NAME
Text::Template - Expand template text with embedded Perl
VERSION
version 1.61
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 => 'Saruman',
fearsome => 'Sauron' },
};
$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';});
DESCRIPTION
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.
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 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. Smith,
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 => 'John',
lastname => 'Smith',
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" }
Philosophy
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.
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 \
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 evaluated 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.
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{ * $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.
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 directory
new
$template = Text::Template->new( 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:
Text::Template->new( 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:
Text::Template->new( 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:
Text::Template->new( 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:
Text::Template->new ( 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
-
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 "Alternative Delimiters", below. ENCODING
-
You may also add a
ENCODING
option. If this option is present, and theSOURCE
is aFILE
, then the data will be decoded from the given encoding using the Encode module. You can use any encoding that Encode recognizes. E.g.:Text::Template->new( TYPE => 'FILE', ENCODING => 'UTF-8', SOURCE => 'xyz.tmpl');
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 supplyingUNTAINT => 1
in the call tonew
. This will tellText::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 withTYPE => 'string'
orTYPE => '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
-
This option is passed along to the
fill_in
call unless it is overridden in the arguments tofill_in
. SeePREPEND
feature and usingstrict
in templates> below. BROKEN
-
This option is passed along to the
fill_in
call unless it is overridden in the arguments tofill_in
. SeeBROKEN
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 $Text::Template::ERROR
.
The OPTIONS are a hash, or a list of key-value pairs. You can write the key names in any of the six usual styles as above; this means that where this manual says PACKAGE
(for example) you can actually use any of
PACKAGE Package package -PACKAGE -Package -package
Pick a style you like and stick with it. The all-lowercase versions may yield spurious warnings about
Ambiguous use of package => resolved to "package"
so you might like to avoid them and use the capitalized versions.
At present, there are eight legal options: PACKAGE
, BROKEN
, BROKEN_ARG
, FILENAME
, SAFE
, HASH
, OUTPUT
, and DELIMITERS
.
PACKAGE
-
PACKAGE
specifies the name of a package in which the program fragments should be evaluated. The default is to use the package from whichfill_in
was called. For example, consider this template:The value of the variable x is {$x}.
If you use
$template->fill_in(PACKAGE => 'R')
, then the$x
in the template is actually replaced with the value of$R::x
. If you omit thePACKAGE
option,$x
will be replaced with the value of the$x
variable in the package that actually calledfill_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
$item_no
in scope in your program at the point you calledfill_in
, its value would be clobbered by the act of filling out the template. The problem is the same as if you had written a subroutine that used those variables in the same way that the template does. ($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 withmy
. 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 withmy
:@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'], object => \$self, } );
will fill out the template and use
"The King"
as the value of$recipient
and the list of items as the value of@items
. Note that we pass an array reference, but inside the template it appears as an array. In general, anything other than a simple string or number should be passed by reference.We also want to pass an object, which is in
$self
; note that we pass a reference to the object,\$self
instead. Since we've passed a reference to a scalar, inside the template the object appears as$object
.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.
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.For anything else, you must pass a reference.
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 thatvar => "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.)
In particular, if you want the template to get an object or any kind, you must pass a reference to it:
$template->fill_in(HASH => { database_handle => \$dbh, ... });
If you do this, the template will have a variable
$database_handle
which is the database handle object. If you leave out the\
, the template will have a hash%database_handle
, which exposes the internal structure of the database handle object; you don't want that.
Normally, the way this works is by allocating a private package, loading all the variables into the package, and then filling out the template as if you had specified that package. A new package is allocated each time. However, if you also use the
PACKAGE
option,Text::Template
loads the variables into the package you specified, and they stay there after the call returns. Subsequent calls tofill_in
that use the same package will pick up the values you loaded in.If the argument of
HASH
is a reference to an array instead of a reference to a hash, then the array should contain a list of hashes whose contents are loaded into the template package one after the other. You can use this feature if you want to combine several sets of variables. For example, one set of variables might be the defaults for a fill-in form, and the second set might be the user inputs, which override the defaults when they are present:$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 theBROKEN
function. TheBROKEN
function will tellText::Template
what to do next.If the
BROKEN
function returnsundef
,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 afterfill_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 theBROKEN
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 likeProgram 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 thatfill_in
can call instead of the default function.fill_in
will pass a hash to thebroken
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 (
$@
) generated by eval.The text has been modified to omit the trailing newline and to include the name of the template file (if there was one). The line number counts from the beginning of the template, not from the beginning of the failed program fragment.
lineno
-
The line number of the template at which the program fragment began.
