text::template(3)

NAME

Text::Template - Expand template text with embedded Perl

VERSION

This file documents "Text::Template" version 1.43

SYNOPSIS

use Text::Template;
$template = Text::Template->new(TYPE => FILE,  SOURCE  =>
'filename.tmpl');
$template  = Text::Template->new(TYPE => ARRAY, SOURCE =>
[ ... ] );
$template  =  Text::Template->new(TYPE   =>   FILEHANDLE,
SOURCE => $fh );
$template = Text::Template->new(TYPE => STRING, SOURCE =>
'...' );
$template   =   Text::Template->new(PREPEND   =>    q{use
strict;}, ...);
# Use a different template file syntax:
$template  =  Text::Template->new(DELIMITERS  =>  [$open,
$close], ...);
$recipient = 'King';
$text = $template->fill_in();  # Replaces  `{$recipient}'
with `King'
print $text;
$T::recipient = 'Josh';
$text = $template->fill_in(PACKAGE => T);
# Pass many variables explicitly
$hash = { recipient => 'Abed-Nego',
          friends => [ 'me', 'you' ],
          enemies => { loathsome => 'Bill Gates',
                       fearsome => 'Larry Ellison' },
        };
$text = $template->fill_in(HASH => $hash, ...);
# $recipient is Abed-Nego,
# @friends is ( 'me', 'you' ),
# %enemies is ( loathsome => ..., fearsome => ... )
#  Call  &callback  in case of programming errors in template
$text = $template->fill_in(BROKEN => callback, BROKEN_ARG
=> $ref, ...);
# Evaluate program fragments in Safe compartment with restricted permissions
$text = $template->fill_in(SAFE => $compartment, ...);
# Print result text instead of returning it
$success = $template->fill_in(OUTPUT => ILEHANDLE, ...);
# Parse template with different template file syntax:
$text = $template->fill_in(DELIMITERS => [$open, $close],
...);
#  Note  that this is *faster* than using the default delimiters
# Prepend specified perl code  to  each  fragment  before
evaluating:
$text   =   $template->fill_in(PREPEND  =>  q{use  strict
'vars';}, ...);
use Text::Template 'fill_in_string';
$text = fill_in_string( <<EOM, PACKAGE => 'T', ...);
Dear {$recipient},
Pay me at once.
       Love,
        G.V.
EOM
use Text::Template 'fill_in_file';
$text = fill_in_file($filename, ...);
# All templates will always have `use  strict  vars'  attached to all fragments
Text::Template->always_prepend(q{use strict 'vars';});

DESCRIPTION

This is a library for generating form letters, building
HTML pages, or filling in templates generally. A `tem
plate' is a piece of text that has little Perl programs
embedded in it here and there. When you `fill in' a tem
plate, you evaluate the little programs and replace them
with their values.

You can store a template in a file outside your program.
People can modify the template without modifying the pro
gram. You can separate the formatting details from the
main code, and put the formatting parts of the program
into the template. That prevents code bloat and encour
ages functional separation.

Example

Here's an example of a template, which we'll suppose is stored in the file "formletter.tmpl":: Dear {$title} {$lastname},; It has come to our attention that you are delin; quent in your
{$monthname[$last_paid_month]} payment. Please; remit
${sprintf("%.2f", $amount)} immediately, or your; patellae may
be needlessly endangered.

Love,

Mark "Vizopteryx" Dominus
The result of filling in this template is a string, which might look something like this:: Dear Mr. Gates,; It has come to our attention that you are delin; quent in your
February payment. Please remit
$392.12 immediately, or your patellae may
be needlessly endangered.

Love,

Mark "Vizopteryx" Dominus
Here is a complete program that transforms the example template into the example result, and prints it out:: use Text::Template;; my $template = Text::Template->new(SOURCE =>; 'formletter.tmpl')
or die "Couldn't construct template: $Text::Tem

plate::ERROR";; my @monthname = qw(January February March April; May June
July August September October

November December);; my %vars = (title => 'Mr.',
firstname => 'Bill',
lastname => 'Gates',
last_paid_month => 1, # February
amount => 392.12,
monthname => @monthname,; );
my $result = $template->fill_in(HASH => vars);
if (defined $result) { print $result } else { die "Couldn't fill in template: $Text::Tem
plate::ERROR" }
Philosophy
When people make a template module like this one, they almost always start by inventing a special syntax for sub stitutions. For example, they build it so that a string like "%%VAR%%" is replaced with the value of $VAR. Then they realize the need extra formatting, so they put in some special syntax for formatting. Then they need a loop, so they invent a loop syntax. Pretty soon they have a new little template language.
This approach has two problems: First, their little lan guage is crippled. If you need to do something the author hasn't thought of, you lose. Second: Who wants to learn another language? You already know Perl, so why not use it?
"Text::Template" templates are programmed in Perl. You embed Perl code in your template, with "{" at the begin ning and "}" at the end. If you want a variable interpo lated, you write it the way you would in Perl. If you need to make a loop, you can use any of the Perl loop con structions. All the Perl built-in functions are avail able.

