Re: [RFA/RFC] Problem with '!' escaping with zsh/bash/ksh

[Joel Brobecker <brobecker at gnat dot com>]

Daniel said:
> By the time it gets to execve, we have:
> execve("/home/drow/foo/foo\\!bar/ls", ["/home/drow/foo/foo\\!bar/ls"],
> 
> i.e. the backslash has been escaped too!

Unfortunately, this is not what's happening:

(top-gdb) p shell_command
$1 = 0xbffff2f0 "exec '/home/brobecke/tmp/GEO_ENV\\!9.159/foo' "

The value printed for shell_command is misleading (the double backslash),
when you dump the memory at the address string, I only see one backslash:

(top-gdb) x /50c 0xbffff2f0
0xbffff2f0:     101 'e' 120 'x' 101 'e' 99 'c'  32 ' '  39 '\'' 47 '/'  104 'h'
0xbffff2f8:     111 'o' 109 'm' 101 'e' 47 '/'  98 'b'  114 'r' 111 'o' 98 'b'
0xbffff300:     101 'e' 99 'c'  107 'k' 101 'e' 47 '/'  116 't' 109 'm' 112 'p'
0xbffff308:     47 '/'  71 'G'  69 'E'  79 'O'  95 '_'  69 'E'  78 'N'  86 'V'
0xbffff310:     92 '\\' 33 '!'  57 '9'  46 '.'  49 '1'  53 '5'  57 '9'  47 '/'
                ^^^^^^^
0xbffff318:     102 'f' 111 'o' 111 'o' 39 '\'' 32 ' '  0 '\0'  -1 'ÿ'  -65 '¿'
0xbffff320:     102 'f' -48 'Ð'

Eli said:
> Are you saying that zsh doesn't support escaping of arbitrary
> characters with a backslash?  That is, under zsh, "\a" is not the same
> as "a"?  I'd be surprised.

If I restrict myself to using a zsh shell alone, outside of GDB, here is
the behavior I get:

    With the backlash:
    % zsh
    % exec '/home/brobecke/tmp/GEO_ENV\!9.159/foo'
    zsh: no such file or directory: /home/brobecke/tmp/GEO_ENV\!9.159/foo
    %

    Without the backslash
    % zsh
    % exec '/home/brobecke/tmp/GEO_ENV!9.159/foo'
    %

I think you are right to say that "\a" is equivalent to "a" in general.
However, in our case, the argument is quoted, specifically single-quoted.
And it seems to make a big difference: with single quotes, the
expression is no longer evaluated. That's why the backslash becomes
harmful.

Daniel said:
> By the way... what would the general reaction be to supporting exec'ing
> the program directly instead of through the shell?  At least as an
> option, since it would be a bit of an interface/quoting change?

I think that'd be very nice, actually. Can somebody tell me what the
advantage of forking via a shell is?

-- 
Joel