Since I was overwriting the braces by space character, this could
essentially change a valid gdb command having braces after pipe.
Here is the example:
(gdb) p argc | {int} &argc

I have modified the patch to defer the any overwrite (and essentially
the modification) of actual input string for very last moment when the
a sub-string of a given input in gdb prompt is qualified to be in a
valid format of shell command.

I am re-submitting the patch for review and comments with the
necessary corrections in place. Please do comment on the changes.

 top.c     |   77 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 ui-file.c |   15 ++++++++++++
 ui-file.h |    3 ++
 3 files changed, 94 insertions(+), 1 deletion(-)

Regards,
Abhijit Halder


On Mon, Jul 18, 2011 at 11:31 PM, Abhijit Halder
<abhijit.k.halder@gmail.com> wrote:
> Please don't consider this patch. This has a conflict with following
> syntax of of
> (gdb) p var | {type} address
>
> On Sat, Jul 16, 2011 at 11:35 PM, Abhijit Halder
> <abhijit.k.halder@gmail.com> wrote:
>> A small correction. Re-submitting the patch. The earlier patch was not
>> able to handle below situation:
>> (gdb) p '|' | { less }
>>
>> On Sat, Jul 16, 2011 at 3:38 PM, Abhijit Halder
>> <abhijit.k.halder@gmail.com> wrote:
>>> On Sat, Jul 16, 2011 at 3:17 PM, Eli Zaretskii <eliz@gnu.org> wrote:
>>>>> Date: Sat, 16 Jul 2011 14:12:35 +0530
>>>>> From: Abhijit Halder <abhijit.k.halder@gmail.com>
>>>>>
>>>>> I have implemented a feature which will allow one to pass the output
>>>>> of any gdb command to the shell for further processing.
>>>>
>>>> Thanks.
>>>>
>>>> If this is accepted, we will need a corresponding addition to the
>>>> manual.
>>>>
>>>>> +      for (cpos = spos; (cpos = memchr (cpos, '"', (sh_cmd-cpos))) != NULL; cpos++)
>>>>> +        quote_cnt++;
>>>>> +      spos = (sh_cmd + 1);
>>>>> +      if ((quote_cnt % 2) == 0 || (sh_cmd = strchr (spos, '|')) == NULL)
>>>>> +        break;
>>>>
>>>> I'm not sure I understand this (comments would be helpful).  Are you
>>>> assuming that quote characters `"' in shell commands cannot be
>>>> escaped, e.g. with a backslash?  And what about quoting with a single
>>>> quote character ("'")?
>>>>
>>> Any pipe ('|' character), not within double quote will be considered
>>> as either a bitwise-OR operator or a pipe between gdb and shell.
>>> String after pipe (not within double quote) will be considered as
>>> shell command if (and only if) it is encapsulated within opening and
>>> closing braces ('{' and '}') . The shell command can surely contain
>>> double quote, even braces. There is no validation done for shell
>>> command.
>>>
>>>>> +    if (*cpos != '{')
>>>>> +      return NULL;
>>>>> +
>>>>> +    *cpos = ' ';
>>>>> +
>>>>> +    cpos = epos;
>>>>> +    while (isspace(*cpos))
>>>>> +      cpos--;
>>>>> +
>>>>> +    if (*cpos != '}')
>>>>> +      return NULL;
>>>>
>>>> What is this magic about {...} that you are removing?  Again, comments
>>>> could help.
>>>>
>>> Here I am removing the braces from the shell command. An example will
>>> help in understanding this:
>>> (gdb) thread apply all bt | { grep "foo" }
>>> This will be a valid command. { grep "foo" } will be considered as
>>> shell command and we need to erase the braces part of it to make it a
>>> valid shell command.
>>>>> +
>>>>> +    *cpos = ' ';
>>>>> +    }
>>>>> +
>>>>> +  if (sh_cmd)
>>>>> +    *sh_cmd++ = '\0';
>>>>> +
>>>>> +  return sh_cmd;
>>>>
>>>> This butchers the string passed to execute_command.  Are you sure all
>>>> the callers of execute_command can safely deal with that?  What if the
>>>> string is a constant string, for example?
>>>>
>>> The new code path will be executed only when one will enter a command
>>> containing pipeline between gdb and shell. In that case the string
>>> passed to execute_command must not be a constant string (since it is
>>> user input from gdb prompt). Hence we are safe.
>>>
>>
>