There may also be an
arg
member. SeeBROKEN_ARG
, below BROKEN_ARG
-
If you supply the
BROKEN_ARG
option tofill_in
, the value of the option is passed to theBROKEN
function whenever it is called. The defaultBROKEN
function ignores theBROKEN_ARG
, but you can write a customBROKEN
function that uses theBROKEN_ARG
to get more information about what went wrong.The
BROKEN
function could also use theBROKEN_ARG
as a reference to store an error message or some other information that it wants to communicate back to the caller. For example:$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: $error"; }
If one of the program fragments in the template fails, it will call the
BROKEN
function,my_broken
, and pass it theBROKEN_ARG
, which is a reference to$error
.my_broken
can store an error message into$error
this way. Then the function that calledfill_in
can see ifmy_broken
has left an error message for it to find, and proceed accordingly. FILENAME
-
If you give
fill_in
aFILENAME
option, then this is the file name that you loaded the template source from. This only affects the error message that is given for template errors. If you loaded the template fromfoo.txt
for example, and passfoo.txt
as theFILENAME
parameter, errors will look like... at foo.txt line N
rather than... at template line N
.Note that this does NOT have anything to do with loading a template from the given filename. See
fill_in_file()
for that.For example:
my $template = Text::Template->new( TYPE => 'string', SOURCE => 'The value is {1/0}'); $template->fill_in(FILENAME => 'foo.txt') or die $Text::Template::ERROR;
will die with an error that contains
Illegal division by zero at at foo.txt line 1
SAFE
-
If you give
fill_in
aSAFE
option, its value should be a safe compartment object from theSafe
package. All evaluation of program fragments will be performed in this compartment. See Safe for full details about such compartments and how to restrict the operations that can be performed in them.If you use the
PACKAGE
option withSAFE
, the package you specify will be placed into the safe compartment and evaluation will take place in that package as usual.If not,
SAFE
operation is a little different from the default. Usually, if you don't specify a package, evaluation of program fragments occurs in the package from which the template was invoked. But inSAFE
mode the evaluation occurs inside the safe compartment and cannot affect the calling package. Normally, if you useHASH
withoutPACKAGE
, the hash variables are imported into a private, one-use-only package. But if you useHASH
andSAFE
together withoutPACKAGE
, the hash variables will just be loaded into the root namespace of theSafe
compartment. OUTPUT
-
If your template is going to generate a lot of text that you are just going to print out again anyway, you can save memory by having
Text::Template
print out the text as it is generated instead of making it into a big string and returning the string. If you supply theOUTPUT
option tofill_in
, the value should be a filehandle. The generated text will be printed to this filehandle as it is constructed. For example:$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 fromfill_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 usingstrict
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 tofill_in
, they override any delimiters you set when you created the template object withnew
.
Convenience Functions
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.
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. 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.
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 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 });
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 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.
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: --@]\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
may speed up the parsing process by 20-25%. This shows that my original choice of {
and }
was very bad.
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 misspelled $foo
and the error wasn't caught.
Text::Template
version 1.22 and higher has a new feature to make this easier. You can specify that any text at all be automatically added to the beginning of each program fragment.
When you make a call to fill_in
, you can specify a
PREPEND => 'some perl statements here'
option; the statements will be prepended to each program fragment for that one call only. Suppose that the fill_in
call included a
PREPEND => 'use strict;'
option, and that the template looked like this:
{ use vars '$foo';
$foo = 14;
...
}
...
{ my $result = $boo + 12; # $boo is misspelled and should be $foo
...
}
The code in the second fragment would fail, because $boo
has not been declared. use strict
was implied, even though you did not write it explicitly, because the PREPEND
option added it for you automatically.
