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.
>