Graham Ollis 🔥🐉
and 4 contributors


String::Template - Fills in string templates from hash of fields


version 0.21


 use String::Template;
 my %fields = ( num => 2, str => 'this', date => 'Feb 27, 2008' );
 my $template = "...<num%04d>...<str>...<date:%Y/%m/%d>...\n";
 print expand_string($template, \%fields);
 #prints: "...0002...this...2008/02/27..."


Generate strings based on a template.



 my $str = expand_string($template, \%fields, $undef_flag);

Fills in a simple template with values from a hash, replacing tokens like "<fieldname>" with the value from the hash $fields->{fieldname}.

Some special characters can be used to impose formatting on the fields:

 % - treat like a sprintf() format
     e.g.  <int%02d>

 : - treat like a L<POSIX::strftime()> format
     e.g. <date:%Y-%m-%d>

 ! - Just like ':', but with gmtime instead of localtime
     e.g. <gmdate!%Y-%m-%d %H:%M>

 # - treat like args to substr()
     e.g. <str#0,2> or <str#4>

For the ':' strftime formats, the field is parsed by Date::Parse, so it can handle any format that can handle.

Handling of undefined fields can be controlled with $undef_flag. If it is false (default), undefined fields are simply replace with an empty string. If set to true, the field is kept verbatim. This can be useful for multiple expansion passes.

The { character is specially special, since it allows fields to contain additional characters that are not intended for formatting. This is specially useful for specifying additional content inside a field that may not exist in the hash, and which should be entirely replaced with the empty string.

This makes it possible to have templates like this:

 my $template = '<name><nick{ "%s"}><surname{ %s}>';

 my $mack = { name => 'Mack', nick    => 'The Knife' };
 my $jack = { name => 'Jack', surname => 'Sheppard'  };

 expand_string( $template, $mack ); # Returns 'Mack "The Knife"'
 expand_string( $template, $jack ); # Returns 'Jack Sheppard'


 my $str = expand_stringi($template, \%fields, $undef_flag);

expand_stringi works just like expand_string, except that tokens and hash keys are treated case insensitively.


 my @missing = missing_values($template, \%fields, $dont_allow_undefs);

Checks to see if the template variables in a string template exist in a hash. Set $dont_allow_undefs to 1 to also check to see if the values for all such keys are defined.

Returns a list of missing keys or an empty list if no keys were missing.


 my $status = expand_hash($hash[, $maxdepth]);

Expand a hash of templates/values. This function will repeatedly replace templates in the values of the hash with the values of the hash they reference, until either all "<>" templates are gone, or it has iterated $maxdepth times (default 10).

Returns undef if there are unexpanded templates left, otherwise true.


String::Format performs a similar function, with a different syntax.


Original author: Brian Duggan

Current maintainer: Graham Ollis <>


Curt Tilmes

Jeremy Mates (thirg, JMATES)

José Joaquín Atria


This software is copyright (c) 2015 by Brian Duggan.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.