SED and regular expressions

We have already learned REGEX. Let’s learn the use of SED + REGEX by using a couple of practical exmaples:

Example 1: match patterns and REGEX (\!.*)

$ sed '/\!/s/\!.*//g' datafile

In this example, if the line matches with the pattern “!“, then it replaces all the characters from “!” with an empty char.

Example 2: use REGEX to delete the last x characters

$ sed 's/...$//' datafile

This sed example deletes last 3 characters from each line.

Example 3: use REGEX to eliminate comments (#)

$ sed -e 's/#.*//'  datafile

This sed example deletes last 3 characters from each line.

Example 4: use REGEX and eliminate Comments (#) as well as the empty lines

$ sed -e 's/#.*//;/^$/d'   datafile