Re: [hackers] [sbase] [PATCH 11/11] tail: Process bytes with -c option, and add -m option for runes

From: Laslo Hunhold <>
Date: Tue, 27 Dec 2016 14:55:42 +0100

On Tue, 6 Dec 2016 02:17:03 -0800
Michael Forney <> wrote:

Hey Michael,

> POSIX says that -c specifies a number of bytes, not characters. This
> flag is commonly used by scripts that operate on binary files to do
> things like extract a header. Treating the offsets as character
> offsets will break things in mysterious ways.
> Instead, add a -m option (chosen to match `wc -m`, which also operates
> on characters) to handle character offsets.
> ---
> I'm tempted to just delete the character functionality instead of
> introducing a new non-standard option. I can see the use of tail with
> codepoints, but we definitely need to make -c work on bytes so that we
> don't break scripts.
> I'm also open to changing the option flag to something else. I just
> chose -m because that's what wc uses for characters.

well-spotted! Still, it's _very_ counterintuitive to call the flag
"-c". Instead of adding a non-portable m-flag, it would even sound
better to me to add a b-flag for byte-offsets.

It all depends on how many scripts rely on this behaviour. Can you give
an example? I thought cut(1) was the tool of choice for extracting
headers and such things.



Laslo Hunhold <>
Received on Tue Dec 27 2016 - 14:55:42 CET

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