[Crash-utility] [PATCH] add option -E for foreach

[qiaonuohan]

Hello Dave,

I have modified my patch. In my opinion, regular expression should not 
mix with other task-identifying arguments, so I made some more modifications

At 2012-2-29 1:01, Dave Anderson wrote:
>
>
> ----- Original Message -----
>> Hello Dave,
>>
>> The patch is used to add a new option, "-E regex", to perform the
>> command(s) on all commands whose names contains a match to "regex".
>> "regex" is interpreted as an POSIX extended regular expression.
>>
>> The new option is helpful when using to search some commands whose names
>> are similar. And I think it is more reliable than "foreach<name>
>> <command>  | grep xxx", for information comes from command may have a
>> match to "xxx".
>>
>> P.S.
>> The patch uses some function defined in regex.h, which is offered by glibc.
>
> The concept is a pretty good idea.  However:
>
> (1) It doesn't work as you've described it in the help page, and
> (2) I don't like the invocation, because option characters are
>      meant to be passed to the selected command, and not for
>      consumption by the foreach command itself.
>
> With respect to (1), your help page example shows this:
>
>    crash>  help foreach
>    ... [ cut ] ...
>    Display the state of tasks whose name contains a match to 'event.*':
>
>      crash>  foreach -E 'event.*' task -R state
>      PID: 99     TASK: ffff8804750d5500  CPU: 0   COMMAND: "events/0"
>        state = 1,
>
>      PID: 100    TASK: ffff8804750d4ac0  CPU: 1   COMMAND: "events/1"
>        state = 1,
>
>      PID: 101    TASK: ffff8804750d4080  CPU: 2   COMMAND: "events/2"
>        state = 1,
>      ...
>
> But your example doesn't work with the encompassing "'" characters:
>
>    crash>  foreach -E 'event.*' task -R state
>    crash>
>
> If I remove the encompassing "'" characters, it does work:
>
>    crash>  foreach -E event.* task -R state
>    PID: 67     TASK: ffff88033833d500  CPU: 0   COMMAND: "events/0"
>      state = 1,
>
>    PID: 68     TASK: ffff88033833cac0  CPU: 1   COMMAND: "events/1"
>      state = 1,
>
>    PID: 69     TASK: ffff88033833c080  CPU: 2   COMMAND: "events/2"
>      state = 1,
>
>    PID: 70     TASK: ffff880338367540  CPU: 3   COMMAND: "events/3"
>      state = 1,
>
>    ...
>
> So apparently regcomp() does not handle strings encompassed with
> the "'" characters.
>
> With respect to (2), however, since the process name option already
> has the "\" invocation option to prevent ambiguity with the foreach
> command name:
>
>    crash>  help foreach
>    ...
>       name  perform the command(s) on all commands with this name.  If the
>             command name can be confused with a foreach command name, then
>             precede the name string with a "\".
>    ...
>
> Perhaps there can be a third way of specifying the "name" option, where a
> regular expression *must* be encompassed by "'" characters, and therefore:
>
>   (a) the argument can be recognized as a POSIX expression, and
>   (b) the encompassing "'" characters can be stripped off before passing the
>       argument string to regcomp().
>
> So then you could simply enter:
>
>    crash>  foreach 'event.*' task -R state
>
> And have it described in the help page something like:
>
>    crash>  help foreach
>    ...
>       name  perform the command(s) on all processes with this name.  If the
>             process name can be confused with a foreach command name, then
>             precede the name string with a "\".  If the process name is
>             enclosed within "'" characters, then the encompassed string
>             is a POSIX extended regular expression that will be used to
>             match process names.
>    ...
>
> Then you can simplify things by replacing the FOREACH_E_FLAG usage with
> a FOREACH_REGEX flag that can be set in cmd_foreach() and checked
> in foreach().
>
> Dave
>
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>
>


-- 
--
Regards
Qiao Nuohan
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