There are three other ways to do this. At the time you create the template object with new
, you can also supply a PREPEND
option, in which case the statements will be prepended each time you fill in that template. If the fill_in
call has its own PREPEND
option, this overrides the one specified at the time you created the template. Finally, you can make the class method call
Text::Template->always_prepend('perl statements');
If you do this, then call calls to fill_in
for any template will attach the perl statements to the beginning of each program fragment, except where overridden by PREPEND
options to new
or fill_in
.
An alternative to adding "use strict;" to the PREPEND option, you can pass STRICT => 1 to fill_in when also passing the HASH option.
Suppose that the fill_in
call included both
HASH => {$foo => ''} and
STRICT => 1
options, and that the template looked like this:
{
$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 STRICT
option added it for you automatically. Any variable referenced in the template that is not in the HASH
option will be an error.
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 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.
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 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.
head2 Shut Up!
People sometimes try to put an initialization section at the top of their templates, like this:
{ ...
$var = 17;
}
Then they complain because there is a 17
at the top of the output that they didn't want to have there.
Remember that a program fragment is replaced with its own return value, and that in Perl the return value of a code block is the value of the last expression that was evaluated, which in this case is 17. If it didn't do that, you wouldn't be able to write {$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'.
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 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.
Backslash Processing
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.
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 function called TTerror
that returns the current value of the $ERROR
variable. So you can say:
use Text::Template 'TTerror';
my $template = Text::Template->new(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 = Text::Template->new(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.
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
functions 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::Preprocess
for more details.
Automatic postprocessing of template hunks
It may be useful to process hunks of output before they are appended to the result text. For this, subclass and replace the append_text_to_result
method. It is passed a list of pairs with these entries:
handle - a filehandle to which to print the desired output
out - a ref to a string to which to append, to use if handle is not given
text - the text that will be appended
type - where the text came from: TEXT for literal text, PROG for code
HISTORY
Originally written by Mark Jason Dominus, Plover Systems (versions 0.01 - 1.46)
Maintainership transferred to Michael Schout <mschout@cpan.org> in version 1.47
THANKS
Many thanks to the following people for offering support, encouragement, advice, bug reports, and all the other good stuff.
Andrew G Wood
Andy Wardley
António Aragão
Archie Warnock
Bek Oberin
Bob Dougherty
Brian C. Shensky
Chris Nandor
Chris Wesley
Chris.Brezil
Daini Xie
Dan Franklin
Daniel LaLiberte
David H. Adler
David Marshall
Dennis Taylor
Donald L. Greer Jr.
Dr. Frank Bucolo
Fred Steinberg
Gene Damon
Hans Persson
Hans Stoop
Itamar Almeida de Carvalho
James H. Thompson
James Mastros
Jarko Hietaniemi
Jason Moore
Jennifer D. St Clair
Joel Appelbaum
Joel Meulenberg
Jonathan Roy
Joseph Cheek
Juan E. Camacho
Kevin Atteson
Kevin Madsen
Klaus Arnhold
Larry Virden
Lieven Tomme
Lorenzo Valdettaro
Marek Grac
Matt Womer
Matt X. Hunter
Michael G Schwern
Michael J. Suzio
Michaely Yeung
Michelangelo Grigni
Mike Brodhead
Niklas Skoglund
Randal L. Schwartz
Reuven M. Lerner
Robert M. Ioffe
Ron Pero
San Deng
Sean Roehnelt
Sergey Myasnikov
Shabbir J. Safdar
Shad Todd
Steve Palincsar
Tim Bunce
Todd A. Green
Tom Brown
Tom Henry
Tom Snee
Trip Lilley
Uwe Schneider
Val Luck
Yannis Livassof
Yonat Sharon
Zac Hansen
gary at dls.net
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 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.
SOURCE
The development version is on github at https://https://github.com/mschout/perl-text-template and may be cloned from git://https://github.com/mschout/perl-text-template.git
BUGS
Please report any bugs or feature requests on the bugtracker website https://github.com/mschout/perl-text-template/issues
When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.
AUTHOR
Michael Schout <mschout@cpan.org>
COPYRIGHT AND LICENSE
This software is copyright (c) 2013 by Mark Jason Dominus <mjd@cpan.org>.
This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.