How to delete from a text file, all lines that contain a specific string?

Question

How would I use sed to delete all lines in a text file that contain a specific string?

Answer 1

You can use sed to replace lines in place in a file. However, it seems to be much slower than using grep for the inverse into a second file and then moving the second file over the original.

e.g.

sed -i '/pattern/d' filename      

or

grep -v "pattern" filename > filename2; mv filename2 filename

The first command takes 3 times longer on my machine anyway.

Answer 2

cat filename | grep -v "pattern" > filename.1
mv filename.1 filename

Answer 3

perl -i    -nle'/regexp/||print' file1 file2 file3
perl -i.bk -nle'/regexp/||print' file1 file2 file3

The first command edits the file(s) inplace (-i).

The second command does the same thing but keeps a copy or backup of the original file(s) by adding .bk to the file names (.bk can be changed to anything).

Answer 4

You may consider using ex (which is a standard Unix command-based editor):

ex +g/match/d -cwq file

where:

• + executes given Ex command (man ex), same as -c which executes wq (write and quit)
• g/match/d - Ex command to delete lines with given match, see: Power of g

The above example is a POSIX-compliant method for in-place editing a file as per this post at Unix.SE and POSIX specifications for ex.

---

The difference with sed is that:

sed is a Stream EDitor, not a file editor.^BashFAQ

Unless you enjoy unportable code, I/O overhead and some other bad side effects. So basically some parameters (such as in-place/-i) are non-standard FreeBSD extensions and may not be available on other operating systems.

Answer 5

You can also delete a range of lines in a file. For example to delete stored procedures in a SQL file.

sed '/CREATE PROCEDURE.*/,/END ;/d' sqllines.sql

This will remove all lines between CREATE PROCEDURE and END ;.

I have cleaned up many sql files withe this sed command.

Answer 6

to show the treated text in console

cat filename | sed '/text to remove/d' 

to save treated text into a file

cat filename | sed '/text to remove/d' > newfile

to append treated text info an existing file

cat filename | sed '/text to remove/d' >> newfile

to treat already treated text, in this case remove more lines of what has been removed

cat filename | sed '/text to remove/d' | sed '/remove this too/d' | more

the | more will show text in chunks of one page at a time.