Details

Template Parsing

The "Text::Template" module scans the template source. An
open brace "{" begins a program fragment, which continues
until the matching close brace "}". When the template is
filled in, the program fragments are evaluated, and each
one is replaced with the resulting value to yield the text
that is returned.

A backslash " that is in front of a brace) escapes its special meaning. The result of filling out this template:: The sum of 1 and 2 is {1+2}
is: { The sum of 1 and 2 is 3 }
If you have an unmatched brace, "Text::Template" will return a failure code and a warning about where the prob lem is. Backslashes that do not precede a brace are passed through unchanged. If you have a template like this:: { "String that ends in a newline.0 }
The backslash inside the string is passed through to Perl unchanged, so the "0 really does turn into a newline. See the note at the end for details about the way back slashes work. Backslash processing is not done when you specify alternative delimiters with the "DELIMITERS" option. (See "Alternative Delimiters", below.)
Each program fragment should be a sequence of Perl state ments, which are evaluated the usual way. The result of the last statement executed will be evaluted in scalar context; the result of this statement is a string, which is interpolated into the template in place of the program fragment itself.
The fragments are evaluated in order, and side effects from earlier fragments will persist into later fragments:: {$x = @things; ''}The Lord High Chamberlain has; gotten {$x}
things for me this year.
{ $diff = $x - 17;
$more = 'more'
if ($diff == 0) {
$diff = 'no';

} elsif ($diff < 0) {

$more = 'fewer';

}
'';; }
That is {$diff} {$more} than he gave me last year.
The value of $x set in the first line will persist into the next fragment that begins on the third line, and the values of $diff and $more set in the second fragment will persist and be interpolated into the last line. The out put will look something like this:: The Lord High Chamberlain has gotten 42
things for me this year.; That is 25 more than he gave me last year.
That is all the syntax there is.
The $OUT variable
There is one special trick you can play in a template. Here is the motivation for it: Suppose you are going to pass an array, @items, into the template, and you want the template to generate a bulleted list with a header, like this:: Here is a list of the things I have got for you; since 1907:
* Ivory
* Apes
* Peacocks
* ...
One way to do it is with a template like this:: Here is a list of the things I have got for you; since 1907:
{ my $blist = '';
foreach $i (@items) {
$blist .= qq{ * $i0;

}
$blist;; }
Here we construct the list in a variable called $blist, which we return at the end. This is a little cumbersome. There is a shortcut.
Inside of templates, there is a special variable called $OUT. Anything you append to this variable will appear in the output of the template. Also, if you use $OUT in a program fragment, the normal behavior, of replacing the fragment with its return value, is disabled; instead the fragment is replaced with the value of $OUT. This means that you can write the template above like this:: Here is a list of the things I have got for you; since 1907:
{ foreach $i (@items) {
$OUT .= " * $i0;; }
}
$OUT is reinitialized to the empty string at the start of each program fragment. It is private to "Text::Template", so you can't use a variable named $OUT in your template without invoking the special behavior.
General Remarks
All "Text::Template" functions return "undef" on failure, and set the variable $Text::Template::ERROR to contain an explanation of what went wrong. For example, if you try to create a template from a file that does not exist, $Text::Template::ERROR will contain something like:: Couldn't open file xyz.tmpl: No such file or di; rectory
"new": $template = new Text::Template ( TYPE => ...,; SOURCE => ... );
This creates and returns a new template object. "new" returns "undef" and sets $Text::Template::ERROR if it can't create the template object. "SOURCE" says where the template source code will come from. "TYPE" says what kind of object the source is.
The most common type of source is a file:: new Text::Template ( TYPE => 'FILE', SOURCE =>; $filename );
This reads the template from the specified file. The filename is opened with the Perl "open" command, so it can be a pipe or anything else that makes sense with "open".
The "TYPE" can also be "STRING", in which case the "SOURCE" should be a string:: new Text::Template ( TYPE => 'STRING',
SOURCE => "This is the actual

template!" );
The "TYPE" can be "ARRAY", in which case the source should be a reference to an array of strings. The concatenation of these strings is the template:: new Text::Template ( TYPE => 'ARRAY',
SOURCE => [ "This is ", "the

