Re: [PATCH] main: don't raise exception when executing dotcmd() on a non-existent file

[Antonio Ospite <ao2@xxxxxx>]

On Sat, 24 Nov 2018 18:56:48 +0100
Jilles Tjoelker <jilles@xxxxxxxx> wrote:

> On Sat, Nov 24, 2018 at 05:20:21PM +0100, Antonio Ospite wrote:
> > When sourcing a file with the dotcmd() builtin, dash raises an exception
> > when the input file cannot be opened.
> 
> > For instance the following script fails prematurely and does not output
> > the message:
> 
> >   #!/bin/sh
> 
> >   . /non-existent-file
> >   echo "Survived!"
> 
> > In this case, the behavior of dash is different from other shells (e.g.
> > bash, zsh) which are more forgiving and allow execution to carry on even
> > if the input file cannot be opened.
> 
> POSIX is unambiguous (XCU 2.14 Special Built-In Utilities -> dot) that a
> non-interactive shell shall abort when a dot script is not found, and
> bash and zsh comply to this when standards compliance is requested (e.g.
> by naming the shell "sh" in argv[0] or using "set -o posix" in bash or
> "set -o posixbuiltins" in zsh). Most other shells (e.g. mksh, FreeBSD
> sh, yash) comply to POSIX unconditionally here, like dash currently
> does.
>

OK, thanks for clarifying that.

I guess I was a little lazy for not checking before posting.

> > Fix this by passing the INPUT_NOFILE_OK flag when calling setinputfile()
> > in dotcmd().
> 
> > As a bonus, this also fixes cases like the following:
> 
> >   set -e
> >   . /non-existent-file || true
> >   echo "Survived! Let's do something else..."
> 
> > This idiom is sometimes used in shell script to source a config file
> > with default values only to provide fallback values if the default
> > values were not available.
> 
> The above code is specific to bash and zsh non-POSIX modes, and will not
> work in a #!/bin/sh script unless specific steps are taken (such as "set
> +o posix" or starting the script with "bash script1" rather than
> "./script1").
> 
> The simple solution is
>   [ ! -f /non-existent-file ] || . /non-existent-file
> Time-of-check-time-of-use issues should not be an issue for config
> files.
>

Indeed this is the most used form, thank you again.

Now I know that the other one is non-standard.

Sorry for the noise,
   Antonio

> Alternatively, one could try
>   command . ./non-existent-file || true
> but this may ignore more errors than desired (such as syntax errors in
> the sourced file) and does not work correctly in yash 2.30.
> 
> -- 
> Jilles Tjoelker


-- 
Antonio Ospite
https://ao2.it
https://twitter.com/ao2it

A: Because it messes up the order in which people normally read text.
   See http://en.wikipedia.org/wiki/Posting_style
Q: Why is top-posting such a bad thing?