grep for string not preceded by another string

Question

Is it possible, using grep, to search for instances of John Smith but exclude instances of Mr John Smith?

Answer 1

This could be solved using a regular expression with negative lookbehind (which is experimentally supported in grep as pointed out by the comment from arrange):

$ grep -P '(?<!Mr )John Smith' file

Since the support is just experimental, you might want to use perl instead:

$ perl -nle 'print if /(?<!Mr )John Smith/' file

Answer 2

You can execute

command | grep 'John Smith' | grep -v 'Mr John Smith'

Answer 3

To use regular expressions, use ^ and $

grep "^John Smith$"

^ is match from the beginning $ is match from end.

The syntax will vary depending on what you are searching for in what file.

You can use regular expressions with sed, grep, awk ....

Example

bodhi@Ubuntu:~ cat file
Mr John Smith
John Smith
John
Smith

bodhi@Ubuntu:~ grep "^John Smith$" file
John Smith