actual",
" template!",

]; );
The "TYPE" can be FILEHANDLE, in which case the source should be an open filehandle (such as you got from the "FileHandle" or "IO::*" packages, or a glob, or a refer ence to a glob). In this case "Text::Template" will read the text from the filehandle up to end-of-file, and that text is the template:: # Read template source code from STDIN:
new Text::Template ( TYPE => 'FILEHANDLE',
SOURCE => TDIN );
If you omit the "TYPE" attribute, it's taken to be "FILE". "SOURCE" is required. If you omit it, the program will abort.
The words "TYPE" and "SOURCE" can be spelled any of the following ways:: TYPE SOURCE
Type Source
type source
-TYPE -SOURCE
-Type -Source
-type -source
Pick a style you like and stick with it.
"DELIMITERS": You may also add a "DELIMITERS" option. If this
option is present, its value should be a reference to
an array of two strings. The first string is the
string that signals the beginning of each program
fragment, and the second string is the string that
signals the end of each program fragment. See "Alter
native Delimiters", below.
"UNTAINT": If your program is running in taint mode, you may have
problems if your templates are stored in files. Data
read from files is considered 'untrustworthy', and
taint mode will not allow you to evaluate the Perl
code in the file. (It is afraid that a malicious per
son might have tampered with the file.); In some environments, however, local files are trust
worthy. You can tell "Text::Template" that a certain
file is trustworthy by supplying "UNTAINT => 1" in the
call to "new". This will tell "Text::Template" to
disable taint checks on template code that has come
from a file, as long as the filename itself is consid
ered trustworthy. It will also disable taint checks
on template code that comes from a filehandle. When
used with "TYPE => 'string'" or "TYPE => 'array'", it
has no effect.; See perlsec for more complete information about taint
ing.; Thanks to Steve Palincsar, Gerard Vreeswijk, and Dr.
Christoph Baehr for help with this feature.
"PREPEND": This option is passed along to the "fill_in" call
unless it is overridden in the arguments to "fill_in".
See ""PREPEND" feature and using "strict" in tem
plates" below.
"BROKEN": This option is passed along to the "fill_in" call
unless it is overridden in the arguments to "fill_in".
See "BROKEN" below.
"compile": $template->compile()
Loads all the template text from the template's source, parses and compiles it. If successful, returns true; oth erwise returns false and sets $Text::Template::ERROR. If the template is already compiled, it returns true and does nothing.
You don't usually need to invoke this function, because "fill_in" (see below) compiles the template if it isn't compiled already.
If there is an argument to this function, it must be a reference to an array containing alternative delimiter strings. See ""Alternative Delimiters"", below.
"fill_in": $template->fill_in(OPTIONS);
Fills in a template. Returns the resulting text if suc cessful. Otherwise, returns "undef" and sets $Text::Tem plate::ERROR.
The OPTIONS are a hash, or a list of key-value pairs. You can write the key names in any of the six usual styles as above; this means that where this manual says "PACKAGE" (for example) you can actually use any of: PACKAGE Package package -PACKAGE -Package -package
Pick a style you like and stick with it. The all-lower case versions may yield spurious warnings about: Ambiguous use of package => resolved to "package"
so you might like to avoid them and use the capitalized versions.
At present, there are eight legal options: "PACKAGE", "BROKEN", "BROKEN_ARG", "SAFE", "HASH", "OUTPUT", and "DELIMITERS".
"PACKAGE": "PACKAGE" specifies the name of a package in which the
program fragments should be evaluated. The default is
to use the package from which "fill_in" was called.
For example, consider this template:

The value of the variable x is {$x}.
If you use "$template->fill_in(PACKAGE => 'R')" , then the $x in the template is actually replaced with the value of $R::x. If you omit the "PACKAGE" option, $x will be replaced with the value of the $x variable in the package that actually called "fill_in".
You should almost always use "PACKAGE". If you don't, and your template makes changes to variables, those changes will be propagated back into the main program. Evaluating the template in a private package helps prevent this. The template can still modify variables in your program if it wants to, but it will have to do so explicitly. See the section at the end on `Secu rity'.
Here's an example of using "PACKAGE":: Your Royal Highness,; Enclosed please find a list of things I have; gotten
for you since 1907:; { foreach $item (@items) {
$item_no++;
$OUT .= " $item_no. $item0;; }
}
Signed, Lord High Chamberlain
We want to pass in an array which will be assigned to the array @items. Here's how to do that:: @items = ('ivory', 'apes', 'peacocks', );
$template->fill_in();
This is not very safe. The reason this isn't as safe is that if you had a variable named $item_no in scope in your program at the point you called "fill_in", its value would be clobbered by the act of filling out the template. The problem is the same as if you had writ ten a subroutine that used those variables in the same way that the template does. ($OUT is special in tem plates and is always safe.)
One solution to this is to make the $item_no variable private to the template by declaring it with "my". If the template does this, you are safe.
But if you use the "PACKAGE" option, you will probably be safe even if the template does not declare its variables with "my":: @Q::items = ('ivory', 'apes', 'peacocks', );
$template->fill_in(PACKAGE => 'Q');
In this case the template will clobber the variable $Q::item_no, which is not related to the one your pro gram was using.
Templates cannot affect variables in the main program that are declared with "my", unless you give the tem plate references to those variables.
"HASH": You may not want to put the template variables into a
package. Packages can be hard to manage: You can't
copy them, for example. "HASH" provides an alterna
tive.; The value for "HASH" should be a reference to a hash
that maps variable names to values. For example,

$template->fill_in(HASH => { recipient => "The

King",
items => ['gold',

'frankincense', 'myrrh']

