Regex in C# that contains "this" but not "that

Question

I need to filter a list of files. Some of these are csv files, and of those, some of them are appended with a control tag, ".cntl".

Example: file1.csv, file1.csv.cntl

I would like to set up a regex that checks to see if a file contains "csv" and NOT "cntl". Right now I've got this.

csv(?!cntl)

This is not working. What would a proper regex be?

PS. This is all done in C#.

score 9 · Accepted Answer · answered Dec 09 '10 at 20:31

9

Your regex should check to see if a file ends with .csv

\.csv$

Remember that csv could be contained elsewhere in the file name.

answered Dec 09 '10 at 20:31

Seattle Leonard

Lot of varied answers, but this is incredibly simple. Thank you. – Nick Vaccaro Dec 09 '10 at 21:02
1

@Norla, I'd have to argue that checking `string.EndsWith()` is far more simple than using a regex in the first place. – jjnguy Dec 09 '10 at 21:31

jjnguy · Answer 2 · 2010-12-09T20:45:52.807

7

The following is the pattern you want.

@"csv(?!\.cntl)"

But, wouldn't it be easier to check:

if (string.EndsWith("cntl"))

Using a regex is unnecessarily complicated.

edited Dec 09 '10 at 20:45

answered Dec 09 '10 at 20:32

jjnguy

I don't think that `@"csv!(?\.cntl)"` is a valid regex. – eldarerathis Dec 09 '10 at 20:40
@eldare, I was having that same feeling, but I couldn't decide what I thought was wrong with it. What do you think is wrong? – jjnguy Dec 09 '10 at 20:43
@jjnguy: Negative lookahead should be `(?!)`. If you move the `!` it ought to be fine (and a quick test seems confirm that). – eldarerathis Dec 09 '10 at 20:45

score 0 · Answer 3 · answered Dec 09 '10 at 20:31

0

This should work:

csv(?!.*cntl)

answered Dec 09 '10 at 20:31

cdhowie

If you have not "." will it be possible to have a file that is not a "csv" real file. "Myfilecsv" will to go to true – eriksv88 Dec 09 '10 at 20:39
@sv88erik: Yes, but that's not the question the OP asked. – cdhowie Dec 09 '10 at 20:39
1

"Example: file1.csv, file1.csv.cntl" : as shown in this syntax :) – eriksv88 Dec 09 '10 at 20:41
*"I would like to set up a regex that checks to see if a file contains 'csv' and NOT 'cntl'."* – cdhowie Dec 09 '10 at 20:42
And I reckon that this is the fault of the OP, then eksplene and file validation of file extensions. But of course you have a point that it has two different answers if you choose to interpret it as you do – eriksv88 Dec 09 '10 at 20:53

3 Answers3