Text::Embed - Cleanly seperate unwieldy text from your source code
use Text::Embed
use Text::Embed CODE|REGEX|SCALAR
use Text::Embed CODE|REGEX|SCALAR, LIST
Code often requires chunks of text to operate - chunks not large enough to warrant extra file dependencies, but enough to make using quotes and heredocs' ugly.
A typical example might be code generators. The text itself is code, and as such is difficult to differentiate and maintain when it is embedded inside more code. Similarly, CGI scripts often include embedded HTML or SQL templates.
Text::Embed provides the programmer with a flexible way to store these portions of text in their namespace's __DATA__ handle - away from the logic - and access them through the package variable %DATA.
The general usage is expected to be suitable for a majority of cases:
use Text::Embed;
foreach(keys %DATA)
{
print "$_ = $DATA{$_}\n";
}
print $DATA{foo};
__DATA__
__foo__
yadda yadda yadda...
__bar__
ee-aye ee-aye oh
__baz__
woof woof
There are two stages to Text::Embed's execution - corresponding to the first and remaining arguments in its invocation.
use Text::Embed (
sub{ ... }, # parse key/values from DATA
sub{ ... }, # process pairs
... # process pairs
);
...
__DATA__
...
By default, Text::Embed uses similar syntax to the __DATA__ token to seperate segments - a line consisting of two underscores surrounding an identifier. Of course, a suitable syntax depends on the text being embedded.
A REGEX or CODE reference can be passed as the first argument - in order to gain finer control of how __DATA__ is parsed:
use Text::Embed qr(<<<<<<<<(\w*?)>>>>>>>>);
A regular expression will be used in a call to split(). Any
leading or trailing empty strings will be removed automatically.
use Text::Embed sub{$_ = shift; ...}
use Text::Embed &Some::Other::Function;
A subroutine will be passed a reference to the __DATA__ string. It should return a LIST of key-value pairs.
In the name of laziness, Text::Embed provides a couple of predefined formats:
__BAZ__
baz baz baz
__FOO__
foo foo foo
foo foo foo
#define BAZ baz baz baz
#define FOO foo foo foo
foo foo foo
<![BAZ[baz baz baz]]>
<![FOO[
foo foo foo
foo foo foo
]]>
After parsing, each key-value pair can be further processed by an arbitrary number of callbacks.
A common usage of this might be controlling how whitespace is represented in each segment. Text::Embed provides some likely defaults which operate on the hash values only.
If you need more control, CODE references or named subroutines can be invoked as necessary. At this point it is safe to rename or modify keys. Undefining a key removes the entry from %DATA.
For the sake of brevity, consider a module that has some embedded SQL. We can implement a processing callback that will prepare each statement, leaving %DATA full of ready to execute DBI statement handlers:
package Whatever;
use DBI;
use Text::Embed(':default', ':trim', 'prepare_sql');
my $dbh;
sub prepare_sql
{
my ($k, $v) = @_;
if(!$dbh)
{
$dbh = DBI->connect(...);
}
$$v = $dbh->prepare($$v);
}
sub get_widget
{
my $id = shift;
my $sql = $DATA{select_widget};
$sql->execute($id);
if($sql->rows)
{
...
}
}
__DATA__
__select_widget__
SELECT * FROM widgets WHERE widget_id = ?;
__create_widget__
INSERT INTO widgets (widget_id,desc, price) VALUES (?,?,?);
..etc
Notice that each pair is passed by reference.
Several utility functions are available to aid implementing custom processing handlers. These are not exported into the callers namespace.
The first are equivalent to the default processing options:
use Text::Embed(':default',':trim');
use Text::Embed(':default', sub {Text::Embed::trim($_[1]);} );
use Text::Embed(':default',':compress');
use Text::Embed(':default', sub {Text::Embed::compress($_[1]);} );
use Text::Embed(':default',':block-indent');
use Text::Embed(':default', sub {Text::Embed::block($_[1]);} );
If a true value is passed as the second argument, then shared indentation is removed, ie :block-noindent.
If comments would make your segments easier to manage, Text::Embed provides defaults handlers for stripping common comment syntax - :strip-perl, :strip-c, :strip-cpp, :strip-xml.
use Text::Embed(':default',':strip-c');
use Text::Embed(':default', sub {Text::Embed::strip($_[1], '/\*', '\*/');} );
Strips all sequences between second and third arguments. The default arguments are '#' and '\n' respectively.
Typically, embedded text may well be some kind of template. Text::Embed
provides rudimentary variable interpolation for simple templates.
The default variable syntax is of the form $(foo):
my $tmpl = "Hello $(name)! Your age is $(age)\n";
my %vars = (name => 'World', age => 4.5 * (10 ** 9));
Text::Embed::interpolate(\$tmpl, \%vars);
print $tmpl;
Any interpolation is done via a simple substitution. An additional
regex argument should accomodate this appropriately, by capturing
the necessary hashkey in $1:
Text::Embed::interpolate(\$tmpl, \%vars, '<%(\S+)%>');
The most likely bugs related to using this module should manifest
themselves as bad key/value error messages. There are two related
causes:
split() is
likely to fail if comments precede the first segment. Comments should
exist in the body of a segment - not preceding it.
split() - particularly if your syntax
wraps your data. Consider using a subroutine for anything non-trivial.
If you employ REGEX parsers, use seperators that are significantly different - and well spaced - from your data, rather than relying on complicated regular expressions to escape pathological cases.
Bug reports and suggestions are most welcome.
Copyright (C) 2005 Chris McEwan - All rights reserved.
Chris McEwan <mcewan@cpan.org>
This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.