});
will fill out the template and use "The King" as the value of $recipient and the list of items as the value of @items.
The full details of how it works are a little involved, so you might want to skip to the next sec tion.
Suppose the key in the hash is key and the value is value.
� If the value is "undef", then any variables named: $key, @key, %key, etc., are undefined.
� If the value is a string or a number, then $key is: set to that value in the template.
� If the value is a reference to an array, then @key: is set to that array. If the value is a reference
to a hash, then %key is set to that hash. Simi
larly if value is any other kind of reference.
This means that

var => "foo"
and: var =>
have almost exactly the same effect. (The differ ence is that in the former case, the value is copied, and in the latter case it is aliased.)
Normally, the way this works is by allocating a pri vate package, loading all the variables into the pack age, and then filling out the template as if you had specified that package. A new package is allocated each time. However, if you also use the "PACKAGE" option, "Text::Template" loads the variables into the package you specified, and they stay there after the call returns. Subsequent calls to "fill_in" that use the same package will pick up the values you loaded in.
If the argument of "HASH" is a reference to an array instead of a reference to a hash, then the array should contain a list of hashes whose contents are loaded into the template package one after the other. You can use this feature if you want to combine sev eral sets of variables. For example, one set of vari ables might be the defaults for a fill-in form, and the second set might be the user inputs, which over ride the defaults when they are present:: $template->fill_in(HASH => [defaults, user_in; put]);
You can also use this to set two variables with the same name:: $template->fill_in(HASH => [{ v => "The King"; },
{ v => [1,2,3] },; ]
);
This sets $v to "The King" and @v to "(1,2,3)".
"BROKEN": If any of the program fragments fails to compile or
aborts for any reason, and you have set the "BROKEN"
option to a function reference, "Text::Template" will
invoke the function. This function is called the
"BROKEN" function. The "BROKEN" function will tell "Text::Template" what to do next.; If the "BROKEN" function returns "undef", "Text::Tem
plate" will immediately abort processing the template
and return the text that it has accumulated so far.
If your function does this, it should set a flag that
you can examine after "fill_in" returns so that you
can tell whether there was a premature return or not.; If the "BROKEN" function returns any other value, that
value will be interpolated into the template as if
that value had been the return value of the program
fragment to begin with. For example, if the "BROKEN"
function returns an error string, the error string
will be interpolated into the output of the template
in place of the program fragment that cased the error.; If you don't specify a "BROKEN" function, "Text::Tem
plate" supplies a default one that returns something
like

Program fragment delivered error ``Illegal di

vision by 0 at
template line 37''
(Note that the format of this message has changed slightly since version 1.31.) The return value of the "BROKEN" function is interpolated into the template at the place the error occurred, so that this template:: (3+4)*5 = { 3+4)*5 }
yields this result:: (3+4)*5 = Program fragment delivered error; ``syntax error at template line 1''
If you specify a value for the "BROKEN" attribute, it should be a reference to a function that "fill_in" can call instead of the default function.
"fill_in" will pass a hash to the "broken" function. The hash will have at least these three members:
"text": The source code of the program fragment that
failed
"error": The text of the error message ($@) generated by
eval.; The text has been modified to omit the trailing
newline and to include the name of the template
file (if there was one). The line number counts
from the beginning of the template, not from the
beginning of the failed program fragment.
"lineno": The line number of the template at which the pro
gram fragment began.
There may also be an "arg" member. See "BROKEN_ARG", below
"BROKEN_ARG": If you supply the "BROKEN_ARG" option to "fill_in",
the value of the option is passed to the "BROKEN"
function whenever it is called. The default "BROKEN"
function ignores the "BROKEN_ARG", but you can write a
custom "BROKEN" function that uses the "BROKEN_ARG" to
get more information about what went wrong.; The "BROKEN" function could also use the "BROKEN_ARG"
as a reference to store an error message or some other
information that it wants to communicate back to the
caller. For example:

$error = '';

sub my_broken {
my %args = @_;
my $err_ref = $args{arg};
...
$$err_ref = "Some error message";
return undef;

}

$template->fill_in(BROKEN => my_broken,

BROKEN_ARG => rror,

);
if ($error) {: die "It didn't work: $error";
}
If one of the program fragments in the template fails, it will call the "BROKEN" function, "my_broken", and pass it the "BROKEN_ARG", which is a reference to $error. "my_broken" can store an error message into $error this way. Then the function that called "fill_in" can see if "my_broken" has left an error message for it to find, and proceed accordingly.
"SAFE": If you give "fill_in" a "SAFE" option, its value
should be a safe compartment object from the "Safe"
package. All evaluation of program fragments will be
performed in this compartment. See Safe for full
details about such compartments and how to restrict
the operations that can be performed in them.; If you use the "PACKAGE" option with "SAFE", the pack
age you specify will be placed into the safe compart
ment and evaluation will take place in that package as
usual.; If not, "SAFE" operation is a little different from
the default. Usually, if you don't specify a package,
evaluation of program fragments occurs in the package
from which the template was invoked. But in "SAFE"
mode the evaluation occurs inside the safe compartment
and cannot affect the calling package. Normally, if
you use "HASH" without "PACKAGE", the hash variables
are imported into a private, one-use-only package.
But if you use "HASH" and "SAFE" together without
"PACKAGE", the hash variables will just be loaded into
the root namespace of the "Safe" compartment.
"OUTPUT": If your template is going to generate a lot of text
that you are just going to print out again anyway,
you can save memory by having "Text::Template" print
out the text as it is generated instead of making it
into a big string and returning the string. If you
supply the "OUTPUT" option to "fill_in", the value
should be a filehandle. The generated text will be
printed to this filehandle as it is constructed. For
example:

