Update file UNIX_HPC_exercise_instructions.md

exercises/UNIX_HPC_exercise_instructions.md

@@ -269,7 +269,7 @@
 
 5. Extracting parts of a character string:
    ```sh
-   grep "variant" all_ompA.fasta | cut -d '-' -f 3       # or use the headers file
+   grep "variant" all_ompA.fasta | cut -d '_' -f 3       # or use the headers file
    ```
 6. Concatenating input and files
    ```sh