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I am trying to parse the date out of this file name with regex.

LBX845656_PayOnline_0528-20191429.txt.052819220054.bak

The problem I am encountering is that I need the regex to match the entire filename, while capturing a group with the Date in it.

I have written this regex to capture the Date in capture group 1:

([0-9]{0,8}(?=\.txt))

Using a regex tester online, this seems to capture the correct string from the filename I am looking for, but I cant figure out how to also get the regex to match the whole string.

Here is what I want to return

FULL MATCH: LBX845656_PayOnline_0528-**20191429**.txt.052819220054.bak CAPTURE GROUP 1: 20191429

Thanks in advance for any advice.

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  • \w+_\w+_\d+-([0-9]{0,8}(?=\.txt)).txt.\d+.bak Would match what you currently have at least.. Not sure what other variations you can have for that string though Commented Jun 18, 2019 at 18:34
  • What do you mean by "match the whole string"? Commented Jun 18, 2019 at 18:35
  • Is that OK for you? Commented Jun 18, 2019 at 18:36
  • You do not need to match the whole string if you want to get the string matched with [0-9]{0,8}(?=\.txt), you just need matcher.find() Commented Jun 18, 2019 at 18:44
  • @WiktorStribiżew The OP said they needed to match both the entire string and if it matches, grab the date portion. That's a requirement for the OP, not for for the regex engine. Imo you closed down the discussion too early, And that specific topic was not covered in your cited question. Commented Jun 18, 2019 at 19:02

1 Answer 1

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I think this is a simpler regex that will solve your problem, assuming the date is always 8 digits.

Option 1

If you can assume that the date is the only 8 digit string in the filename

^.*[^\d](\d{8})[^\d].*$

Option 2

If you want to assume that it is preceded by a "-" and has a "." after

^.*-(\d{8})\..*$

Options 3

If you want to assume it is followed by .txt

^.*(\d{8})\.txt.*$

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2 Comments

As an aside, 20191429 does not look like the date, since 14 and 29 are both invalid for month. What it looks like to me is 0528-20191429 is the date plus (possibly) the time (May 28, 2019 at 2:29pm)
Thanks for your answer Robert. And ugh, yes noticed that after posting. Date format int the file is "MMDD-YYYYMMSS". But I can definitely work with what you have provided me, I was thinking about the regex in the wrong way. Thanks again.

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