Re: [PATCH] md5sum: add an option to change directory

[Kaz Kylheku (Coreutils)]

On 2020-05-20 14:15, Bertrand Jacquin wrote:
> In the fashion of make and git, add the ability for all sum tools to
> change directory before reading a file.
>
>   $ sha256sum /etc/fstab
>   b5d6c0e5e6bc419b134478ad7b3e7c8cc628049876a7772cea469e81e4b0e0e5  
> /etc/fstab

Make requires this option because it reads a Makefile, and those often
contain relative references which assume that the Makefile's directory
is current.

The inputs to md5sum don't don't contain path references that break.

In other regards, every tool that does anything with files could
have a -C option:

Copying files:

    cp -C /etc fstab fstab.bak

Executing a script:

    sh -C /etc rc.local

Editing:

    vi -C /etc fstab

Where does it end?

>   $ sha256sum -C /etc fstab
>   b5d6c0e5e6bc419b134478ad7b3e7c8cc628049876a7772cea469e81e4b0e0e5  
> fstab

The net effect is that just the output has changed to omit the path 
name.

Maybe this wants to be a --strip or -p option like with diff or patch,
or --basename-only to strip a variable number of components, leaving 
only
the last.

If I want to print a simplified name, I don't want to do this:

   md5_short()
   {
      local dir=$(dirname "$1")
      local base=$(basename "$1")
      md5sum -C "$dir" "$basename"
   }

   md5short /path/to/whatever

I just want this:

   md5sum --basename /path/to/whatever

The -C functionality can easily be done with subshells, or with a 
chdir()
after fork(), before exec():

In a script, instead of "make -C dir", you can always do (cd dir; exec 
make).

In C, make yourself a spawning function that has the dir-changing 
functionality
built in:

   spawn_program(path_to_executable, /* or let PATH be searched */
                 change_to_this_directory,
                 use_these_args,
                 these_env_vars);