Re: Sus behaviour when cmd string ends with single backslash

[Alex fxmbsw7 Ratchev]

i like the currently showed behavior of '\' parsed as arg
no need to error .. if u meant that, ..

On Mon, Feb 14, 2022 at 11:17 PM Chet Ramey <chet.ramey@case.edu> wrote:

> On 2/13/22 3:15 PM, vzvzvz2@gmail.com wrote:
>
> > Bash Version: 5.0
> > Patch Level: 17
> > Release Status: release
> >
> > Description:
> >
> > Background
> > ----------
> >
> > Commit a0c0a00fc419b7bc08202a79134fcd5bc0427071 (bash-4.4) introduced a
> change in parse.y with following documentation in the change logs:
> >
> > parse.y
> >       - shell_getc: if bash is reading input from a string that ends
> with an
> >         unquoted backslash, add another backslash instead of a newline,
> since
> >         the backslash and newline will disappear in normal processing.
> Fixes
> >         bug with `bash -c 'eval \\; echo y' ' skipping the eval command
> and
> >         setting incorrect exit status, and `bash -ic 'eval \\; echo y' '
> >         seeing EOF on empty line and exiting before the echo.  Keep
> track of
> >         backslash state with last_was_backslash; set in char reading
> loop.
> >         Fixes bug reported by Eduardo A. Bustamante López <
> dualbus@gmail.com>
> >
> > The new code in parse.y
> >
> >         /* Don't add a newline to a string that ends with a backslash if
> we're
> >            going to be removing quoted newlines, since that will eat the
> >            backslash.  Add another backslash instead (will be removed by
> >            word expansion). */
> >         if (bash_input.type == st_string && expanding_alias() == 0 &&
> last_was_backslash && c == EOF && remove_quoted_newline)
> >           shell_input_line[shell_input_line_len] = '\\';
> >         else
> >           shell_input_line[shell_input_line_len] = '\n';
> >         shell_input_line[shell_input_line_len + 1] = '\0';
> >
> >
> > This specific change is also there in commit
> 0385211bb5cb01e0259c64ec2c5cc6337d4e215c on a development branch.
> >
> > Observed vs. expected behaviour
> > -------------------------------
> >
> > The mentioned bug is indeed fixed by this change. However, in case of
> another edge case following new behaviour is observable:
> >
> >   $ bash -c 'echo \'
> >   \
> >   $ # backslash appears on output
>
> I think the behavior of a word consisting only of a backslash is officially
> unspecified.
>
> It's not a quote character -- there's nothing to quote -- so it's not
> removed by quote removal.
>
> In general, I think it's better to err on the side of preserving output
> here.
>
> Existing shell behavior varies, so you can't really count on anything.
>
> --
> ``The lyf so short, the craft so long to lerne.'' - Chaucer
>                  ``Ars longa, vita brevis'' - Hippocrates
> Chet Ramey, UTech, CWRU    chet@case.edu    http://tiswww.cwru.edu/~chet/
>
>