(), StringComparison.OrdinalIgnoreCase)
        ? FilenameIdentifierEnum.encntrloc
        : possibleIdentifier);

    possibleIdentifier = (txtFilename.Contains(FilenameIdentifierEnum.encntrprov.ToString(), StringComparison.OrdinalIgnoreCase)
        ? FilenameIdentifierEnum.encntrprov
        : possibleIdentifier);

    return possibleIdentifier;
}

private static FilenameIdentifierEnum ApptCaseChecking(string txtFilenameLower, FilenameIdentifierEnum possibleIdentifier)
{
    return (txtFilenameLower.Contains(FilenameIdentifierEnum.apptpart.ToString(), StringComparison.OrdinalIgnoreCase)
         ? FilenameIdentifierEnum.apptpart
         : possibleIdentifier);
}

public enum FilenameIdentifierEnum
{
    unassigned,
    encntr,
    encntrprov,
    encntrloc,
    persondemo,
    personbenefitcoverage,
    personprov,
    medication,
    immunization,
    allergy,
    diagnosis,
    problem,
    labresults,
    socialhistory,
    vitals,
    procedures,
    appt,
    apptpart,
    appointments,
    appointmentparticipant,
    encounterlocation,
    result
}

Thank you for your help.

Answer 1

Use this regular expression:

(encntr\..*?)

Matches with substring encntr. only.

Note that ^ is not a (not) operator. ^ is for matching from beginning of a string.