1Text::Template(3) User Contributed Perl Documentation Text::Template(3)
2
6 Text::Template - Expand template text with embedded Perl
7
9 version 1.61
10
12 use Text::Template;
13 $template = Text::Template->new(TYPE => 'FILE', SOURCE => 'filename.tmpl');
16 $template = Text::Template->new(TYPE => 'ARRAY', SOURCE => [ ... ] );
17 $template = Text::Template->new(TYPE => 'FILEHANDLE', SOURCE => $fh );
18 $template = Text::Template->new(TYPE => 'STRING', SOURCE => '...' );
19 $template = Text::Template->new(PREPEND => q{use strict;}, ...);
20 # Use a different template file syntax:
22 $template = Text::Template->new(DELIMITERS => [$open, $close], ...);
23 $recipient = 'King';
25 $text = $template->fill_in(); # Replaces `{$recipient}' with `King'
26 print $text;
27 $T::recipient = 'Josh';
29 $text = $template->fill_in(PACKAGE => T);
30 # Pass many variables explicitly
32 $hash = { recipient => 'Abed-Nego',
33 friends => [ 'me', 'you' ],
34 enemies => { loathsome => 'Saruman',
35 fearsome => 'Sauron' },
36 };
37 $text = $template->fill_in(HASH => $hash, ...);
38 # $recipient is Abed-Nego,
39 # @friends is ( 'me', 'you' ),
40 # %enemies is ( loathsome => ..., fearsome => ... )
41 # Call &callback in case of programming errors in template
44 $text = $template->fill_in(BROKEN => \&callback, BROKEN_ARG => $ref, ...);
45 # Evaluate program fragments in Safe compartment with restricted permissions
47 $text = $template->fill_in(SAFE => $compartment, ...);
48 # Print result text instead of returning it
50 $success = $template->fill_in(OUTPUT => \*FILEHANDLE, ...);
51 # Parse template with different template file syntax:
53 $text = $template->fill_in(DELIMITERS => [$open, $close], ...);
54 # Note that this is *faster* than using the default delimiters
55 # Prepend specified perl code to each fragment before evaluating:
57 $text = $template->fill_in(PREPEND => q{use strict 'vars';}, ...);
58 use Text::Template 'fill_in_string';
60 $text = fill_in_string( <<'EOM', PACKAGE => 'T', ...);
61 Dear {$recipient},
62 Pay me at once.
63 Love,
64 G.V.
65 EOM
66 use Text::Template 'fill_in_file';
68 $text = fill_in_file($filename, ...);
69 # All templates will always have `use strict vars' attached to all fragments
71 Text::Template->always_prepend(q{use strict 'vars';});
72
74 This is a library for generating form letters, building HTML pages, or
75 filling in templates generally. A `template' is a piece of text that
76 has little Perl programs embedded in it here and there. When you `fill
77 in' a template, you evaluate the little programs and replace them with
78 their values.
79 You can store a template in a file outside your program. People can
81 modify the template without modifying the program. You can separate
82 the formatting details from the main code, and put the formatting parts
83 of the program into the template. That prevents code bloat and
84 encourages functional separation.
85 Example
87 Here's an example of a template, which we'll suppose is stored in the
88 file "formletter.tmpl":
89 Dear {$title} {$lastname},
91 It has come to our attention that you are delinquent in your
93 {$monthname[$last_paid_month]} payment. Please remit
94 ${sprintf("%.2f", $amount)} immediately, or your patellae may
95 be needlessly endangered.
96 Love,
98 Mark "Vizopteryx" Dominus
100 The result of filling in this template is a string, which might look
102 something like this:
103 Dear Mr. Smith,
105 It has come to our attention that you are delinquent in your
107 February payment. Please remit
108 $392.12 immediately, or your patellae may
109 be needlessly endangered.
