RegEx for Date

I have a large file with, roughly, 20K lines.  The lines I'm interested in start with DTP*348*D8* and then the date in yyyymmdd format.  Example: DTP*348*D8*20150601

What pattern would I use to find all of those lines where the date is prior to 20140601?

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NVITEnd-user supportCommented:
If you are ok with using the Windows CMD prompt and a .bat file, make a .bat file of this code.
Change the following variables to your needs:
- CompStr
- SrcFN
- IntFN
- ResultsFN

Note: ResultsFN is appended to at each run of the .bat. If you want to run it more than once, rename ResultsFN before running it.

set CompStr=20140601
set SrcFN=GiantFile.txt
set IntFN=x2.txt
set ResultsFN=xResults.txt
findstr /n /r DTP\*348\*D8\* "%SrcFN%" >"%IntFN%"
for /f "tokens=1-5* delims=*" %%a in (%IntFN%) do (
  if %%d lss %CompStr% echo %%a*%%b*%%c*%%d %%e>>"%ResultsFN%"
del /q "%IntFN%"

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yukonjayAuthor Commented:
I would prefer a regex as I will be using it as part of a C# application to modify particular lines in a file.  Is there a way I can incorporate your suggestion into that solution?
Shahan AyyubSenior Software EngineerCommented:
Since you want to first find out the string and then process the date inside string. You have to do it in two steps as I see:

First find the string using regex with this pattern:

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Then using the first group of this match parse it to a date time object, probably using `DateTime.ParseExact` function. Then you have datetime object so you can compare this date with your required date and keep relevant records in `List<string>`.

If you need more on this please let me know.

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Regular Expressions

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