Is `make-process' doing this?

Is `make-process' doing this?

[Joost Kremers]

Hi all,

just ran into this issue with starting external processes on Linux 
(I can't test if something similar happens on Windows or Mac OS).

Run `emacs -Q', start IELM (for convenience) and type:

IELM> (start-process "some-process" nil "evince" 
"~/path/to/some.pdf")

(Assuming that ~/path/to/some.pdf is an existing pdf file, of 
course). This brings up an evince window with the error message:

Unable to open document "file:///home/joost/~/path/to/some.pdf".

The point is that if I do this from a shell (either some terminal 
emulator, or even eshell or M-x shell in Emacs), it works fine. 
So:

~ $ evince ~/path/to/some.pdf

starts evince and opens the file without issue. 

So I was wondering if it is `make-process' that adds the 
"file:///home/joost/" part, or if it is evince, and if the latter, 
if there is something about `make-process' that keeps evince from 
recognising the argument as an absolute path inspite of the fact 
that it starts with a tilde.

More importantly, I was wondering if I should file a bug report or 
whether this is simply not guaranteed to work. (I modified my code 
to ensure that file names are always expanded with 
`expand-file-name' before being passed to `start-process'. Perhaps 
I should have been doing that all along.)

TIA


-- 
Joost Kremers
Life has its moments

Re: Is `make-process' doing this?

[Andreas Schwab]

On Okt 16 2016, Joost Kremers <joostkremers@fastmail.fm> wrote:

> IELM> (start-process "some-process" nil "evince" "~/path/to/some.pdf")

This passes the string "~/path/to/some.pdf" as the argument.

> ~ $ evince ~/path/to/some.pdf

Try this instead:

$ evince '~/path/to/some.pdf'

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: Is `make-process' doing this?

[Joost Kremers]

On Sun, Oct 16 2016, Andreas Schwab wrote:
> On Okt 16 2016, Joost Kremers <joostkremers@fastmail.fm> wrote:
>
>> IELM> (start-process "some-process" nil "evince" 
>> "~/path/to/some.pdf")
>
> This passes the string "~/path/to/some.pdf" as the argument.
>
>> ~ $ evince ~/path/to/some.pdf
>
> Try this instead:
>
> $ evince '~/path/to/some.pdf'

Thanks for the hint. I'll go find myself a cluebat.

-- 
Joost Kremers
Life has its moments

Re: Is `make-process' doing this?

[Eli Zaretskii]

> From: Joost Kremers <joostkremers@fastmail.fm>
> Date: Sun, 16 Oct 2016 21:02:55 +0200
> 
> Run `emacs -Q', start IELM (for convenience) and type:
> 
> IELM> (start-process "some-process" nil "evince" 
> "~/path/to/some.pdf")
> 
> (Assuming that ~/path/to/some.pdf is an existing pdf file, of 
> course). This brings up an evince window with the error message:
> 
> Unable to open document "file:///home/joost/~/path/to/some.pdf".
> 
> The point is that if I do this from a shell (either some terminal 
> emulator, or even eshell or M-x shell in Emacs), it works fine. 
> So:
> 
> ~ $ evince ~/path/to/some.pdf
> 
> starts evince and opens the file without issue. 

Because the shell expands the tilde.  See the hint from Andreas.

> So I was wondering if it is `make-process' that adds the 
> "file:///home/joost/" part, or if it is evince, and if the latter, 
> if there is something about `make-process' that keeps evince from 
> recognising the argument as an absolute path inspite of the fact 
> that it starts with a tilde.

Neither 'start-process' nor 'make-process' can expand arguments via
'expand-file-name', because they simply don't know which arguments are
file names and which aren't, with the single exception: the program's
executable file name.  So it's up to your code to do that for any
other arguments that you know are file names.