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

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

This is how I did it:

开发者_开发百科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?

sed '/pattern/!d' file.txt

But you're reinventing grep here.

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.

This might work for you:

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

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

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

grep matching_pattern file

This should give you the desired result.