110 Love,
113 Mark "Vizopteryx" Dominus
115 Here is a complete program that transforms the example template into
117 the example result, and prints it out:
118 use Text::Template;
120 my $template = Text::Template->new(SOURCE => 'formletter.tmpl')
122 or die "Couldn't construct template: $Text::Template::ERROR";
123 my @monthname = qw(January February March April May June
125 July August September October November December);
126 my %vars = (title => 'Mr.',
127 firstname => 'John',
128 lastname => 'Smith',
129 last_paid_month => 1, # February
130 amount => 392.12,
131 monthname => \@monthname);
132 my $result = $template->fill_in(HASH => \%vars);
134 if (defined $result) { print $result }
136 else { die "Couldn't fill in template: $Text::Template::ERROR" }
137 Philosophy
139 When people make a template module like this one, they almost always
140 start by inventing a special syntax for substitutions. For example,
141 they build it so that a string like "%%VAR%%" is replaced with the
142 value of $VAR. Then they realize the need extra formatting, so they
143 put in some special syntax for formatting. Then they need a loop, so
144 they invent a loop syntax. Pretty soon they have a new little template
145 language.
146 This approach has two problems: First, their little language is
148 crippled. If you need to do something the author hasn't thought of, you
149 lose. Second: Who wants to learn another language? You already know
150 Perl, so why not use it?
151 "Text::Template" templates are programmed in Perl. You embed Perl code
153 in your template, with "{" at the beginning and "}" at the end. If you
154 want a variable interpolated, you write it the way you would in Perl.
155 If you need to make a loop, you can use any of the Perl loop
156 constructions. All the Perl built-in functions are available.
157
159 Template Parsing
160 The "Text::Template" module scans the template source. An open brace
161 "{" begins a program fragment, which continues until the matching close
162 brace "}". When the template is filled in, the program fragments are
163 evaluated, and each one is replaced with the resulting value to yield
164 the text that is returned.
165 A backslash "\" in front of a brace (or another backslash that is in
167 front of a brace) escapes its special meaning. The result of filling
168 out this template:
169 \{ The sum of 1 and 2 is {1+2} \}
171 is
173 { The sum of 1 and 2 is 3 }
175 If you have an unmatched brace, "Text::Template" will return a failure
177 code and a warning about where the problem is. Backslashes that do not
178 precede a brace are passed through unchanged. If you have a template
179 like this:
180 { "String that ends in a newline.\n" }
182 The backslash inside the string is passed through to Perl unchanged, so
184 the "\n" really does turn into a newline. See the note at the end for
185 details about the way backslashes work. Backslash processing is not
186 done when you specify alternative delimiters with the "DELIMITERS"
187 option. (See "Alternative Delimiters", below.)
188 Each program fragment should be a sequence of Perl statements, which
190 are evaluated the usual way. The result of the last statement executed
191 will be evaluated in scalar context; the result of this statement is a
192 string, which is interpolated into the template in place of the program
193 fragment itself.
194 The fragments are evaluated in order, and side effects from earlier
196 fragments will persist into later fragments:
197 {$x = @things; ''}The Lord High Chamberlain has gotten {$x}
199 things for me this year.
200 { $diff = $x - 17;
201 $more = 'more'
202 if ($diff == 0) {
203 $diff = 'no';
204 } elsif ($diff < 0) {
205 $more = 'fewer';
206 }
207 '';
208 }
209 That is {$diff} {$more} than he gave me last year.
210 The value of $x set in the first line will persist into the next
212 fragment that begins on the third line, and the values of $diff and
213 $more set in the second fragment will persist and be interpolated into
214 the last line. The output will look something like this:
215 The Lord High Chamberlain has gotten 42
217 things for me this year.
218 That is 25 more than he gave me last year.
220 That is all the syntax there is.
222 The $OUT variable
224 There is one special trick you can play in a template. Here is the
225 motivation for it: Suppose you are going to pass an array, @items,
226 into the template, and you want the template to generate a bulleted
227 list with a header, like this:
228 Here is a list of the things I have got for you since 1907:
230 * Ivory
231 * Apes
232 * Peacocks
233 * ...
234 One way to do it is with a template like this:
236 Here is a list of the things I have got for you since 1907:
238 { my $blist = '';
239 foreach $i (@items) {
240 $blist .= qq{ * $i\n};
241 }
242 $blist;
243 }
244 Here we construct the list in a variable called $blist, which we return
246 at the end. This is a little cumbersome. There is a shortcut.
