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

[Dave Anderson]

----- Original Message -----
> 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

Why not?  It would be far more useful if you could maintain
the current capability of providing a mixture of pid/task/name
task-identifiers along with this new regular-expression-matching
scheme. 

Dave

> 
> 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