Regex and VB.net pattern matching

Question

I am writing a VB.net program to detect a words. Here is my sample text file:

EXTERNAL 16EVP_PK   -- FL(4) TDC PERMIT CONTRL TO MESTO CONTRL  
                    -- FL(5) $HY04B09.BOXTSTAT (= RUN = ON)   
EXTERNAL 16EVPUPK   -- FL(33) REQUEST FROM METSO FOR CONTRL   
EXTERNAL 16SA0541                                 -- SP VALUES TRANSFERS  
EXTERNAL 16FC0730, 16FC0815, 16FC0830   -- Hiway 4 Tags   
EXTERNAL 16FC1525                       -- Hiway 4 Tags

I want to detect everything after EXTERNAL and before -- (EXTERNAL can be external or ExTernal or any combination) . The first match should read "16EVP_PK" second match 16EVPUPK third match 16SA0541 fourth match "16FC0730, 16FC0815, 16FC0830" and so on

Here is the code that I have written:

Private Sub CheckCLFile()
path="D:\16METEVP.CL"
'Read CL file
Dim value As String = System.IO.File.ReadAllText(path)
Dim Pattern As String = "(?m)(?<=\bExternal).*$"
Debug.WriteLine(value)
Debug.WriteLine(Regex.Matches(value, Pattern).Count())
For Each m As Match In Regex.Matches(value, Pattern)
Console.WriteLine("'{0}' found at index {1}.",
                          m.Value, m.Index)
Next
End Sub

Thanks in advance.

Gurmanjot Singh · Accepted Answer · 2017-11-23 03:09:11Z

1

Try this Regex:

(?<=EXTERNAL)\s*.*?(?=\s*--)

With this you will get extra leading spaces before each match. I guess, you can easily trim that before using the matches.

Click for Demo

Explanation:

(?<=EXTERNAL) - Positive lookbehind to find the position immediately preceded by EXTERNAL. Switch the Ignore Case flag ON.
\s* - matches 0+ occurrences of white-spaces, as many as possible
.*? - This is your actual match. It matches 0+ occurrences of any character but a new-line character, as few as possible
(?=\s*--) - Positive lookahead to validate that the match must be followed by 0+ spaces followed by --

edited Nov 23, 2017 at 3:09

answered Nov 23, 2017 at 3:00

Gurmanjot Singh

10.4k2 gold badges22 silver badges46 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

TanuAD Over a year ago

Gurman - very close, but where 3 tags (16FC0730, 16FC0815, 16FC0830 ) needs to be selected, I see only one (16FC0730). I need to select everything after External but before --. Thanks.

Gurmanjot Singh Over a year ago

Hi...I hadn't read that properly..I have now updated the solution

TanuAD Over a year ago

Very nice explanation. Learned something new about Regex. Thanks Gurman.

PJProudhon Over a year ago

Using .NET, thus no need for the lookbehind to be fixed length, no need to trim leading spaces if \s* goes into it.

Gurmanjot Singh Over a year ago

@PJProudhon Thanks for that information. I didn't know about that. Here is the updated solution (?<=EXTERNAL\s+).*?(?=\s*--)

Collectives™ on Stack Overflow

Regex and VB.net pattern matching

1 Answer 1

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related