247 Inside of templates, there is a special variable called $OUT. Anything
249 you append to this variable will appear in the output of the template.
250 Also, if you use $OUT in a program fragment, the normal behavior, of
251 replacing the fragment with its return value, is disabled; instead the
252 fragment is replaced with the value of $OUT. This means that you can
253 write the template above like this:
254 Here is a list of the things I have got for you since 1907:
256 { foreach $i (@items) {
257 $OUT .= " * $i\n";
258 }
259 }
260 $OUT is reinitialized to the empty string at the start of each program
262 fragment. It is private to "Text::Template", so you can't use a
263 variable named $OUT in your template without invoking the special
264 behavior.
265 General Remarks
267 All "Text::Template" functions return "undef" on failure, and set the
268 variable $Text::Template::ERROR to contain an explanation of what went
269 wrong. For example, if you try to create a template from a file that
270 does not exist, $Text::Template::ERROR will contain something like:
271 Couldn't open file xyz.tmpl: No such file or directory
273 "new"
275 $template = Text::Template->new( TYPE => ..., SOURCE => ... );
276 This creates and returns a new template object. "new" returns "undef"
278 and sets $Text::Template::ERROR if it can't create the template object.
279 "SOURCE" says where the template source code will come from. "TYPE"
280 says what kind of object the source is.
281 The most common type of source is a file:
283 Text::Template->new( TYPE => 'FILE', SOURCE => $filename );
285 This reads the template from the specified file. The filename is
287 opened with the Perl "open" command, so it can be a pipe or anything
288 else that makes sense with "open".
289 The "TYPE" can also be "STRING", in which case the "SOURCE" should be a
291 string:
292 Text::Template->new( TYPE => 'STRING',
294 SOURCE => "This is the actual template!" );
295 The "TYPE" can be "ARRAY", in which case the source should be a
297 reference to an array of strings. The concatenation of these strings
298 is the template:
299 Text::Template->new( TYPE => 'ARRAY',
301 SOURCE => [ "This is ", "the actual",
302 " template!",
303 ]
304 );
305 The "TYPE" can be FILEHANDLE, in which case the source should be an
307 open filehandle (such as you got from the "FileHandle" or "IO::*"
308 packages, or a glob, or a reference to a glob). In this case
309 "Text::Template" will read the text from the filehandle up to end-of-
310 file, and that text is the template:
311 # Read template source code from STDIN:
313 Text::Template->new ( TYPE => 'FILEHANDLE',
314 SOURCE => \*STDIN );
315 If you omit the "TYPE" attribute, it's taken to be "FILE". "SOURCE" is
317 required. If you omit it, the program will abort.
318 The words "TYPE" and "SOURCE" can be spelled any of the following ways:
320 TYPE SOURCE
322 Type Source
323 type source
324 -TYPE -SOURCE
325 -Type -Source
326 -type -source
327 Pick a style you like and stick with it.
329 "DELIMITERS"
331 You may also add a "DELIMITERS" option. If this option is present,
332 its value should be a reference to an array of two strings. The
333 first string is the string that signals the beginning of each
334 program fragment, and the second string is the string that signals
335 the end of each program fragment. See "Alternative Delimiters",
336 below.
337 "ENCODING"
339 You may also add a "ENCODING" option. If this option is present,
340 and the "SOURCE" is a "FILE", then the data will be decoded from
341 the given encoding using the Encode module. You can use any
342 encoding that Encode recognizes. E.g.:
343 Text::Template->new(
345 TYPE => 'FILE',
346 ENCODING => 'UTF-8',
347 SOURCE => 'xyz.tmpl');
348 "UNTAINT"
350 If your program is running in taint mode, you may have problems if
351 your templates are stored in files. Data read from files is
352 considered 'untrustworthy', and taint mode will not allow you to
353 evaluate the Perl code in the file. (It is afraid that a malicious
354 person might have tampered with the file.)
355 In some environments, however, local files are trustworthy. You
357 can tell "Text::Template" that a certain file is trustworthy by
358 supplying "UNTAINT => 1" in the call to "new". This will tell
359 "Text::Template" to disable taint checks on template code that has
360 come from a file, as long as the filename itself is considered
361 trustworthy. It will also disable taint checks on template code
362 that comes from a filehandle. When used with "TYPE => 'string'" or
363 "TYPE => 'array'", it has no effect.
