my variables
PREPEND feature and using strict in templates
$Text::Template::ERROR
Text::Template - Expand template text with embedded Perl
This file documents Text::Template version 1.42
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 => \*FILEHANDLE, ...);
# 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';});
This is a library for generating form letters, building HTML pages, or filling in templates generally. A `template' is a piece of text that has little Perl programs embedded in it here and there. When you `fill in' a template, 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 program. 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 encourages functional separation.
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 delinquent 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 delinquent 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::Template::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::Template::ERROR" }
When people make a template module like this one, they almost always
start by inventing a special syntax for substitutions. 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 language 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 beginning and } at the end.
If you want a variable interpolated, you write it the way you would in
Perl. If you need to make a loop, you can use any of the Perl loop
constructions. All the Perl built-in functions are available.
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 \ in front of a brace (or another 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 problem 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.\n" }
The backslash inside the string is passed through to Perl unchanged,
so the \n really does turn into a newline. See the note at the end
for details about the way backslashes 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 statements, 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 output 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.
$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{ * $i\n};
}
$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 .= " * $i\n";
}
}
$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.
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 directory
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 reference 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 => \*STDIN );
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
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 "Alternative 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 person might have tampered with the file.)
In some environments, however, local files are trustworthy. 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 considered
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 tainting.
Thanks to Steve Palincsar, Gerard Vreeswijk, and Dr. Christoph Baehr for help with this feature.
PREPEND
fill_in call unless it is
overridden in the arguments to fill_in. See PREPEND feature
and using strict in templates below.
BROKEN
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; otherwise 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 successful.
Otherwise, returns undef and sets $Text::Template::ERROR.
The OPTIONS are a hash, or a list of key-value pairs. You can
write the key names in any of the six usual styles as above; this
means that where this manual says PACKAGE (for example) you can
actually use any of
PACKAGE Package package -PACKAGE -Package -package
Pick a style you like and stick with it. The all-lowercase versions may yield spurious warnings about
Ambiguous use of package => resolved to "package"
so you might like to avoid them and use the capitalized versions.
At present, there are eight legal options: PACKAGE, BROKEN,
BROKEN_ARG, SAFE, HASH, OUTPUT, and DELIMITERS.
PACKAGE
PACKAGE specifies the name of a package in which the program
fragments should be evaluated. The default is to use the package from
which fill_in was called. For example, consider this template:
The value of the variable x is {$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 `Security'.
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 .= " $item_no. \u$item\n";
}
}
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 $item_no in scope in your program at the point
you called fill_in, its value would be clobbered by the act of
filling out the template. The problem is the same as if you had
written a subroutine that used those variables in the same way that
the template does. ($OUT is special in templates 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 program was using.
Templates cannot affect variables in the main program that are
declared with my, unless you give the template 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 alternative.
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 section.
Suppose the key in the hash is key and the value is value.
undef, then any variables named $key,
@key, %key, etc., are undefined.
$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. Similarly if value is any other kind of
reference. This means that
var => "foo"
and
var => \"foo"
have almost exactly the same effect. (The difference 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 private package,
loading all the variables into the package, 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 several sets
of variables. For example, one set of variables might be the defaults
for a fill-in form, and the second set might be the user inputs, which
override the defaults when they are present:
$template->fill_in(HASH => [\%defaults, \%user_input]);
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 $v to "The King" and @v to (1,2,3).
BROKEN
If any of the program fragments fails to compile or aborts for any
reason, and you have set the BROKEN option to a function reference,
Text::Template will invoke the function. This function is called
the BROKEN function. The BROKEN function will tell
Text::Template what to do next.
If the BROKEN function returns undef, Text::Template will
immediately abort processing the template and return the text that it
has accumulated so far. If your function does this, it should set a
flag that you can examine after fill_in returns so that you can
tell whether there was a premature return or not.
