Question

What would be the regular expression to match a string with two underscores breaking up a 3 series of characters. This can also be a SQL ‘like’ statement if that is possible.

Match:

b_06/18/2012_06:02:34 PM 
y1289423_06/14/2011_03:06:35 AM 
23479693_11/01/2011_06:12:55 PM 

Not Match:

CCC Valuation_b_06/28/2012_05:57:20 PM 
CCC Valuation_CCC Valuation_b_06/28/2012_05:57:20 PM 
doc1_2.pdf 
testdoc.txt

Answer 1

If all of the data is consistent with your examples, then this should work:

EDIT: Updated to match the whole line. This will preclude any substring matches in the invalid list. However, it assumes that OP does not want to match any substrings.

^[a-z0-9]+_[0-9\/]+_[A-Z0-9:\s]+$

For example, in python:

>>> import re
>>> s = 'b_06/18/2012_06:02:34 PM'
>>> pattern = '^[a-z0-9]+_[0-9\/]+_[A-Z0-9:\s]+$'
>>> m = re.match(pattern, s)
>>> m.group(0)
'b_06/18/2012_06:02:34 PM'            # <======== matches from valid list

>>> s = 'CCC Valuation_CCC Valuation_b_06/28/2012_05:57:20 PM'
>>> m = re.match(pattern, s)
>>> m.group(0)
Traceback (most recent call last):    # <======= does NOT match from invalid list
  File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'group'