364 See perlsec for more complete information about tainting.
366 Thanks to Steve Palincsar, Gerard Vreeswijk, and Dr. Christoph
368 Baehr for help with this feature.
369 "PREPEND"
371 This option is passed along to the "fill_in" call unless it is
372 overridden in the arguments to "fill_in". See "PREPEND" feature
373 and using "strict" in templates> below.
374 "BROKEN"
376 This option is passed along to the "fill_in" call unless it is
377 overridden in the arguments to "fill_in". See "BROKEN" below.
378 "compile"
380 $template->compile()
381 Loads all the template text from the template's source, parses and
383 compiles it. If successful, returns true; otherwise returns false and
384 sets $Text::Template::ERROR. If the template is already compiled, it
385 returns true and does nothing.
386 You don't usually need to invoke this function, because "fill_in" (see
388 below) compiles the template if it isn't compiled already.
389 If there is an argument to this function, it must be a reference to an
391 array containing alternative delimiter strings. See "Alternative
392 Delimiters", below.
393 "fill_in"
395 $template->fill_in(OPTIONS);
396 Fills in a template. Returns the resulting text if successful.
398 Otherwise, returns "undef" and sets $Text::Template::ERROR.
399 The OPTIONS are a hash, or a list of key-value pairs. You can write
401 the key names in any of the six usual styles as above; this means that
402 where this manual says "PACKAGE" (for example) you can actually use any
403 of
404 PACKAGE Package package -PACKAGE -Package -package
406 Pick a style you like and stick with it. The all-lowercase versions
408 may yield spurious warnings about
409 Ambiguous use of package => resolved to "package"
411 so you might like to avoid them and use the capitalized versions.
413 At present, there are eight legal options: "PACKAGE", "BROKEN",
415 "BROKEN_ARG", "FILENAME", "SAFE", "HASH", "OUTPUT", and "DELIMITERS".
416 "PACKAGE"
418 "PACKAGE" specifies the name of a package in which the program
419 fragments should be evaluated. The default is to use the package
420 from which "fill_in" was called. For example, consider this
421 template:
422 The value of the variable x is {$x}.
424 If you use "$template->fill_in(PACKAGE => 'R')" , then the $x in
426 the template is actually replaced with the value of $R::x. If you
427 omit the "PACKAGE" option, $x will be replaced with the value of
428 the $x variable in the package that actually called "fill_in".
429 You should almost always use "PACKAGE". If you don't, and your
431 template makes changes to variables, those changes will be
432 propagated back into the main program. Evaluating the template in
433 a private package helps prevent this. The template can still
434 modify variables in your program if it wants to, but it will have
435 to do so explicitly. See the section at the end on `Security'.
436 Here's an example of using "PACKAGE":
438 Your Royal Highness,
440 Enclosed please find a list of things I have gotten
442 for you since 1907:
443 { foreach $item (@items) {
445 $item_no++;
446 $OUT .= " $item_no. \u$item\n";
447 }
448 }
449 Signed,
451 Lord High Chamberlain
452 We want to pass in an array which will be assigned to the array
454 @items. Here's how to do that:
455 @items = ('ivory', 'apes', 'peacocks', );
457 $template->fill_in();
458 This is not very safe. The reason this isn't as safe is that if
460 you had a variable named $item_no in scope in your program at the
461 point you called "fill_in", its value would be clobbered by the act
462 of filling out the template. The problem is the same as if you had
463 written a subroutine that used those variables in the same way that
464 the template does. ($OUT is special in templates and is always
465 safe.)
466 One solution to this is to make the $item_no variable private to
468 the template by declaring it with "my". If the template does this,
469 you are safe.
470 But if you use the "PACKAGE" option, you will probably be safe even
472 if the template does not declare its variables with "my":
473 @Q::items = ('ivory', 'apes', 'peacocks', );
475 $template->fill_in(PACKAGE => 'Q');
476 In this case the template will clobber the variable $Q::item_no,
478 which is not related to the one your program was using.
