I need to remove odd lines in a text file to make a down-sampling. I've found this command,
awk 'NR%2==0' file
but it only prints the odd lines in the terminal. How to really remove them?
I don't really care for even or odd, I want them removed from the file or printed in another file. This only prints them in the terminal.
The %
is a modulus operator and NR
is the current line number, so NR%2==0
is true only for even lines and will invoke the default rule for them ({ print $0 }
). Thus to save only the even lines, redirect the output from awk
to a new file:
awk 'NR%2==0' infile > outfile
You can accomplish the same thing with sed
. devnulls answer shows how to do it with GNU sed
.
Below are alternatives for versions of sed
that do not have the ~
operator:
keep odd lines
sed 'n; d' infile > outfile
keep even lines
sed '1d; n; d' infile > outfile