NAME Data::Tubes - Text and data canalising VERSION This document describes Data::Tubes version 0.734. SYNOPSIS use Data::Tubes qw< pipeline >; my $id = 0; my $tube = sequence( # automatic loading for simple cases 'Source::iterate_files', # plugin to handle input files 'Reader::by_line', # plugin to read line by line 'Parser::hashy', # plugin to parse hashes # some operations will require some explicit coding of a tube # which is a sub ref with a contract on the return value sub { my $record = shift; $record->{structured}{id} = $id++; return $record; }, # automatic loading, but with arguments [ # plugin to render stuff using Template::Perlish 'Renderer::with_template_perlish', template => "[% a %]:\n id: [% id %]\n meet: [% b %]\n", ], [ # plugin to write stuff into output files, flexibly 'Writer::to_files', filename => \*STDOUT, header => "---\n", footer => "...\n" ], # options for pipeline, in this case just pour into the sink {tap => 'sink'} ); my $input = <<'END'; a=Harry b=Sally a=Jekyll b=Hide a=Flavio b=Silvia a=some b=thing END $tube->([\$input]); ############################################################### # a somewhat similar example, with different facilities use Data::Tubes qw< drain summon >; # load components from relevant plugins summon( qw< +Plumbing::sequence +Source::iterate_files +Reader::read_by_line +Parser::parse_hashy +Renderer::render_with_template_perlish +Writer::write_to_files > ); # define a sequence of tubes, they're just a bunch of sub references my $sequence = sequence( iterate_files(files => [\"n=Flavio|q=how are you\nn=X|q=Y"]), read_by_line(), parse_hashy(chunks_separator => '|'), render_with_template_perlish(template => "Hi [% n %], [% q %]?\n"), write_to_files(filename => \*STDOUT), ); # run it, forget about what comes out of the end drain($sequence); DESCRIPTION This module allows you to define and manage tubes, which are transformation subroutines over records. NOTE: this software is usable but still in a state of flux with respect to the interface. Most notably, although the provided plugins are mostly stable, the accepted parameters' names might change to gain greater consistency across the whole codebase. As an example, passing options to sub-module foo might be done via option foo_opt in one function, and via option opts_for_foo in another, which is ugly and likely to be changed to have only one single way. First Things First: What's a Tube? A sort of operative definition in code: my @outcome = $tube->($input_record); if (scalar(@outcome) == 0) { print "nothing came out, input record was digested!\n"; } elsif (scalar(@outcome) == 1) { my $output_record = shift @outcome; } else { my ($type, $value) = @outcome; if ($type eq 'records') { my @output_records = @$value; } elsif ($type eq 'iterator') { while (my ($output_record) = $iterator->()) {} } else { die "sorry, this tube's output was not valid!\n"; } } A tube is a reference to a subroutine that accepts a single, scalar $input_record and can return zero, one or two (or more) values. In particular: * if it returns zero values, then the tube just hasn't anything to emit for that particular input record. The reasons depend on the tube, but this is a perfectly valid outcome; * if it returns one single value, that is the $output_record corresponding to the $input_record. This is probably the most common case; * if it returns two (or more) values, the first one will tell you what is returned (i.e. its type, and the second will be some way to get the return value(s). This is what you would use if a single $input_record can potentially give birth to multiple output records, like this: * if you can/want to compute all the output records right away (e.g. you just to need to split something in the input record), you can use records for type and pass a reference to an array as the second output value (each of them will be considered an output record); * if you cannot (or don't want to) compute all the output records, e.g. because they might just blow out your process' memory, you can use type iterator and return a subroutine reference back. This subroutine MUST be such that repeatingly calling it can yield two possible results: * one single element, that is the next output record, OR * the empty list, that signals that the iterator has been emptied. This is all that is assumed about tubes in the general case. Some plugins will make further assumptions about what's expected as an input record (e.g. a hash reference in most of the cases) or what is provided as output records, but the generic case is all in the above definition. A few examples will help at this point. A simple filter tube This is probably the most common type of tube: one record comes in, one comes out. In the example, we will assume the input record is a string, and will transform sequences of spacing characters into single spaces: my $tube = sub { my $text = shift; $text =~ s{\s+}{ }gmxs; return $text; }; A grep-like tube This is a tube that might potentially digest the input record, providing nothing out. In the example, we will assume that we're focusing on valid non-negative integers only, and we will ignore everything else: my $tube = sub { my $number = shift; # caution! A simple "return" is much more different