479 Templates cannot affect variables in the main program that are
481 declared with "my", unless you give the template references to
482 those variables.
483 "HASH"
485 You may not want to put the template variables into a package.
486 Packages can be hard to manage: You can't copy them, for example.
487 "HASH" provides an alternative.
488 The value for "HASH" should be a reference to a hash that maps
490 variable names to values. For example,
491 $template->fill_in(
493 HASH => {
494 recipient => "The King",
495 items => ['gold', 'frankincense', 'myrrh'],
496 object => \$self,
497 }
498 );
499 will fill out the template and use "The King" as the value of
501 $recipient and the list of items as the value of @items. Note that
502 we pass an array reference, but inside the template it appears as
503 an array. In general, anything other than a simple string or
504 number should be passed by reference.
505 We also want to pass an object, which is in $self; note that we
507 pass a reference to the object, "\$self" instead. Since we've
508 passed a reference to a scalar, inside the template the object
509 appears as $object.
510 The full details of how it works are a little involved, so you
512 might want to skip to the next section.
513 Suppose the key in the hash is key and the value is value.
515 • If the value is "undef", then any variables named $key, @key,
517 %key, etc., are undefined.
518 • If the value is a string or a number, then $key is set to that
520 value in the template.
521 • For anything else, you must pass a reference.
523 If the value is a reference to an array, then @key is set to
525 that array. If the value is a reference to a hash, then %key
526 is set to that hash. Similarly if value is any other kind of
527 reference. This means that
528 var => "foo"
530 and
532 var => \"foo"
534 have almost exactly the same effect. (The difference is that
536 in the former case, the value is copied, and in the latter case
537 it is aliased.)
538 • In particular, if you want the template to get an object or any
540 kind, you must pass a reference to it:
541 $template->fill_in(HASH => { database_handle => \$dbh, ... });
543 If you do this, the template will have a variable
545 $database_handle which is the database handle object. If you
546 leave out the "\", the template will have a hash
547 %database_handle, which exposes the internal structure of the
548 database handle object; you don't want that.
549 Normally, the way this works is by allocating a private package,
551 loading all the variables into the package, and then filling out
552 the template as if you had specified that package. A new package
553 is allocated each time. However, if you also use the "PACKAGE"
554 option, "Text::Template" loads the variables into the package you
555 specified, and they stay there after the call returns. Subsequent
556 calls to "fill_in" that use the same package will pick up the
557 values you loaded in.
558 If the argument of "HASH" is a reference to an array instead of a
560 reference to a hash, then the array should contain a list of hashes
561 whose contents are loaded into the template package one after the
562 other. You can use this feature if you want to combine several
563 sets of variables. For example, one set of variables might be the
564 defaults for a fill-in form, and the second set might be the user
565 inputs, which override the defaults when they are present:
566 $template->fill_in(HASH => [\%defaults, \%user_input]);
568 You can also use this to set two variables with the same name:
570 $template->fill_in(
572 HASH => [
573 { v => "The King" },
574 { v => [1,2,3] }
575 ]
576 );
577 This sets $v to "The King" and @v to "(1,2,3)".
579 "BROKEN"
581 If any of the program fragments fails to compile or aborts for any
582 reason, and you have set the "BROKEN" option to a function
583 reference, "Text::Template" will invoke the function. This
584 function is called the "BROKEN" function. The "BROKEN" function
585 will tell "Text::Template" what to do next.
586 If the "BROKEN" function returns "undef", "Text::Template" will
588 immediately abort processing the template and return the text that
589 it has accumulated so far. If your function does this, it should
590 set a flag that you can examine after "fill_in" returns so that you
591 can tell whether there was a premature return or not.
592 If the "BROKEN" function returns any other value, that value will
594 be interpolated into the template as if that value had been the
595 return value of the program fragment to begin with. For example,
596 if the "BROKEN" function returns an error string, the error string
597 will be interpolated into the output of the template in place of
598 the program fragment that cased the error.
