NAME

       "IO::Capture" - Abstract Base Class to build modules to capture output.

DESCRIPTION

       The "IO::Capture" Module defines an abstract base class that can be used to build modules
       that capture output being sent on a filehandle such as STDOUT or STDERR.

       Several modules that come with the distribution do just that.  I.e., Capture STDOUT and
       STDERR.   Also see James Keenan's "IO::Capture::Stdout::Extended" on CPAN.

       See IO::Capture::Overview for a discussion of these modules and examples of how to build a
       module to sub-class from "IO::Capture" yourself.   If after reading the overview, you
       would like to build a class from "IO::Capture", look here for details on the internals.

METHODS

       These are the methods defined in the "IO::Capture" Module.  This page will be discussing
       the module from the point of view of someone who wants to build a sub-class of
       "IO::Capture".

       Each method defined in the "IO::Capture" Module defines a public method, that then calls
       one or more private methods.  (Names starting with an underscore)  This allows you to
       override methods at a finer level of granularity, re-using as much of the functionality
       provided in the module as possible.

       Of these internal methods, three are abstract methods that your will have to override if
       you want your module to do anything.  The three are "_start()",
       "_retrieve_captured_text()".  and "_stop()".

       Below are the public methods with the private methods that each uses immediately
       following.

   new
       The "new" method creates a new "IO::Capture" object, and returns it to its caller.  The
       object is implemented with a hash.  Each key used by "IO::Capture" is named with the class
       name.  I.e., 'IO::Capture::<key_name>'.  This is to prevent name clashes with keys added
       by sub-class authors.  Attributes can be set in the object by passing a hash reference as
       a single argument to new().

           my $capture = IO::Capture->new( { Key => 'value' } );

       All elements from this hash will be added to the object, and will be available for use by
       children of IO::Capture.

           my $key = $self->{'Key'};

       The internal methods used are:

       "_initialize()"
           "_initialize" is called as soon as the empty object has been blessed.  It adds the
           structure to the object that it will need.  The "IO::Capture" module adds the
           following

               IO::Capture::messages      => []
               IO::Capture::line_pointer  =>  1
               IO::Capture::status        =>  'Ready',  # Busy when capturing

   start
       The "start" method is responsible for saving the current state of the filehandle and or
       signal hander, and starting the data capture.

       Start cannot be called if there is already a capture in progress.  The "stop" must be
       called first.

       These internal methods are called in this order.

       "_check_pre_conditions"
           "_check_pre_conditions" is used to make sure all the preconditions are met before
           starting a capture. The only precondition checked in "IO::Capture", is to insure the
           "Ready" flag is "on".  I.e., There is not already a capture in progress.

           If your module needs to make some checks, and you override this method, make sure you
           call the parent class "_check_pre_conditions" and check the results.

               sub _check_pre_conditions {
                   my $self = shift;

                   return unless $self->SUPER::_check_pre_conditions;

           An example of something you might want to check would be, to make sure STDERR is not
           already tied if you are going to be using "tie" on it.

           Must return a boolean true for success, or false for failure.  If a failure is
           indicated, an "undef" will be returned to the calling function, and an remaining
           private methods for "start" will not be run.

       "_save_current_configuration()"
           "_save_current_configuration" in "IO::Capture" will save the state of "STDERR",
           "STDOUT", and $SIG{__WARN__}.  They are saved in the hash keys
           'IO::Capture::stderr_save', 'IO::Capture::stdout_save', and
           'IO::Capture::handler_save'.

               # Save WARN handler
               $self->{'IO::Capture::handler_save'} = $SIG{__WARN__};
               # Dup stdout
               open STDOUT_SAVE, ">&STDOUT";
               # Save ref to dup
               $self->{'IO::Capture::stdout_save'} = *STDOUT_SAVE;
               # Dup stderr
               open STDERR_SAVE, ">&STDOUT";
               # Save ref to dup
               $self->{'IO::Capture::stderr_save'} = *STDERR_SAVE;

           These saved values can be used in the "_stop" method to restore the original value to
           any you changed.

               $SIG{__WARN__} = $self->{'IO::Capture::handler_save'};
               STDOUT = $self->{'IO::Capture::stdout_save'};
               STDERR = $self->{'IO::Capture::stderr_save'};

           Must return a boolean true for success, or false for failure.  If a failure is
           indicated, an "undef" will be returned to the calling function.

       "_start"
           Start the capture!  This is only an abstract method in "IO::Capture".  It will print a
           warning if called.  Which should not happen, as the author of the sub-class will
           always be sure to override it with her/his own.  :-)

           This is the first of the three you need to define.  You will likely use tie here.  The
           included module "IO::Capture:STDx" (see IO::Capture::STDx or other module of your own
           or from CPAN.  You will read it from the tied module and put it into the object in
           "_retrieve_captured_text".  See _retrieve_captured_text

           Must return a boolean true for success, or false for failure.  If a failure is
           indicated, an "undef" will be returned to the calling function.

   stop
       Stop capturing and return any filehandles and interrupt handlers that were changed, to
       their pre-start state.  This must be called before calling "read()".  If you are looking
       for a way to interact with the process on the other side of the filehandle, take a look at
       the "Other Modules on CPAN".

       Must return a boolean true for success, or false for failure.  If a failure is indicated,
       an "undef" will be returned to the calling function.

       "_retrieve_captured_text()"
           Copy any text captured into the object here.  For example, The modules in this package
           tie the filehandle to the (included) "IO::Capture::STDx" to collect the text.  The
           data needs to be read out of the tied object before the filehandle is untied, so that
           is done here.  In short, if you need to do any work before "_stop" is called, do it
           here.  The "_retrieve_capture_text" in this base class just returns true without doing
           anything.

           Must return a boolean true for success, or false for failure.  If a failure is
           indicated, an "undef" will be returned to the calling function.  The "_stop" internal
           method will be called first.

       "_stop"
           Do what needs to be done to put things back.  Such as untie filehandles and put
           interrupt handlers back to what they were.  The default "_stop" method defined in
           <IO::Capture> won't do anything, so you should.

           Must return a boolean true for success, or false for failure.  If a failure is
           indicated, an "undef" will be returned to the calling function.

   read
       The "read" method is responsible for returning the data captured in the object.  These
       internal methods will be run, in this order.

       "_read()"
           The internal method used to return the captured text.  If called in list context, an
           array will be returned.  (Could be a lot if you captured a lot) or called in scalar
           context, the line pointed to by the line_pointer will be returned and the line_pointer
           incremented.

Other Modules on CPAN

       If this module is not exactly what you were looking for, take a look at these.  Maybe one
       of them will fit the bill.

       •   IO::Filter - Generic input/output filters for Perl IO handles

       •   Expect - Expect for Perl

       •   Tie::Syslog - Tie a filehandle to Syslog.  If you Tie STDERR, then all STDERR errors
           are automatically caught, or you can debug by Carp'ing to STDERR, etc.  (Good for CGI
           error logging.)

       •   FileHandle::Rollback - FileHandle with commit and rollback

See Also

       IO::Capture::Overview

       IO::Capture::Stdout

       IO::Capture::Stderr

AUTHORS

       Mark Reynolds reynolds<at>sgi.com

       Jon Morgan jmorgan<at>sgi.com

MAINTAINED

       Maintained by Mark Reynolds. reynolds<at>sgi.com

COPYRIGHT

       Copyright (c) 2003      Mark Reynolds and Jon Morgan Copyright (c) 2004-2005 Mark Reynolds
       All Rights Reserved.  This module is free software.  It may be used, redistributed and/or
       modified under the same terms as Perl itself.