Remove all lines except matching pattern line best practice (sed)

Question

I want to remove all lines except the line(s) containing matching pattern.

This is how I did it:

sed -n 's/matchingpattern/matchingpattern/p' file.txt

But I'm just curious because I rename matching pattern to the matching pattern itself. Looks like a waste here.

Is there a better way to do this?

score 56 · Accepted Answer · answered May 07 '11 at 17:11

56

sed '/pattern/!d' file.txt

But you're reinventing grep here.

answered May 07 '11 at 17:11

geekosaur

14

Yup. But sed has this nifty --in-place flag that grep does not have. sed -i '/pattern/!d' filename is much easier than grep 'pattern' filename > filename.tmp && mv filename.tmp filename – Geeklab Apr 24 '15 at 08:19
Warning: I supplied the --quiet flag to avoid any results to be printed to the terminal, not realizing -i already achieves that in itself. This meant that all lines were deleted, even those matching the pattern. – EriF89 Jul 07 '17 at 10:20

score 4 · Answer 2 · answered Jan 29 '14 at 00:57

grep is certainly better...because it's much faster.

e.g. using grep to extract all genome sequence data for chromosome 6 in a data set I'm working with:

$ time grep chr6 seq_file.in > temp.out

real    0m11.902s
user    0m9.564s
sys 0m1.912s

compared to sed:

$ time sed '/chr6/!d' seq_file.in > temp.out

real    0m21.217s
user    0m18.920s
sys 0m1.860s

I repeated it 3X and ~same values each time.

score 2 · Answer 3 · answered Jul 25 '12 at 04:34

2

Instead of using sed, which is complicated, use grep.

grep matching_pattern file

This should give you the desired result.

answered Jul 25 '12 at 04:34

reFORtEM

+1 for the 'right tool.' but sed can modify a file in place. – Aryeh Leib Taurog Aug 14 '14 at 19:37

score 2 · Answer 4 · answered Jan 22 '12 at 10:26

2

This might work for you:

sed -n '/matchingpattern/p' file.txt

/.../ is an address which may have actions attached in this case p.

answered Jan 22 '12 at 10:26

potong

4 Answers4