Re: Bug or not a bug? dot expansion in ob-shell

[Tim Cross <theophilusx@gmail.com>]

I think I agree with Eric here. However, perhaps I don't fully
understand all the details.

Many shell commans, especially those
which mainly perform 'side effects' like echo, return the exit code.
This value is often used in shell scripts as a type of short hand/short
circuit i.e. combined with logic operators.

Question: would it not be import to separate return value from output
value when it comes to shell scripts and noweb type expansion e.g. if I
had a block where the last command does not do any output, but does
return an exit value as the return value, might it not be important to
have that exit value for the next babel block which uses the previous
block?

Something else which may be relevant is to note that bash is not the
only shell and some commands, like echo, will behave differently
depending on the shell. For exmaple, in some shells, echo with no
arguments will just ouput a newline while on other shells, you need to
explicitly request this behaviour with -n switch.

As a general principal, I think the return value and the output value
should be considered to be distinct items and it would be a mistake to
return the output value when it appears the last command does not return
a value. Do what the shell would do - if it returns the exit code then
return that. If the last command really doesn't return anything i.e. hot
even an exit code, return nil (though I think under posix, at the very
least, the exit code is returned).

Fraga, Eric <e.fraga@ucl.ac.uk> writes:

> On Wednesday, 19 Feb 2020 at 12:38, Bastien wrote:
>> "0" is the _exit code_ of the successful echo command, not the value
>> returned by the echo command.
>
> But echo does not "return" the string as a value.  It outputs the
> string.
>
> To quote the man page for bash, "the return value of a simple command is
> its status".  Further, a function does not actually return any value
> beyond the status of the last command or a value given on a =return=
> statement.
>
>> So In Vladimir's example, both ":results value" and ":results output"
>> should return the same result, i.e. ".".
>
> I disagree.  I think the current behaviour (i.e. before your attempt to
> "correct"" this) is correct given the documentation you quoted!
>
>> Was it common to expect the exit code when executing shell code?
>
> Common?  I have no idea.  *I* did expect this.  But that's maybe because
> I do use the shell a lot.
>
> I think there's a clear distinction between value and output for src
> blocks and blurring this distinction for shell src blocks would be
> misleading.  The option to request the output as the outcome of the src
> block is already there.


--
Tim Cross