$template->fill_in(OUTPUT => TDOUT, ...);
fills in the $template as usual, but the results are immediately printed to STDOUT. This may result in the output appearing more quickly than it would have oth erwise.
If you use "OUTPUT", the return value from "fill_in" is still true on success and false on failure, but the complete text is not returned to the caller.
"PREPEND": You can have some Perl code prepended automatically to
the beginning of every program fragment. See
""PREPEND" feature and using "strict" in templates"
below.
"DELIMITERS": If this option is present, its value should be a ref
erence to a list of two strings. The first string is
the string that signals the beginning of each program
fragment, and the second string is the string that
signals the end of each program fragment. See "Alter
native Delimiters", below.; If you specify "DELIMITERS" in the call to "fill_in",
they override any delimiters you set when you created
the template object with "new".

Convenience Functions

"fill_this_in"

The basic way to fill in a template is to create a tem
plate object and then call "fill_in" on it. This is use
ful if you want to fill in the same template more than
once.

In some programs, this can be cumbersome. "fill_this_in"
accepts a string, which contains the template, and a list
of options, which are passed to "fill_in" as above. It
constructs the template object for you, fills it in as
specified, and returns the results. It returns "undef"
and sets $Text::Template::ERROR if it couldn't generate
any results.

An example:: $Q::name = 'Donald';
$Q::amount = 141.61;
$Q::part = 'hyoid bone';; $text = Text::Template->fill_this_in( <<'EOM',; PACKAGE => Q);
Dear {$name},
You owe me sprintf('%.2f', $amount)}.
Pay or I will break your {$part}.
Love,
Grand Vizopteryx of Irkutsk.; EOM
Notice how we included the template in-line in the program by using a `here document' with the "<<" notation.
"fill_this_in" is a deprecated feature. It is only here for backwards compatibility, and may be removed in some far-future version in "Text::Template". You should use "fill_in_string" instead. It is described in the next section.
"fill_in_string"
It is stupid that "fill_this_in" is a class method. It should have been just an imported function, so that you could omit the "Text::Template->" in the example above. But I made the mistake four years ago and it is too late to change it.
"fill_in_string" is exactly like "fill_this_in" except that it is not a method and you can omit the "Text::Tem plate->" and just say: print fill_in_string(<<'EOM', ...);
Dear {$name},
...; EOM
To use "fill_in_string", you need to say: use Text::Template 'fill_in_string';
at the top of your program. You should probably use "fill_in_string" instead of "fill_this_in".
"fill_in_file"
If you import "fill_in_file", you can say: $text = fill_in_file(filename, ...);
The "..." are passed to "fill_in" as above. The filename is the name of the file that contains the template you want to fill in. It returns the result text. or "undef", as usual.
If you are going to fill in the same file more than once in the same program you should use the longer "new" / "fill_in" sequence instead. It will be a lot faster because it only has to read and parse the file once.
Including files into templates
People always ask for this. ``Why don't you have an include function?'' they want to know. The short answer is this is Perl, and Perl already has an include function. If you want it, you can just put: {qx{cat filename}}
into your template. VoilA.
If you don't want to use "cat", you can write a little four-line function that opens a file and dumps out its contents, and call it from the template. I wrote one for you. In the template, you can say: {Text::Template::_load_text(filename)}
If that is too verbose, here is a trick. Suppose the tem plate package that you are going to be mentioning in the "fill_in" call is package "Q". Then in the main program, write: *Q::include = Text::Template::_load_text;
This imports the "_load_text" function into package "Q" with the name "include". From then on, any template that you fill in with package "Q" can say: {include(filename)}
to insert the text from the named file at that point. If you are using the "HASH" option instead, just put "include => Text::Template::_load_text" into the hash instead of importing it explicitly.
Suppose you don't want to insert a plain text file, but rather you want to include one template within another? Just use "fill_in_file" in the template itself:: {Text::Template::fill_in_file(filename)}
You can do the same importing trick if this is too much to type.

