I want to filter out several lines before and after a matching line in a file.
This will remove the line that I don't want:
$ grep -v "line that i don't want"
And this will print the 2 lines before and after the line I don't want:
$ grep -C 2 "line that i don't want"
But when I combine them it does not filter out the 2 lines before and after the line I don't want:
# does not remove 2 lines before and after the line I don't want:
$ grep -v -C 2 "line that i don't want"
How do I filter out not just the line I don't want, but also the lines before and after it? I'm guessing sed would be better for this...
Edit: I know this could be done in a few lines of awk/Perl/Python/Ruby/etc, but I want to know if there is a succinct one-liner I could run from the command line.
6 Answers
If the lines are all unique you could grep the lines you want to remove into a file, and then use that file to remove the lines from the original, e.g.
grep -C 2 "line I don't want" < A.txt > B.txt
grep -f B.txt A.txt
Give this a try:
sed 'h;:b;$b;N;N;/PATTERN/{N;d};$b;P;D' inputfile
You can vary the number of N commands before the pattern to affect the number of lines to delete.
You could programmatically build a string containing the number of N commands:
C=2 # corresponds to grep -C
N=N
for ((i = 0; i < C - 1; i++)); do N=$N";N"; done
sed "h;:b;\$b;$N;/PATTERN/{N;d};\$b;P;D" inputfile
awk 'BEGIN{n=2}{a[++i]=$0}
/dont/{
for(j=1;j<=i-(n+1);j++)print a[j];
for(o=1;o<=n;o++)getline;
delete a}
END{for(i in a)print a[i]} ' file
I solved it with two sequential grep, actually. It seems way more straightforward to me.
grep -C "match" yourfile | grep -v -f - yourfile
I think @fxm27 has an excellent, bash-y answer.
I would add that you could solve this another way by using egrep if you knew in advance the patterns of the subsequent lines.
command | egrep -v "words|from|lines|you|dont|want"
That will do an "inclusive OR", meaning that a line that matches any of those will be excluded.
2019 Solution
This is a simple solution, found elsewhere:
grep --invert-match "test*"
Selects all not matching "test*". Super useful and easy to remember!
(Edit)
This doesn't completely answer the original question and returns the entire set of lines not matching.