than # "return undef", the first one is what we need to provide # "nothing" as output in the list context! return unless defined $number; # ignore input undef:s return unless $number =~ m{\A (?: 0 | [1-9]\d* ) \z}mxs; # this record passed all check, let's return it return $number; }; A few little children out of your input This is a tube that will typically generate a few output records from an input one. It's best suited to be used when you know that you have control over the number of output records, and they will not make your memory consumption explode. In the example, we will provide "words" from a text as output records: my $tube = sub { my $text = shift; my @words = split /\W+/mxs, $text; return (records => \@words); }; Turning a filename into lines This is a tube that might generate a lot of records out of a single input one, so it's your best choice when you don't feel too confortable with using the records alternative above. In the example, we will turn an input file name into a sequence of lines from that file: my $tube = sub { my $filename = shift; open my $fh, '<', $filename or die "open('$filename'): $!"; # the iterator is a reference to a sub, no input parameters my $iterator = sub { my ($line) = <$fh> or return; return $line; }; }; How Can Data::Tubes Help Me Then? Data::Tubes can help you out in different ways: * it provides you with a definition of tube (i.e. a transforming function) that will help you control what you're doing. We already talked about this format, just take a look at "First Things First: What's a Tube?" * it gives you some plumbing facilities to easily perform some common actions over tubes, e.g. put them in sequence or dispatch an input record to the right tube. This is the kind of stuff that you can find in Data::Tubes::Plugin::Plumbing; * it gives you a library of pre-defined tube types that will help you with common tasks related to transforming input data in output data (e.g. in some kind of Extract-Transform-Load process). This is what you can find in the Data::Tubes::Plugin namespace! This module provides you a few useful facilities to make using tubes easier. In particular: * most of the times you should be interested into "pipeline", as it will help you building a sequence of tubes and manage the output of the overall sequence automatically (e.g. just drain it into the sink, after all records have been processed by the different tubes in the sequence; * if for some reason you need to load a tube's factory, you can use "summon", that basically does what import usually does, but with some additional DWIM-mery; * if you have a tube and you want to call it on some input, but you don't care about what will get out, you can use "drain". This is particularly useful if you know (or suspect) that the tube will return an iterator (like a sequence in Data::Tubes::Plugin::Plumbing) because "drain" will ensure that the iterator is run until it is exhausted. FUNCTIONS drain drain($tube, @tube_inputs); drain whatever comes out of a tube. The tube is run with the provided inputs, and if an iterator comes out of it, it is repeatedly run until it provides no more output records. This is useful if the tube returns an iterator, as it will be exhausted. Returns different things depending on the calling context: * in void context, nothing is returned; * in scalar context, different things are returned depending on what the $tube returns. If it returns a single item (i.e. a record), it is returned back. If it returns the string records and an array reference, the array reference is returned. If it returns an iterator, an array reference with all the output records produced by the iterator is returned; * In list context, it always returns a sequence of output records. Note that the scalar context requires you to know precisely what your tube provides back, otherwise you might not know if what you are getting back is a single record or an array reference with the records inside. pipeline $pl = pipeline(@tubes); # OR $pl = pipeline(@tubes, \%args); build up a pipeline (sequence) of @tubes, possibly with options in %args. This is actually only little more than a wrapper around sequence in Data::Tubes::Plugin::Plumbing. The @tubes are passed to sequence (see Data::Tubes::Plugin::Plumbing) as parameter tubes. Basically, Each item in it must be either a tube itself or something that can be transformed into a tube via "tube" below. An optional last parameter allows you to specify additional options: pump set a sub ref that will be called on the output stream from the sequence. In particular, the output iterator from the sequence is repeatedly called to get an output record, and this record is fed into the pump sub ref. tap set to either an allowed string or to a subroutine ref. In the second case, the output iterator will be fed into the provided subroutine reference, that will have to use it as it sees fit. Note that this tap will always be provided with an iterator, which means that it MUST be exhausted in order to actually make the whole pipeline work. You can also set this to one of the allowed strings, which will generate a suitable tap for you: sink this allows you to exhaust the iterator tossing the outcoming records away. This is what you