I have these strings in a folder. Assume there are other similar files in this folder.

```
 [3] "/farm/chickens_industrial_meat_location_df.csv"   
 [4] "farm/goats_grassland_meat_location_df.csv" 

```

I am trying to extract the files with string `location_df` while excluding the files with the string `chickens` & `location_df`.

I thought I could do this by typing: `list.files(pattern = "location_df(?<!(chickens))"`

My understanding is that using a negative lookaround would remove strings that have `chickens`. What am I not understanding about regex here and what is the solution to my problem.