there are similar questions here but none matches my problem exactly.
How do I remove only the first blank line from a file using sed?
Let's say I have
a b c And I want
a b c As output.
2 Answers
See the sed FAQ here:
$ sed '0,/^$/{//d}' lines a b c d Note this only removes truly empty lines, if you want to consider lines with whitespace you would use
$ sed '0,/^[[:space:]]*$/{//d}' lines instead.
- That's not standard
sedsyntax though.Stéphane Chazelas– Stéphane Chazelas2013-05-11 14:11:35 +00:00Commented May 11, 2013 at 14:11 - @Stephane The link states several non-GNU
sedalternatives, though.Adrian Frühwirth– Adrian Frühwirth2013-05-11 14:13:34 +00:00Commented May 11, 2013 at 14:13
You can use sed to read up to the first blank line, and then use cat to read the rest which would be the most efficient for big files:
{ sed -n '/./!q;p'; cat; } < the-file It only works with regular files though (not with pipes because sed reads data by blocks and can't seek back to the line after the one where q was called if the input is not seekable). As noted by @peterph, With GNU sed version 4.2.2 and above, you can add the -u flag which causes GNU sed to read its input one byte at a time (and output one line at a time) and removes the problem with pipes (though degrading performance).
answered May 11, 2013 at 14:11
Stéphane Chazelas
586k96 gold badges1.1k silver badges1.7k bronze badges
- GNU sed (at least) has the
-uoption which should reduce buffering.peterph– peterph2013-05-13 09:44:17 +00:00Commented May 13, 2013 at 9:44 - @peterph, with
-u, GNU sed will still read data by blocks (4k according tostracewithsed4.2.1, eglibc 2.13, Linux amd64) so it won't help here. I've clarified what I meant by buffering.Stéphane Chazelas– Stéphane Chazelas2013-05-13 10:56:48 +00:00Commented May 13, 2013 at 10:56 - 1GNU sed 4.2.2 does a 1B read here in
cat file | sed -u.peterph– peterph2013-05-13 11:19:51 +00:00Commented May 13, 2013 at 11:19 - @peterph, Indeed, that's a new feature added in 4.2.2 (see commit log)Stéphane Chazelas– Stéphane Chazelas2013-05-13 13:01:10 +00:00Commented May 13, 2013 at 13:01
sed?awk 'a||$0;!$0{a=1}'$0resolve to false if the line is empty or resolves to a numerical 0 (like00or0.0or0e12...). Use$0 != ""instead. Test forNFfor non-blank lines.awk 'a||NF;!NF{a=1}'