remove multiple lines from text file using grep

Question

I would like to remove unwanted lines from my text file had certain words. i have use grep -v like this

grep -v 'error|fault|unkownn' input.txt > out.txt

it's working with one word but not on multiple words. did i miss anything?

Answer 1

| is only treated as a a regex character when grep is working in extended regex mode. So you need to do one of the following:

# Escape the | so that it's treated as a regex control character
grep -v 'error\|fault\|unkownn' input.txt > out.txt

# -E enables extended regex mode
grep -vE 'error|fault|unkownn' input.txt > out.txt

# egrep = grep -E
egrep -v 'error|fault|unkownn' input.txt > out.txt