usually want in some *outer* pipeline, when you are not interested in the records that go out of the pipeline because... you already did all that you needed to do; bucket available as of release 0.732, transforms the input iterator into one of the other allowed return values for a valid tube (i.e. the empty list, a single output record, or a string `records` followed by an array reference holding the output records). This is useful if you are interested into what goes out of the pipeline, but you don't want the delayed processing provided by the iterator. If tap is present, pump is ignored. The returned value is always a subroutine reference. If neither tap nor pump are present, the returned sub reference is a tube resulting from the sequence or provided tubes, so you can use it as any other tube. Otherwise, the returned sub reference will take care of invoking the sequence for you with the parameters you provide, and will then pass the iterator to the provided tap/pump as explained above. Examples (the following alternatives all do the same thing, mostly): # no options, what comes back is just a plain tube $sequence = pipeline($tube1, $tube2, $tube3); (undef, $it) = $sequence->($record); # so far, nothing really happened because we have to run # the iterator until it's exhausted while (my ($record) = $it->()) { ... } # set a "sink" tap, we don't care about returned records $handler = pipeline($tube1, $tube2, $tube3, {tap => 'sink'}); $handler->($record); # this will exhaust the iterator # set an explicit tap $handler = pipeline( $tube1, $tube2, $tube3, { tap => sub { my $iterator = shift; while (my ($record) = $iterator->()) { ... } } } ); $handler->($record); # the tap will exhaust the iterator # set a pump $handler = pipeline( $tube1, $tube2, $tube3, { pump => sub { my $record = shift; ... } } ); $handler->($record); # the pump will exhaust the iterator summon # Direct function import summon('Some::Package::subroutine'); # DWIM, treat 'em as plugins under Data::Tubes::Plugin summon( [ qw< +Plumbing sequence logger > ], '+Reader::read_by_line', \%options, ); summon operations, most likely from plugins. This is pretty much the same as a regular import done by use, only supposed to be easier to use in a script. You can pass different things: array references the first item in the array will be considered the package name, the following ones sub names inside that package; strings this will be considered a fully qualified sub name, i.e. including the package name at the beginning. The package name will be subject to some analysis that will make using it a bit easier, by means of resolve_module in Data::Tubes::Util. In particular: * if the name of the package starts with an exclamation point !, this initial character will be stripped away and the rest will be used as the package name; * otherwise, if the package name starts with a plus sign +, this first character will be stripped away and the prefix in the provided options will be used (defaulting to Data::Tubes::Plugin) * otherwise, if the package name does not contain sub-packages (i.e. the sequence ::), then the prefix will be used as in the previous bullet; * otherwise, the provide name is used straight. Examples (in the same order as the bullet above): !SimplePack --> SimplePack +Some::Pack --> Data::Tubes::Plugin::Some::Pack SimplePack --> Data::Tubes::Plugin::SimplePack Some::Pack --> Some::Pack You can optionally pass a hash reference with options as the last parameter, with the following options: package the package where the loaded sub should be imported. Defaults to the package calling the summon function; prefix the prefix to apply when needed. Defaults to Data::Tubes::Plugin. Note that you MUST NOT put the ::, it will be added automatically. tube $tube = tube($factory_locator, @parameters); # OR $tube = tube(\@factory_locator, @parameters); # OR this allows you to facilitate the creation of a tube, doing most of the heavy-lifting automatically. The first parameter is used as a locator of a factory method to generate the real tube. It can be either a string, or an array reference containing two elements, a package name and a subroutine name inside that package. The function load_sub in Data::Tubes::Util is used to load the factory method automatically, which means that the package name is subject to the same rules described in "summon" above. After the factory function is loaded, it is called with the provided @parameters and the returned value... returned back. Hence, this is a quick way to load some factory from a plugin and call it in one, single call: # no additional parameters $files = tube('Reader::iterate_files'); # set some parameters for iterate_files $files = tube('Reader::iterate_files', binmode => ':raw'); Most of the times, you are probably looking for "pipeline" above, as that will eventually call tube automatically. BUGS AND LIMITATIONS Report bugs through GitHub (patches welcome) at https://github.com/polettix/Data-Tubes. AUTHOR Flavio Poletti COPYRIGHT AND LICENSE Copyright (C) 2016 by Flavio Poletti This module is free software. You can redistribute it and/or modify it under the terms of the Artistic License 2.0. This program is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose.