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Text::Template::LocalVars - Text::Template with localized variables


  use Text::Template::LocalVars 'fill_in_string';

  # store values in 'MyPkg' package
  fill_in_string( $str1, hash => \%vars1, package => 'MyPkg' );

  # use values from MyPkg package, but don't store any new
  # ones there.
  fill_in_string( $str2, hash => \%vars2, package => 'MyPkg',
                  localize => 1 );

  # use the variable package in the last call to a template fill
  # routine in the call stack which led to this code being executed.
  fill_in_string( $str, trackvarpkg => 1 );


Text::Template::LocalVars is a subclass of Text::Template, with additional options to manage how and where template variables are stored. These come in particularly handy when template fragments themselves perform template fills, either inline or by calling other functions which do so.

(Text::Template stores template variables either in a package specified by the caller or in the caller's package. Regardless of where it comes from, for conciseness let's call that package the variable package. Likewise, invoking a template fill function or method, such as fill_in_string, fill_in_file, fill_this_in, or fill_in is called filling, or a fill. )

Text::Template::LocalVars provides the following features:

  • localized variable packages

    The variable package may be cloned instead of being used directly (see "Localized Variable Packages"), providing fills with a sandboxed environment.

  • tracked parent variable packages

    If a fill routine is called without a package name, the package in which the fill routine is invoked is used as the variable package. This works well if the fill routine is invoked in a template fragment, but doesn't if the it is invoked in code compiled in another package (such as a support subroutine). Text::Template::LocalVars keeps track of the appropriate package to use, and can pass that package to the fill routine automatically (see "Tracking Variable Packages").

Localized Variable Packages

Localized variable packages come in handy if your template fragments perform template expansions of their own, and while they should have access to the existing values in the package, you'd prefer they not alter it.

Here's an example:

  use Text::Template::LocalVars 'fill_in_string';
      q[use Text::Template::LocalVars 'fill_in_string';] );

  my $tpl = q[
    { fill_in_string(
                     q[boo + foo = { $boo + $foo }],
                     hash    => { boo => 2 },
                     package => __PACKAGE__,
    foo = { $foo; }
    boo = { $boo; }

      hash    => { foo => 3 },
      package => 'Foo',
      output  => \*STDOUT

We're explicitly specifying a variable package in the outer call to fill_in_string to ensure that we don't contaminate our environment. (See "fill_in_string" for details). In the inner fill_in_string call we use the current variable package so we can see the variables specified in the outer call.

  This outputs

  boo + foo = 5
  foo = 3
  boo = 2

The inner fill sees $foo from the top level fill (as we've specified), and adds $boo to package Foo.

But, what if you don't want to pollute the upper fill's environment? You can't give the inner fill it's own package because it won't see the variables in Foo. You could extract the values from Foo and explicitly pass them to the inner fill, but that is error prone.

With Text::Template::LocalVars, if you pass the localize option, the fill routine gets a copy of the variable package, so it can't contaminate it

  my $tpl = q[{
             q[boo + foo = { $boo + $foo }],
             hash    => { boo => 2 },
             package => __PACKAGE__,
             localize => 1,
  foo = { $foo; }
  boo = { $boo; }

results in

  boo + foo = 5
  foo = 3
  boo =

Certain constructs in packages are not easily copied, so the cloned package isn't identical to the original. The HASH, and ARRAY values in the package are cloned using Storable::dclone; the SCALAR values are copied if they are not references, and the CODE values are copied. All other entries are ignored. This is not a perfect sandbox.

Tracking Variable Packages

If your processing becomes complicated enough that you begin nesting template fills and abstracting some into subroutines, keeping track of variable packages may get complicated. For instance

  sub name {
      my ( $reverse ) = @_;

      my $tpl
        = $reverse
        ? q[ { $last },  { $first } ]
        : q[ { $first }, { $last }  ];

      fill_in_string( $tpl );

  my $tpl = q[
        name = { name( $reverse ) }

      hash => {
          first   => 'A',
          last    => 'Uther',
          reverse => 1,
      package => 'Foo'

Here, we're implementing some complicated template logic in a subroutine, generating a new string with a template fill, and then returning that to an upper level template fragment for inclusion. All of the data required are provided to the top level template fill via the package Foo, but how does that percolate down to the name() subroutine? There are several ways to do this:

  • Explicitly pass the data to name():

      my $tpl = q[
            name = { name( $reverse, $first, $last ) }
  • Explicitly pass the variable package to name():

      my $tpl = q[
            name = { name( $reverse, __PACKAGE__ ) }
  • Turn on variable package tracking in name():

      fill_in_string( $tpl, trackvarpkg => 1 );

    Text::Template::LocalVars keeps track of which variable packages are used in nested calls to fill routines; setting trackvarpkg tells fill_in_string to use the package used by the last fill routine in the call stack which led to this one. In this case, it'll be the one setting package to Foo. If there is none, it falls back to the standard means of determining which package to use.



See "new" in Text::Template.


See "compile" in Text::Template.


The API is the same as in "fill_in" in Text::Template, with the addition of the following options:

  • localize

    If true, a clone of the template variable package is used.

  • trackvarpkg

    If true, and no template variable package is specified, use the one used in the last Text::Template::LocalVars fill routine which led to invoking this one.





The API is the same as See "fill_this_in" in Text::Template, with the addition of the localize and trackvarpkg options (see "fill_in").

If the trackvarpkg option is not set, fill_in_string retains Text::Template::fill_in_string behavior in regards to default variable packages. Unlike other fill routines, Text::Template::fill_in_string will not create an anonymous variable package if one is not specified, but will instead it use the current package. See https://rt.cpan.org/Public/Bug/Display.html?id=51473.


The following are available for export (the same as Text::Template):



Please report any bugs or feature requests to bug-text-template-local at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Text-Template-LocalVars. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.


You can find documentation for this module with the perldoc command.

    perldoc Text::Template::LocalVars

You can also look for information at:


Mark Jason Dominus for Text::Template


Diab Jerius, <djerius at cpan.org>


Copyright (C) 2013 Mark Jason Dominus

Copyright (C) 2014 Smithsonian Astrophysical Observatory

Copyright (C) 2014 Diab Jerius

Text::Template::LocalVars is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

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. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see <http://www.gnu.org/licenses/>.