Re^2: Problem with 'system' function in Windows Vista

[diotalevi]

Since this is Windows you might as well say system( "@commands" ) because that's what's really happening anyway. At least its clear then that everything in @commands has to be properly shell quoted.

[ikegami]

Yes and no.

• No, system does quote (in ActivePerl, at least).

  @cmd = ( 'echo', 'identifier', 'a string', '"pre quoted"' );
  system(@cmd);  # identifier "a string" "pre quoted"
  
  $cmd = "@cmd";
  system($cmd);  # identifier a string "pre quoted"
  

• Yes, sending the command as a string instead of a list of arguments is a good idea in Windows. In Windows, command line parsing is done by the child. That means every program has its own mechanism to quote and escape its parameters (*). In turn, that means that system (or the underlying library) must guess at how the child wants its arguments quoted and escaped.

  Avoid the guessing if possible and provide to the child what the child will receive.

* — If any! When quoting is supported, it's usually double quotes. As for an escaping mechanism, I don't remember ever seeing one, so good luck trying to pass a double quote to a program...

[diotalevi]

Escaping, when possible was usually just another doublequote: "bar ""baz" -> bar " baz.

[tye]

The documented MS C RTL quoting rules (that not all Win32 programs follow, unfortunately) say that to get <bar " baz> you should write <"bar \" baz">. The implementation is a bit weird, especially if you don't follow those rules. But your case doesn't work for me:

C:\> perl -le"print '<',$_,'>' for @ARGV" "foo "" bar"
<foo ">
<bar>

C:\>

Note that \ only "escapes" when in a construct matching /\\+"/ (an even number of backslases results in $n-1 backslashes, an odd number in $n-1 backslashes followed by a quote).

This pointed out a subtle bug in the "current" Perl quoting that is done:

system(
    $^X,
    '"-leprint qq(<$_>) for @ARGV"',
    "\\root\\subdir\\",
    "\\root dir\\sub dir\\",
);

produces:

<\root\subdir\>
<\root dir\sub dir">

The fact that I had to quote and be careful with that second argument is the not-subtle short-coming. But the fix for it also fixes the final \ turning into a ".