Re: [RFAv2 4/6] Implement | (pipe) command.

[Pedro Alves <palves@redhat.com>]

On 5/4/19 7:24 AM, Philippe Waroquiers wrote:
> On Fri, 2019-05-03 at 19:59 +0100, Pedro Alves wrote:
>> On 4/26/19 9:11 PM, Philippe Waroquiers wrote:
>>> The pipe command allows to run a GDB command, and pipe its output
>>> to a shell command:
>>>   (gdb) help pipe
>>>   Send the output of a gdb command to a shell command.
>>>   Usage: pipe [COMMAND] | SHELL_COMMAND
>>>   Usage: | [COMMAND] | SHELL_COMMAND
>>>   Usage: pipe -dX COMMAND X SHELL_COMMAND
>>>   Usage: | -dX COMMAND X SHELL_COMMAND
>>>   Executes COMMAND and sends its output to SHELL_COMMAND.
>>>   If COMMAND contains a | character, the option -dX indicates
>>>   to use the character X to separate COMMAND from SHELL_COMMAND.
>>>   With no COMMAND, repeat the last executed command
>>>   and send its output to SHELL_COMMAND.
>>>   (gdb)
>>
>> I think that making "-dX" a single character is a mistake.  I'd rather
>> make that "-d STRING", so you can use use a string that is much less
>> likely to conflict.  Like bash herestrings.  So a user would be able
>> to do:
>>
>> pipe -d XXXYYYXXX $command | $shell_command
>>
>> I also think "-dX" without a space in between is very non-gdb-ish.
>> In gdb, you kind of either have "-OPT X", or "/OX", which is kind of
>> double "--" vs "-" with getopt, except with different leading
>> tokens.
> 
> Ok, will change to -d STRING.
> 

Thanks.

>>> For example:
>>>   (gdb) pipe print some_data_structure | grep -B3 -A3 something
>>>
>>> The pipe character is defined as an alias for pipe command, so that
>>> the above can be typed as:
>>>   (gdb) | print some_data_structure | grep -B3 -A3 something
>>>
>>
>> I get that "it makes sense", but do you see yourself using the "|" command
>> in preference to "pipe"?  "pipe" can be typed as "pi", which is two
>> key strokes as well.  Kind of wondering whether the character could be
>> saved for something else in the future.  I don't have a use in mind,
>> just thinking out loud.
> Yes, I always use "|" (I even just checked the test to be sure that I
> also tested "pipe" and not only "|").
> pip must be used, as pi launches an interactive python.
> 
> Also, "|" allows to do:
> (gdb) some_command
> ...
> (gdb) ||grep something_in_some_command_output
> (gdb) ||tee save_some_command_output
> 
> which is better than
> (gdb) pip|grep something_in_some_command_output

Alright, that does sound clever.

Thanks,
Pedro Alves