IO::Capture(3pm)

💖 IO::Capture — the perl man page, but make it cute 💖

ok so bestie, buckle UP 🎀 this is IO::Capture(3pm) from the User Contributed Perl Documentation, and it is literally the blueprint page. it's the abstract base class energy. no cap.

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✨ NAME ✨

IO::Capture — Abstract Base Class to build modules to capture output. it's giving foundation, it's giving build on me, periodt. 💅

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🌸 DESCRIPTION 🌸

so the IO::Capture module defines an abstract base class that you can use to build modules that capture output being sent on a filehandle, like STDOUT or STDERR. iconic behaviour honestly. ✨

several modules that come with the distribution do exactly that. i.e., capture STDOUT and STDERR. also go look at James Keenan's IO::Capture::Stdout::Extended on CPAN — that one's a whole vibe too. 🦋

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

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💅 METHODS 💅

these are the methods defined in the IO::Capture Module. this page is discussing the module from the point of view of someone who wants to build a sub-class of IO::Capture. so like, you're the architect bestie. 🫶

each method defined in IO::Capture defines a public method, that then calls one or more private methods. (names starting with an underscore.) this lets you override methods at a finer level of granularity, re-using as much of the functionality provided in the module as possible. chef's kiss architecture tbh.

of these internal methods, three are abstract methods that you will have to override if you want your module to do anything at all. the three are _start(), _retrieve_captured_text(). and _stop(). yes the punctuation is like that. not me noticing it. 💀

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. so thoughtful of them fr fr. 🎀

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. ✨

warning bestie: start cannot be called if there is already a capture in progress. the stop must be called first. do not skip this. 🙈

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. very "check yourself before you wreck yourself" of you. 💅

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 any 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. so like, it's the chill one. 😌

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. literally the main character of retrieval. 👑

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🌈 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. no harm in shopping around bestie 🛍️✨

• 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

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🧚 See Also 🧚

IO::Capture::Overview

IO::Capture::Stdout

IO::Capture::Stderr

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👑 AUTHORS 👑

Mark Reynolds reynolds<at>sgi.com

Jon Morgan jmorgan<at>sgi.com

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💖 MAINTAINED 💖

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

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🌸 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.

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ok that's the whole thing, and that was literally the entire page fr fr 💅✨

signing off with the footer deets so you always know where this came from: this page ships with perl v5.36.0, dated 2022-10-13, under the name IO::Capture(3pm). slay, go build your sub-class bestie 🎀🫶💜