If the BROKEN function returns any other value, that value will be
interpolated into the template as if that value had been the return
value of the program fragment to begin with. For example, if the
BROKEN function returns an error string, the error string will be
interpolated into the output of the template in place of the program
fragment that cased the error.
If you don't specify a BROKEN function, Text::Template supplies
a default one that returns something like
Program fragment delivered error ``Illegal division by 0 at template line 37''
(Note that the format of this message has changed slightly since
version 1.31.) The return value of the BROKEN function is
interpolated into the template at the place the error occurred, so
that this template:
(3+4)*5 = { 3+4)*5 }
yields this result:
(3+4)*5 = Program fragment delivered error ``syntax error at template line 1''
If you specify a value for the BROKEN attribute, it should be a
reference to a function that fill_in can call instead of the
default function.
fill_in will pass a hash to the broken function.
The hash will have at least these three members:
text
error
The text of the error message ($@) 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
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;
}
$template->fill_in(BROKEN => \&my_broken, BROKEN_ARG => \$error, );
if ($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 package you specify
will be placed into the safe compartment 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 => \*STDOUT, ...);
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 otherwise.
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
PREPEND feature and using
strict in templates below.
DELIMITERS
If this option is present, its value should be a reference 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 "Alternative 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.
fill_this_in
The basic way to fill in a template is to create a template object and
then call fill_in on it. This is useful 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::Template-> 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.
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. Voilà.
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 template 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.
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 inaccessible 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 package 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 });
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 egregiously 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.
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: --@]\n" --@]
you may be able to make it work by doing this instead:
[@-- # Fake matching delimiter in a comment: [@-- print "Oh no, a delimiter: --@]\n" --@]
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 DELIMITERS 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 fragment:
{ 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 second 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 create 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 overrides the one specified at the time you created the
template. 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 template will
attach the perl statements to the beginning of each program fragment,
except where overridden by PREPEND options to new or fill_in.
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 argument 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::Template. 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 normally 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::Template::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.
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 fragments. 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 \ in front of {, }, or \ to remove 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.
People sometimes try to put an initialization section at the top of their templates, like this:
{ ...
$var = 17;
}
Then they complain because there is a 17 at the top of the output
that they didn't want to have there.
Remember that a program fragment is replaced with its own return
value, and that in Perl the return value of a code block is the value
of the last expression that was evaluated, which in this case is 17.
If it didn't do that, you wouldn't be able to write {$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'.
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 version 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 everywhere, 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.
In Text::Template beta versions, the backslash was special whenever
it appeared before a brace or another backslash. That meant that
while {"\n"} did indeed generate a newline, {"\\"} did not
generate a backslash, because the code passed to Perl for evaluation
was "\" which is a 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 versions, {"\n"}
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 {"\\\\"} to get one backslash. 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 \\\\\\{ or \\\\\\}. In these
contexts, they are special; \\ is replaced with \, and \{ and
\} signal a literal brace.
Examples:
\{ foo \}
is not evaluated, because the \ before the braces signals 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 \ in
the evaluated code. If you really want a \ in 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.
$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 function 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::Template::ERROR; aborting";
But if it makes you happy to do it that way, go ahead.
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 functions from
inside the template:
{ $q->checkbox_group(NAME => 'toppings',
LINEBREAK => true,
COLUMNS => 3,
VALUES => \@toppings,
);
}
It may be useful to preprocess the program fragments before they are
evaluated. See Text::Template::Preprocess for more details.
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/Template/.
This software is version 1.42. It may have bugs. Suggestions 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.)
Text::Template version 1.42
Copyright (C) 2001 Mark Jason Dominus
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 version 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.
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 / Dan Franklin / gary at dls.net / Todd A. Green / Donald L. Greer Jr. / Michelangelo Grigni / Tom Henry / Matt X. Hunter / Robert M. Ioffe / Daniel LaLiberte / 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:
Safe support (I spent two years
worrying about it, and then Jonathan pointed out that it was trivial.)
$OUT feature.
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 template's lines are
not terminated by "\n". 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.