Re: Enhancement Request for sha256sum - output only the SHA-256 hash alone

[Erik Auerswald]

On Fri, Jul 17, 2020 at 11:35:02PM -0600, Bob Proulx wrote:
> Pádraig Brady wrote:
> > jens wrote:
> > > It would make shell scripts that use sha256sum much simpler. Currently it
> > > is necessary to split the output of sha256sum to obtain the hash, which
> > > usually requires an additional command / Unix process.
> > 
> >   sum=$(sha256sum file | cut -d ' ' -f 1)
> > 
> > Yes that's an extra process, but you can easily
> > enough avoid that on any POSIX shell using:
> > 
> >   sum=$(sha256sum file) && sum=${sum%% *}
> 
> I'll suggest always using stdin instead ("sha256sum < file") as that
> avoids any possible quoting of things to get in the way.  In the case
> where the filename contains special characters.

To illustrate this with an example:

    $ touch foo\\bar
    $ sha256sum foo\\bar
    \e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855  foo\\bar
    $ sha256sum < foo\\bar
    e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855  -
    $ sha256sum foo\\bar | cut -d' ' -f1 | sed 's/^\\//'
    e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
    $ sha256sum < foo\\bar | cut -d' ' -f1
    e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

The Asterisk ('*') denoting "binary mode" is part of the second whitespace
separated field and can thus be ignored here.

HTH,
Erik
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