Miscellaneous

"my" variables

People are frequently surprised when this doesn't work:: my $recipient = 'The King';
my $text = fill_in_file('formletter.tmpl');
The text "The King" doesn't get into the form letter. Why not? Because $recipient is a "my" variable, and the whole point of "my" variables is that they're private and inac cessible except in the scope in which they're declared. The template is not part of that scope, so the template can't see $recipient.
If that's not the behavior you want, don't use "my". "my" means a private variable, and in this case you don't want the variable to be private. Put the variables into pack age variables in some other package, and use the "PACKAGE" option to "fill_in":: $Q::recipient = $recipient;
my $text = fill_in_file('formletter.tmpl', PACKAGE; => 'Q');
or pass the names and values in a hash with the "HASH" option:: my $text = fill_in_file('formletter.tmpl', HASH =>; { recipient => $recipient });
Security Matters
All variables are evaluated in the package you specify with the "PACKAGE" option of "fill_in". if you use this option, and if your templates don't do anything egre giously stupid, you won't have to worry that evaluation of the little programs will creep out into the rest of your program and wreck something.
Nevertheless, there's really no way (except with "Safe") to protect against a template that says: { $Important::Secret::Security::Enable = 0;
# Disable security checks in this program; }
or: { $/ = "ho ho ho"; # Sabotage future uses of; <FH>.
# $/ is always a global variable; }
or even: { system("rm -rf /") }
so don't go filling in templates unless you're sure you
know what's in them. If you're worried, or you can't
trust the person who wrote the template, use the "SAFE"
option.
A final warning: program fragments run a small risk of accidentally clobbering local variables in the "fill_in" function itself. These variables all have names that begin with $fi_, so if you stay away from those names you'll be safe. (Of course, if you're a real wizard you can tamper with them deliberately for exciting effects; this is actually how $OUT works.) I can fix this, but it will make the package slower to do it, so I would prefer not to. If you are worried about this, send me mail and I will show you what to do about it.
Alternative Delimiters
Lorenzo Valdettaro pointed out that if you are using "Text::Template" to generate TeX output, the choice of braces as the program fragment delimiters makes you suffer suffer suffer. Starting in version 1.20, you can change the choice of delimiters to something other than curly braces.
In either the "new()" call or the "fill_in()" call, you can specify an alternative set of delimiters with the "DELIMITERS" option. For example, if you would like code fragments to be delimited by "[@--" and "--@]" instead of "{" and "}", use: ... DELIMITERS => [ '[@--', '--@]' ], ...
Note that these delimiters are literal strings, not regexes. (I tried for regexes, but it complicates the lexical analysis too much.) Note also that "DELIMITERS" disables the special meaning of the backslash, so if you want to include the delimiters in the literal text of your template file, you are out of luck---it is up to you to choose delimiters that do not conflict with what you are doing. The delimiter strings may still appear inside of program fragments as long as they nest properly. This means that if for some reason you absolutely must have a program fragment that mentions one of the delimiters, like this:: [@-
print "Oh no, a delimiter: --@]0; --@]
you may be able to make it work by doing this instead:: [@-
# Fake matching delimiter in a comment:

[@-print "Oh no, a delimiter: --@]0; --@]
It may be safer to choose delimiters that begin with a newline character.
Because the parsing of templates is simplified by the absence of backslash escapes, using alternative "DELIM ITERS" speeds up the parsing process by 20-25%. This shows that my original choice of "{" and "}" was very bad. I therefore recommend that you use alternative delimiters whenever possible.
"PREPEND" feature and using "strict" in templates
Suppose you would like to use "strict" in your templates to detect undeclared variables and the like. But each code fragment is a separate lexical scope, so you have to turn on "strict" at the top of each and every code frag ment:: { use strict;
use vars '$foo';
$foo = 14;
...; }; ...; { # we forgot to put `use strict' here
my $result = $boo + 12; # $boo is misspelled

