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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?

2020/05/13
1
1832
5/13/2020 12:03:41 AM

Accepted Answer

To remove the line and print the output to standard out:

sed '/pattern to match/d' ./infile

To directly modify the file – does not work with BSD sed:

sed -i '/pattern to match/d' ./infile

Same, but for BSD sed (Mac OS X and FreeBSD) – does not work with GNU sed:

sed -i '' '/pattern to match/d' ./infile

To directly modify the file (and create a backup) – works with BSD and GNU sed:

sed -i.bak '/pattern to match/d' ./infile
2019/06/27
2831
6/27/2019 9:57:09 AM

There are many other ways to delete lines with specific string besides sed:

AWK

awk '!/pattern/' file > temp && mv temp file

Ruby (1.9+)

ruby -i.bak -ne 'print if not /test/' file

Perl

perl -ni.bak -e "print unless /pattern/" file

Shell (bash 3.2 and later)

while read -r line
do
  [[ ! $line =~ pattern ]] && echo "$line"
done <file > o
mv o file

GNU grep

grep -v "pattern" file > temp && mv temp file

And of course sed (printing the inverse is faster than actual deletion):

sed -n '/pattern/!p' file
2018/09/15

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.

2015/08/19

The easy way to do it, with GNU sed:

sed --in-place '/some string here/d' yourfile
2017/12/11

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.

2018/09/15

I was struggling with this on Mac. Plus, I needed to do it using variable replacement.

So I used:

sed -i '' "/$pattern/d" $file

where $file is the file where deletion is needed and $pattern is the pattern to be matched for deletion.

I picked the '' from this comment.

The thing to note here is use of double quotes in "/$pattern/d". Variable won't work when we use single quotes.

2018/09/15

Source: https://stackoverflow.com/questions/5410757
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