599 If you don't specify a "BROKEN" function, "Text::Template" supplies
601 a default one that returns something like
602 Program fragment delivered error ``Illegal division by 0 at
604 template line 37''
605 (Note that the format of this message has changed slightly since
607 version 1.31.) The return value of the "BROKEN" function is
608 interpolated into the template at the place the error occurred, so
609 that this template:
610 (3+4)*5 = { 3+4)*5 }
612 yields this result:
614 (3+4)*5 = Program fragment delivered error ``syntax error at template line 1''
616 If you specify a value for the "BROKEN" attribute, it should be a
618 reference to a function that "fill_in" can call instead of the
619 default function.
620 "fill_in" will pass a hash to the "broken" function. The hash will
622 have at least these three members:
623 "text"
625 The source code of the program fragment that failed
626 "error"
628 The text of the error message ($@) generated by eval.
629 The text has been modified to omit the trailing newline and to
631 include the name of the template file (if there was one). The
632 line number counts from the beginning of the template, not from
633 the beginning of the failed program fragment.
634 "lineno"
636 The line number of the template at which the program fragment
637 began.
638 There may also be an "arg" member. See "BROKEN_ARG", below
640 "BROKEN_ARG"
642 If you supply the "BROKEN_ARG" option to "fill_in", the value of
643 the option is passed to the "BROKEN" function whenever it is
644 called. The default "BROKEN" function ignores the "BROKEN_ARG",
645 but you can write a custom "BROKEN" function that uses the
646 "BROKEN_ARG" to get more information about what went wrong.
647 The "BROKEN" function could also use the "BROKEN_ARG" as a
649 reference to store an error message or some other information that
650 it wants to communicate back to the caller. For example:
651 $error = '';
653 sub my_broken {
655 my %args = @_;
656 my $err_ref = $args{arg};
657 ...
658 $$err_ref = "Some error message";
659 return undef;
660 }
661 $template->fill_in(
663 BROKEN => \&my_broken,
664 BROKEN_ARG => \$error
665 );
666 if ($error) {
668 die "It didn't work: $error";
669 }
670 If one of the program fragments in the template fails, it will call
672 the "BROKEN" function, "my_broken", and pass it the "BROKEN_ARG",
673 which is a reference to $error. "my_broken" can store an error
674 message into $error this way. Then the function that called
675 "fill_in" can see if "my_broken" has left an error message for it
676 to find, and proceed accordingly.
677 "FILENAME"
679 If you give "fill_in" a "FILENAME" option, then this is the file
680 name that you loaded the template source from. This only affects
681 the error message that is given for template errors. If you loaded
682 the template from "foo.txt" for example, and pass "foo.txt" as the
683 "FILENAME" parameter, errors will look like "... at foo.txt line N"
684 rather than "... at template line N".
685 Note that this does NOT have anything to do with loading a template
687 from the given filename. See fill_in_file() for that.
688 For example:
690 my $template = Text::Template->new(
692 TYPE => 'string',
693 SOURCE => 'The value is {1/0}');
694 $template->fill_in(FILENAME => 'foo.txt') or die $Text::Template::ERROR;
696 will die with an error that contains
698 Illegal division by zero at at foo.txt line 1
700 "SAFE"
702 If you give "fill_in" a "SAFE" option, its value should be a safe
703 compartment object from the "Safe" package. All evaluation of
704 program fragments will be performed in this compartment. See Safe
705 for full details about such compartments and how to restrict the
706 operations that can be performed in them.
707 If you use the "PACKAGE" option with "SAFE", the package you
709 specify will be placed into the safe compartment and evaluation
710 will take place in that package as usual.
711 If not, "SAFE" operation is a little different from the default.
713 Usually, if you don't specify a package, evaluation of program
714 fragments occurs in the package from which the template was
715 invoked. But in "SAFE" mode the evaluation occurs inside the safe
716 compartment and cannot affect the calling package. Normally, if
717 you use "HASH" without "PACKAGE", the hash variables are imported
718 into a private, one-use-only package. But if you use "HASH" and
719 "SAFE" together without "PACKAGE", the hash variables will just be
720 loaded into the root namespace of the "Safe" compartment.
