Re: md5sum outputs '-' when using stdin

[Stephane Chazelas]

2019-08-25 21:03:33 +0100, Stephane Chazelas:
[...]
> FWIW, the ast-open implementation of "wc" doesn't output that
> "-" and doesn't treat "-" as meaning stdin. If you want to
> "md5sum -c" stdin there, you need to use "/dev/stdin" instead of
> "-".
[...]

Sorry, I meant "the ast-open implementation of md5sum", not
"wc". That's also the md5sum builtin of the ksh93 shell when
built as part of ast-open (not enabled by default unless
/opt/ast/bin is ahead of /bin in $PATH).

$ printf '%s\n' "${.sh.version}"
Version ABIJM 93v- 2014-12-24
$ builtin md5sum
$ echo test | md5sum
d8e8fca2dc0f896fd7cb4cb0031ba249

I was also wrong about using /dev/stdin to be able to "check"
checksums for stdin:

$ echo test | md5sum /dev/stdin
d8e8fca2dc0f896fd7cb4cb0031ba249
$ echo test | md5sum /dev/fd/0
d8e8fca2dc0f896fd7cb4cb0031ba249

ast-open's md5sum treats /dev/fd/0 and /dev/stdin the same way
GNU md5sum treats "-". It doesn't open the /dev/fd/0 and
/dev/stdin files.

You'd need to use something like:

$ echo test | md5sum /dev/fd//0
d8e8fca2dc0f896fd7cb4cb0031ba249 */dev/fd//0

(in which case ast-open md5sum *does* open /dev/fd/0)

$ echo test | md5sum -c <(echo test | md5sum /dev/fd//0) && echo OK
OK
$ echo toast | md5sum -c <(echo test | md5sum /dev/fd//0) && echo OK
md5sum: /dev/fd//0: checksum changed

-- 
Stephane

Re: md5sum outputs '-' when using stdin

[Bernhard Voelker]

On 8/26/19 10:44 AM, Erik Auerswald wrote:

On Sun, Aug 25, 2019 at 09:03:33PM +0100, Stephane Chazelas wrote:

[...]
Maybe --quiet could be used to skip outputting file names.


I don't think overloading --quiet this way is helpful.

Changing *sum's output format should use a new option IMHO (if one wants
to add this functionality and the maintainers do not object).


This has already been discussed:

  https://www.gnu.org/software/coreutils/rejected_requests.html#checksum
  "*sum --no-filename to only output the checksum.
   Postprocessing the output was deemed sufficient"

... pointing at:

  https://lists.gnu.org/archive/html/coreutils/2014-04/msg00025.html

Have a nice day,
Berny

Re: md5sum outputs '-' when using stdin

[Erik Auerswald]

Hi,

On Sun, Aug 25, 2019 at 09:03:33PM +0100, Stephane Chazelas wrote:
> [...]
> Maybe --quiet could be used to skip outputting file names.

I don't think overloading --quiet this way is helpful.

Changing *sum's output format should use a new option IMHO (if one wants
to add this functionality and the maintainers do not object).

Thanks,
Erik
-- 
Be water, my friend.
-- Bruce Lee

Re: md5sum outputs '-' when using stdin

[Stephane Chazelas]

2019-08-23 10:41:01 +0100, coreut...@fastmail.com:
[...]
> $ echo 'hello world' | md5sum
> 6f5902ac237024bdd0c176cb93063dc4  -
> 
> What's use is the '-'?
> 
> Obviously it indicates the file content it taken from the
> standard input, but is that of any actual use?
[...]

It is used by md5sum -c.

$ echo test | md5sum | tee s
d8e8fca2dc0f896fd7cb4cb0031ba249  -
$ echo test | md5sum -c s
-: OK

Having said that, it's far less common a usage pattern than doing:

sum=$(md5sum < file)

And I agree it is annoying having to strip that "-".

It's the same kind of "annoying" as the

length=$(wc -c < file)

That has blanks around the number in many wc implementations and
which GNU wc fixed.

FWIW, the ast-open implementation of "wc" doesn't output that
"-" and doesn't treat "-" as meaning stdin. If you want to
"md5sum -c" stdin there, you need to use "/dev/stdin" instead of
"-".

I'd rather GNU md5sum only output "-" when "-" is passed on the
command line.

Maybe --quiet could be used to skip outputting file names.

-- 
Stephane