=====Regular Expressions=====

They are a pattern matching tool

THey are used by tools like **grep awk sed etc**

You can question the output to see if pattern was found using **$?**

====grep===

stands for global regular expression print

it will highlight the pattern if its found 

command looks like 
<code>
greo pattern  file  </code>
exit codes are using **$?**

^  0  | pattern was found  |
^  1  | pattenr not found  |
^  2  | file not found  |

grep options 
^  -n  | shows you line where pattern was found | grep -n root /etc/passwd |
^  -c  | number of lines that had the pattern  | grep -c root /etc/passwd |
^  <nowiki>^</nowiki>  | look at beginning of line only |<nowiki>grep ^pattern /etc/passwd </nowiki>|
^  $  | look at end of line | grep bash$ /etc/passwd |
^  -E  | match to more than one regular expresion |<code>grep -E 'student|devops|lolly' /etc/passwd </code>|
^  <nowiki>^[^#]</nowiki>  | give every line that does **not** begin with a **#** | <nowiki> grep ^[^#] /etc/passwd </nowiki>|


THere are loads more options