721 "OUTPUT"
723 If your template is going to generate a lot of text that you are
724 just going to print out again anyway, you can save memory by
725 having "Text::Template" print out the text as it is generated
726 instead of making it into a big string and returning the string.
727 If you supply the "OUTPUT" option to "fill_in", the value should be
728 a filehandle. The generated text will be printed to this
729 filehandle as it is constructed. For example:
730 $template->fill_in(OUTPUT => \*STDOUT, ...);
732 fills in the $template as usual, but the results are immediately
734 printed to STDOUT. This may result in the output appearing more
735 quickly than it would have otherwise.
736 If you use "OUTPUT", the return value from "fill_in" is still true
738 on success and false on failure, but the complete text is not
739 returned to the caller.
740 "PREPEND"
742 You can have some Perl code prepended automatically to the
743 beginning of every program fragment. See ""PREPEND" feature and
744 using "strict" in templates" below.
745 "DELIMITERS"
747 If this option is present, its value should be a reference to a
748 list of two strings. The first string is the string that signals
749 the beginning of each program fragment, and the second string is
750 the string that signals the end of each program fragment. See
751 "Alternative Delimiters", below.
752 If you specify "DELIMITERS" in the call to "fill_in", they override
754 any delimiters you set when you created the template object with
755 "new".
756
758 "fill_this_in"
759 The basic way to fill in a template is to create a template object and
760 then call "fill_in" on it. This is useful if you want to fill in the
761 same template more than once.
762 In some programs, this can be cumbersome. "fill_this_in" accepts a
764 string, which contains the template, and a list of options, which are
765 passed to "fill_in" as above. It constructs the template object for
766 you, fills it in as specified, and returns the results. It returns
767 "undef" and sets $Text::Template::ERROR if it couldn't generate any
768 results.
769 An example:
771 $Q::name = 'Donald';
773 $Q::amount = 141.61;
774 $Q::part = 'hyoid bone';
775 $text = Text::Template->fill_this_in( <<'EOM', PACKAGE => Q);
777 Dear {$name},
778 You owe me \\${sprintf('%.2f', $amount)}.
779 Pay or I will break your {$part}.
780 Love,
781 Grand Vizopteryx of Irkutsk.
782 EOM
783 Notice how we included the template in-line in the program by using a
785 `here document' with the "<<" notation.
786 "fill_this_in" is a deprecated feature. It is only here for backwards
788 compatibility, and may be removed in some far-future version in
789 "Text::Template". You should use "fill_in_string" instead. It is
790 described in the next section.
791 "fill_in_string"
793 It is stupid that "fill_this_in" is a class method. It should have
794 been just an imported function, so that you could omit the
795 "Text::Template->" in the example above. But I made the mistake four
796 years ago and it is too late to change it.
797 "fill_in_string" is exactly like "fill_this_in" except that it is not a
799 method and you can omit the "Text::Template->" and just say
800 print fill_in_string(<<'EOM', ...);
802 Dear {$name},
803 ...
804 EOM
805 To use "fill_in_string", you need to say
807 use Text::Template 'fill_in_string';
809 at the top of your program. You should probably use "fill_in_string"
811 instead of "fill_this_in".
812 "fill_in_file"
814 If you import "fill_in_file", you can say
815 $text = fill_in_file(filename, ...);
817 The "..." are passed to "fill_in" as above. The filename is the name
819 of the file that contains the template you want to fill in. It returns
820 the result text. or "undef", as usual.
821 If you are going to fill in the same file more than once in the same
823 program you should use the longer "new" / "fill_in" sequence instead.
824 It will be a lot faster because it only has to read and parse the file
825 once.
826 Including files into templates
828 People always ask for this. ``Why don't you have an include
829 function?'' they want to know. The short answer is this is Perl, and
830 Perl already has an include function. If you want it, you can just put
831 {qx{cat filename}}
833 into your template. Voilà.
