What is Regular Expression?

It is used for Pattern Matching

How to write Regular expressions

• search for the occurrence of complete text

<text>

## sample ###

Microsoft & Linux are the popluar operating systems

To search operating

reg => operating

• Searching for beginning of the line

Microsoft is commercial OS.
Most popular Desktop Os is from Microsoft
Linux is opensource os.
Most popular Server Os is from Linux

Regex for lines which begin with Linux
^Linux

• Searching for the end of the line

Microsoft is commercial OS.
Most popular Desktop Os is from Microsoft
Linux is opensource os.
Most popular Server Os is from Linux

Regex for lines ending with Linux
Linux$

• Searching for any character with word combinations

msoft
softm
nsofty
ysoftn

Regex for the lines with 1 character before soft
^.soft

Regex for the lines with 1 character before soft and ends there
^.soft$

• Repetition using {}
• Grouping using ()

Exercise

• Create a file with following content

linux is an os. Linux is opensource. 
you can choose between different distributions of Linux such debian, redhat.
Linux is inspired from Unix.
Linux can be alternative to unix and windows
linux is also considerd as nix platform where linux, unix are part of it.
Posix is a popular format.

• search for all the occurrences of Linux irrespective of case
• Display the count of occurrences of Linux & Linux and both the cases
• Show the line number where windows is present
• Display all the lines which do not have windows
• Write a regular expression to search for nix or unix or Posix