and should be $foo
# No error is raised on `$boo'; }
Because we didn't put "use strict" at the top of the sec ond fragment, it was only active in the first fragment, and we didn't get any "strict" checking in the second fragment. Then we mispelled $foo and the error wasn't caught.
"Text::Template" version 1.22 and higher has a new feature to make this easier. You can specify that any text at all be automatically added to the beginning of each program fragment.
When you make a call to "fill_in", you can specify a: PREPEND => 'some perl statements here'
option; the statements will be prepended to each program fragment for that one call only. Suppose that the "fill_in" call included a: PREPEND => 'use strict;'
option, and that the template looked like this:: { use vars '$foo';
$foo = 14;
...; }; ...; { my $result = $boo + 12; # $boo is misspelled; and should be $foo
...; }
The code in the second fragment would fail, because $boo has not been declared. "use strict" was implied, even though you did not write it explicitly, because the "PREPEND" option added it for you automatically.
There are two other ways to do this. At the time you cre ate the template object with "new", you can also supply a "PREPEND" option, in which case the statements will be prepended each time you fill in that template. If the "fill_in" call has its own "PREPEND" option, this over rides the one specified at the time you created the tem plate. Finally, you can make the class method call: Text::Template->always_prepend('perl statements');
If you do this, then call calls to "fill_in" for any tem plate will attach the perl statements to the beginning of each program fragment, except where overridden by "PREPEND" options to "new" or "fill_in".
Prepending in Derived Classes
This section is technical, and you should skip it on the first few readings.
Normally there are three places that prepended text could come from. It could come from the "PREPEND" option in the "fill_in" call, from the "PREPEND" option in the "new" call that created the template object, or from the argu ment of the "always_prepend" call. "Text::Template" looks for these three things in order and takes the first one that it finds.
In a subclass of "Text::Template", this last possibility is ambiguous. Suppose "S" is a subclass of "Text::Tem plate". Should: Text::Template->always_prepend(...);
affect objects in class "Derived"? The answer is that you can have it either way.
The "always_prepend" value for "Text::Template" is nor mally stored in a hash variable named %GLOBAL_PREPEND under the key "Text::Template". When "Text::Template" looks to see what text to prepend, it first looks in the template object itself, and if not, it looks in $GLOBAL_PREPEND{class} where class is the class to which the template object belongs. If it doesn't find any value, it looks in $GLOBAL_PREPEND{'Text::Template'}. This means that objects in class "Derived" will be affected by: Text::Template->always_prepend(...);
unless there is also a call to: Derived->always_prepend(...);
So when you're designing your derived class, you can arrange to have your objects ignore "Text::Tem plate::always_prepend" calls by simply putting "Derived->always_prepend('')" at the top of your module.
Of course, there is also a final escape hatch: Templates support a "prepend_text" that is used to look up the appropriate text to be prepended at "fill_in" time. Your derived class can override this method to get an arbitrary effect.
JavaScript
Jennifer D. St Clair asks:: > Most of my pages contain JavaScript and; Stylesheets.
> How do I change the template identifier?
Jennifer is worried about the braces in the JavaScript being taken as the delimiters of the Perl program frag ments. Of course, disaster will ensue when perl tries to evaluate these as if they were Perl programs. The best choice is to find some unambiguous delimiter strings that you can use in your template instead of curly braces, and then use the "DELIMITERS" option. However, if you can't do this for some reason, there are two easy workarounds:
1. You can put " its special meaning. So, for example, instead of: if (br== "n3") {
// etc.
}
you can put: if (br== "n3")
// etc.
and it'll come out of the template engine the way you want.
But here is another method that is probably better. To see how it works, first consider what happens if you put this into a template:: { 'foo' }
Since it's in braces, it gets evaluated, and obviously, this is going to turn into: foo
So now here's the trick: In Perl, "q{...}" is the same as '...'. So if we wrote: {q{foo}}
it would turn into: foo
So for your JavaScript, just write: {q{if (br== "n3") {
// etc.
}}
}
and it'll come out as: if (br== "n3") {
// etc.
}
which is what you want.
Shut Up!
People sometimes try to put an initialization section at the top of their templates, like this:: { ...
$var = 17;
}
Then they complain because there is a 17 at the top of the output that they didn't want to have there.
Remember that a program fragment is replaced with its own return value, and that in Perl the return value of a code block is the value of the last expression that was evalu ated, which in this case is 17. If it didn't do that, you wouldn't be able to write "{$recipient}" and have the recipient filled in.
To prevent the 17 from appearing in the output is very simple:: { ...
$var = 17;
'';
}
Now the last expression evaluated yields the empty string, which is invisible. If you don't like the way this looks, use: { ...
$var = 17;
($SILENTLY);
}
instead. Presumably, $SILENTLY has no value, so nothing will be interpolated. This is what is known as a `trick'.
Compatibility
Every effort has been made to make this module compatible with older versions. The only known exceptions follow:
The output format of the default "BROKEN" subroutine has changed twice, most recently between versions 1.31 and 1.40.
Starting in version 1.10, the $OUT variable is arrogated for a special meaning. If you had templates before ver sion 1.10 that happened to use a variable named $OUT, you will have to change them to use some other variable or all sorts of strangeness will result.
Between versions 0.1b and 1.00 the behavior of the
metacharacter changed. In 0.1b, was special every where, and the template processor always replaced it with a single backslash before passing the code to Perl for evaluation. The rule now is more complicated but probably more convenient. See the section on backslash processing, below, for a full discussion.
Backslash Processing
In "Text::Template" beta versions, the backslash was spe cial whenever it appeared before a brace or another back slash. That meant that while "{"0}" did indeed generate a newline, "{" the code passed to Perl for evaluation was " syntax error. If you wanted a backslash, you would have had to write "{"
In "Text::Template" versions 1.00 through 1.10, there was a bug: Backslash was special everywhere. In these ver sions, "{"0}" generated the letter "n".
The bug has been corrected in version 1.11, but I did not go back to exactly the old rule, because I did not like the idea of having to write "{" slash. The rule is now more complicated to remember, but probably easier to use. The rule is now: Backslashes are always passed to Perl unchanged unless they occur as part of a sequence like " texts, they are special; " "" and "" signal a literal brace.
Examples:: foo
is not evaluated, because the " nals that they should be taken literally. The result in the output looks like this:: { foo }
This is a syntax error:: { "foo}" }
because "Text::Template" thinks that the code ends at the first "}", and then gets upset when it sees the second one. To make this work correctly, use: { "foo" }
This passes "foo}" to Perl for evaluation. Note there's no " the evaluated code, use: { "foo
This passes "foo" to Perl for evaluation.
Starting with "Text::Template" version 1.20, backslash processing is disabled if you use the "DELIMITERS" option to specify alternative delimiter strings.
A short note about $Text::Template::ERROR
In the past some people have fretted about `violating the package boundary' by examining a variable inside the "Text::Template" package. Don't feel this way. $Text::Template::ERROR is part of the published, official interface to this package. It is perfectly OK to inspect this variable. The interface is not going to change.
If it really, really bothers you, you can import a func tion called "TTerror" that returns the current value of the $ERROR variable. So you can say:: use Text::Template 'TTerror';; my $template = new Text::Template (SOURCE =>
$filename); unless ($template) { my $err = TTerror; die "Couldn't make template: $err; aborting";
}
I don't see what benefit this has over just doing this:: use Text::Template;; my $template = new Text::Template (SOURCE =>
$filename)or die "Couldn't make template: $Text::Tem
plate::ERROR; aborting";
But if it makes you happy to do it that way, go ahead.
Sticky Widgets in Template Files
The "CGI" module provides functions for `sticky widgets', which are form input controls that retain their values from one page to the next. Sometimes people want to know how to include these widgets into their template output.
It's totally straightforward. Just call the "CGI" func tions from inside the template:: { $q->checkbox_group(NAME => 'toppings',
LINEBREAK => true,
COLUMNS => 3,
VALUES => @toppings,
);
}
Automatic preprocessing of program fragments
It may be useful to preprocess the program fragments before they are evaluated. See "Text::Template::Prepro cess" for more details.
Author
Mark-Jason Dominus, Plover Systems
Please send questions and other remarks about this software to "mjd-perl-template+@plover.com"
You can join a very low-volume (<10 messages per year) mailing list for announcements about this package. Send an empty note to "mjd-perl-template-request@plover.com" to join.
For updates, visit "http://www.plover.com/~mjd/perl/Tem plate/".
Support?
This software is version 1.43. It may have bugs. Sugges tions and bug reports are always welcome. Send them to "mjd-perl-template+@plover.com". (That is my address, not the address of the mailing list. The mailing list address is a secret.)

