fix: add Perl compatible grep regexp solution

The solution to the first character class exercise was wrong due to not using the appropriate grep flag (-E instead of -P).

8_text_manipulation.Rmd

@@ -44,7 +44,7 @@ The program `grep string` allows you to search for *string* through a file or st
 gzip -dc hg38.ncbiRefSeq.gtf.gz | grep "chr2" | head
 ```
 
-What is the last annotation on the chromosome 1 (to write a tabulation character you can type `\t`) ?
+What is the last annotation on the chromosome 1 ?
 
 You can count things in text file with the command `wc` read the `wc` **man**ual to see how you can count lines in a file.
 
@@ -54,7 +54,7 @@ How many transcripts does the gene *CCR7* have ?
 
 ## Regular expression
 
-When you do a loot text search, you will encounter regular expressions (regexp), which allow you to perform fuzzy search. To run `grep` in regexp mode you can use the switch. `-E`
+When you do a loot text search, you will encounter regular expressions (regexp), which allow you to perform fuzzy search. To run `grep` in regexp mode you can use the switchs `-E` or `-P` for Perl regexp.
 
 The most basic form fo regexp si the exact match:
 
@@ -90,7 +90,11 @@ Search for two digits followed by an uppercase letter and one digit.
 <details><summary>Solution</summary>
 <p>
 ```sh
-gzip -dc hg38.ncbiRefSeq.gtf.gz | head | perl -E "\d\d[A-Z]\d"
+gzip -dc hg38.ncbiRefSeq.gtf.gz | grep -E "[0-9][0-9][A-Z][0-9]"
+```
+We need to use the flag `-P` to use the character class `\d`:
+```sh
+gzip -dc hg38.ncbiRefSeq.gtf.gz | grep -P "\d\d[A-Z]\d"
 ```
 </p>
 </details>