GNU bug report logs - #43282
tail -c +N / --bytes +N manpage wrong (off by 1)

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From: "Martin Taibr" <Taibr@HIDDEN>
To: <bug-coreutils@HIDDEN>
Subject: tail -c +N / --bytes +N manpage wrong (off by 1)
Date: Tue, 08 Sep 2020 17:50:50 +0200 (CEST)
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Currently the manpage says:





-c, --bytes=3D[+]NUM

=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 output the last NUM bytes; or use -c +NUM to output starting 
with byte NUM of each file




Most (all?) hex editors number bytes from 0 so it's natural to assume tail=
 -
c +0 will print the entire file, tail -c +1 will cut off the first byte an=
d 
so on. That's not the case, tail seems to "index" bytes from 1, not 0, so =
+0
and +1 both print the entire file.




I'd suggest

1) the manpage should mention counting starts from 1 (so you need to add 1=
 
when copy pasting offsets from most other programs)


2) +0 should print a warning since its usage indicates the user likely 
thinks tail counts from 0

3) -n / --lines docs should be changed to match (though counting lines fro=
m 
1 is more common)

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<html><body><div>Currently the manpage says:<br></div><div><br></div><div>=
-c, --bytes=3D[+]NUM</div><div>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&=
nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; output the last NUM bytes; or use -c +=
NUM to output starting with byte NUM of each file</div><div><br></div><div=
>Most (all?) hex editors number bytes from 0 so it's natural to assume tai=
l -c +0 will print the entire file, tail -c +1 will cut off the first byte=
 and so on. That's not the case, tail seems to "index" bytes from 1, not 0=
, so +0 and +1 both print the entire file.</div><div><br></div><div>I'd su=
ggest</div><div>1) the manpage should mention counting starts from 1 (so y=
ou need to add 1 when copy pasting offsets from most other programs)<br></=
div><div>2) +0 should print a warning since its usage indicates the user l=
ikely thinks tail counts from 0</div><div>3) -n / --lines docs should be c=
hanged to match (though counting lines from 1 is more common)<br></div></b=
ody></html>
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