LICENSE

This program 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 ver
sion 2 of the License, or (at your option) any later version. You
may also can redistribute it and/or modify it under the terms of
the Perl Artistic License.
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 copies of the GNU General
Public License along with this program; if not, write to the Free
Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
MA 02111-1307, USA.

THANKS

Many thanks to the following people for offering support,
encouragement, advice, bug reports, and all the other good
stuff.

David H. Adler / Joel Appelbaum / Klaus Arnhold / Kevin
Atteson / Chris.Brezil / Mike Brodhead / Tom Brown / Tim
Bunce / Juan E. Camacho / Itamar Almeida de Carvalho /
Joseph Cheek / Gene Damon / San Deng / Bob Dougherty /
Marek Grac / Dan Franklin / gary at dls.net / Todd A.
Green / Donald L. Greer Jr. / Michelangelo Grigni / Tom
Henry / Matt X. Hunter / Robert M. Ioffe / Daniel LaLib
erte / Reuven M. Lerner / Trip Lilley / Yannis Livassof /
David Marshall / Joel Meulenberg / Jason Moore / Chris
Nandor / Bek Oberin / Steve Palincsar / Ron Pero / Hans
Persson / Jonathan Roy / Shabbir J. Safdar / Jennifer D.
St Clair / Uwe Schneider / Randal L. Schwartz / Michael G
Schwern / Brian C. Shensky / Niklas Skoglund / Tom Snee /
Hans Stoop / Michael J. Suzio / Dennis Taylor / James H.
Thompson / Shad Todd / Lorenzo Valdettaro / Larry Virden /
Andy Wardley / Archie Warnock / Matt Womer / Andrew G Wood
/ Daini Xie / Michaely Yeung

Special thanks to:

Jonathan Roy: for telling me how to do the "Safe" support (I spent two
years worrying about it, and then Jonathan pointed out
that it was trivial.); Ranjit Bhatnagar
for demanding less verbose fragments like they have in
ASP, for helping me figure out the Right Thing, and,
especially, for talking me out of adding any new syntax.
These discussions resulted in the $OUT feature.; Bugs and Caveats; "my" variables in "fill_in" are still susceptible to being
clobbered by template evaluation. They all begin with
"fi_", so avoid those names in your templates.; The line number information will be wrong if the tem
plate's lines are not terminated by "0. You should let
me know if this is a problem. If you do, I will fix it.; The $OUT variable has a special meaning in templates, so
you cannot use it as if it were a regular variable.; There are not quite enough tests in the test suite.

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