[fernape@vm-current ~]$ cat example.txt
a
b
c
d
[fernape@vm-current ~]$ echo -e "B\nc" | comm example.txt -
        B
a
b
                c
d
[fernape@vm-current ~]$ uname -a
FreeBSD vm-current 13.0-CURRENT FreeBSD 13.0-CURRENT #0 r362494: Mon Jun 22 20:26:42 CEST 2020     root@vm-current:/usr/obj/usr/src/amd64.amd64/sys/GENERIC  amd64

and exactly the same output in 12.1-RELEASE.

I suspect it might be the environment. In my case, the variables that affect the behavior of comm(1) are cleared:

$ echo $LANG $LC_ALL $LC_COLLATE $LC_CTYPE
$

This is the output from freefall

[fernape@freefall ~]$ echo -e "B\nc" | comm example.txt -
        B
a
b
                c
d
[fernape@freefall ~]$ uname -a
FreeBSD freefall.freebsd.org 13.0-CURRENT FreeBSD 13.0-CURRENT #0 r360534: Fri May  1 17:50:03 UTC 2020     sbruno@build-13.freebsd.org:/usr/obj/usr/src/sys/CLUSTER13  amd64

In D25344#572178, @fernape wrote:

This is the output from freefall

[fernape@freefall ~]$ echo -e "B\nc" | comm example.txt -
        B
a
b
                c
d
[fernape@freefall ~]$ uname -a
FreeBSD freefall.freebsd.org 13.0-CURRENT FreeBSD 13.0-CURRENT #0 r360534: Fri May  1 17:50:03 UTC 2020     sbruno@build-13.freebsd.org:/usr/obj/usr/src/sys/CLUSTER13  amd64

I have some language settings for german umlauts active, but I didn't remember which ones. So I would think that this differential is fine.

This revision is now accepted and ready to land.Jul 27 2020, 3:55 PM

Closed by commit rS363620: comm(1): Add EXAMPLES section (authored by fernape). · Explain WhyJul 27 2020, 4:51 PM

This revision was automatically updated to reflect the committed changes.

fernape added a commit: rS363620: comm(1): Add EXAMPLES section.

In D25344#572188, @gbe wrote:
In D25344#572178, @fernape wrote:
This is the output from freefall
[fernape@freefall ~]$ echo -e "B\nc" | comm example.txt -
        B
a
b
                c
d
[fernape@freefall ~]$ uname -a
FreeBSD freefall.freebsd.org 13.0-CURRENT FreeBSD 13.0-CURRENT #0 r360534: Fri May  1 17:50:03 UTC 2020     sbruno@build-13.freebsd.org:/usr/obj/usr/src/sys/CLUSTER13  amd64
I have some language settings for german umlauts active, but I didn't remember which ones. So I would think that this differential is fine.