Sed "N" command multiline output with embedded newline expected result

Question

I'm on macOS 12.6 and have an issue with the multiline commands in sed.

From this script (taken from the manual): seq 6 | sed -n 'N;l;D' I should get this output:

1\n2$
2\n3$
3\n4$
4\n5$
5\n6$

But this is what I get:

1$
2$
2$
3$
3$
4$
4$
5$
5$
6$

I can't figure out why the newline isn't printed unambiguously (that's what the "l" command does)

Thanks in advance!

I can't reproduce _with GNU sed v4.8_, I am getting the first output. Are you sure that you are really running the command you are running? What sed version and operating system are you using? — KamilCuk, Oct 13 '22 at 16:26
@KamilCuk I'm on macOS 12.6 therefor I can't tell exactly the version (or maybe yes, but not with `sed --version` as I've just read [here](https://stackoverflow.com/questions/37639496/how-can-i-check-the-version-of-sed-in-os-x)). The date in the man page is June 10, 2020. — ranemirusG, Oct 13 '22 at 17:50
I believe macos sed is based on freebsd sed. If you look at the [manual page](https://www.freebsd.org/cgi/man.cgi?query=sed&apropos=0&sektion=0&manpath=FreeBSD+13.1-RELEASE+and+Ports&arch=default&format=html) there is no reference to newline, so I would guess it is shown as is. — potong, Oct 13 '22 at 22:57
@HatLess I ended up by doing this and adding `alias sed="gsed"` in my .zshrc — ranemirusG, Oct 14 '22 at 16:32

score 1 · Accepted Answer · answered Oct 14 '22 at 09:36

why the newline isn't printed unambiguously

Because you are using BSD sed, not GNU sed, the newline is printed "ambiguously".

https://github.com/chimera-linux/bsdsed/blob/master/process.c#L627 -> prints a $+newline on newline. (The check above when the line is longer than terminal width.)

I should get this output:

l command is not standardized. Every sed can do what it wants with it. GUN sed prints it that way, BSD sed prints it the other, you can't expect.

1 Answers1