reg exp

^ (caret)  = match expression at the start of the line, as in ^A

$ (question) = match expression at the end of the line , as in A$

\ (blash slash) = turn off the special meaning of the text, as in \^

[ ] (bracket) = match any one of the enclosed character, as in [aeiou] use hyphen for range as in [0-9]

[^] = match any one character expect those enclosed in [] , as in [^0-9  ]

. (Period) = match a single character of the any value, expect end of line. 

* (asterisk) = match zero or more of the preceding character or expression. 

\{x, y\} = match x and y occurrence  the preceding

\ { x\} = match exactly x occurrence of the preceding

\{x, \} = match x or morecl occurrence of the preceding. 

grep shravan  file {search files for line with shravan}

grep '^shra' file {'shra' at the start of the line}

grep 'shra$ ' file {'shra' at the end of the line}

grep '^shra$' file {line Containing only shra}

grep '^\^ s' file { line starting with ^s, \ escape the ^}

Grep '[Ss]hra' file { search for shra or Shra}

Grep '[Dd][Oo]g' {search for Dog, dog, DOg, dOg}

Grep '^$' file { search for blank lines}

Grep '[0-9][0-9] ' file {search for pair of numertic digital}