835 If you don't want to use "cat", you can write a little four-line
837 function that opens a file and dumps out its contents, and call it from
838 the template. I wrote one for you. In the template, you can say
839 {Text::Template::_load_text(filename)}
841 If that is too verbose, here is a trick. Suppose the template package
843 that you are going to be mentioning in the "fill_in" call is package
844 "Q". Then in the main program, write
845 *Q::include = \&Text::Template::_load_text;
847 This imports the "_load_text" function into package "Q" with the name
849 "include". From then on, any template that you fill in with package
850 "Q" can say
851 {include(filename)}
853 to insert the text from the named file at that point. If you are using
855 the "HASH" option instead, just put "include =>
856 \&Text::Template::_load_text" into the hash instead of importing it
857 explicitly.
858 Suppose you don't want to insert a plain text file, but rather you want
860 to include one template within another? Just use "fill_in_file" in the
861 template itself:
862 {Text::Template::fill_in_file(filename)}
864 You can do the same importing trick if this is too much to type.
866
868 "my" variables
869 People are frequently surprised when this doesn't work:
870 my $recipient = 'The King';
872 my $text = fill_in_file('formletter.tmpl');
873 The text "The King" doesn't get into the form letter. Why not?
875 Because $recipient is a "my" variable, and the whole point of "my"
876 variables is that they're private and inaccessible except in the scope
877 in which they're declared. The template is not part of that scope, so
878 the template can't see $recipient.
879 If that's not the behavior you want, don't use "my". "my" means a
881 private variable, and in this case you don't want the variable to be
882 private. Put the variables into package variables in some other
883 package, and use the "PACKAGE" option to "fill_in":
884 $Q::recipient = $recipient;
886 my $text = fill_in_file('formletter.tmpl', PACKAGE => 'Q');
887 or pass the names and values in a hash with the "HASH" option:
889 my $text = fill_in_file('formletter.tmpl', HASH => { recipient => $recipient });
891 Security Matters
893 All variables are evaluated in the package you specify with the
894 "PACKAGE" option of "fill_in". if you use this option, and if your
895 templates don't do anything egregiously stupid, you won't have to worry
896 that evaluation of the little programs will creep out into the rest of
897 your program and wreck something.
898 Nevertheless, there's really no way (except with "Safe") to protect
900 against a template that says
901 { $Important::Secret::Security::Enable = 0;
903 # Disable security checks in this program
904 }
905 or
907 { $/ = "ho ho ho"; # Sabotage future uses of <FH>.
909 # $/ is always a global variable
910 }
911 or even
913 { system("rm -rf /") }
915 so don't go filling in templates unless you're sure you know what's in
917 them. If you're worried, or you can't trust the person who wrote the
918 template, use the "SAFE" option.
919 A final warning: program fragments run a small risk of accidentally
921 clobbering local variables in the "fill_in" function itself. These
922 variables all have names that begin with $fi_, so if you stay away from
923 those names you'll be safe. (Of course, if you're a real wizard you
924 can tamper with them deliberately for exciting effects; this is
925 actually how $OUT works.) I can fix this, but it will make the package
926 slower to do it, so I would prefer not to. If you are worried about
927 this, send me mail and I will show you what to do about it.
928 Alternative Delimiters
930 Lorenzo Valdettaro pointed out that if you are using "Text::Template"
931 to generate TeX output, the choice of braces as the program fragment
932 delimiters makes you suffer suffer suffer. Starting in version 1.20,
933 you can change the choice of delimiters to something other than curly
934 braces.
935 In either the new() call or the fill_in() call, you can specify an
937 alternative set of delimiters with the "DELIMITERS" option. For
938 example, if you would like code fragments to be delimited by "[@--" and
939 "--@]" instead of "{" and "}", use
940 ... DELIMITERS => [ '[@--', '--@]' ], ...
942 Note that these delimiters are literal strings, not regexes. (I tried
944 for regexes, but it complicates the lexical analysis too much.) Note
945 also that "DELIMITERS" disables the special meaning of the backslash,
946 so if you want to include the delimiters in the literal text of your
947 template file, you are out of luck---it is up to you to choose
948 delimiters that do not conflict with what you are doing. The delimiter
949 strings may still appear inside of program fragments as long as they
950 nest properly. This means that if for some reason you absolutely must
951 have a program fragment that mentions one of the delimiters, like this:
952 [@--
954 print "Oh no, a delimiter: --@]\n"
955 --@]
956 you may be able to make it work by doing this instead:
958 [@--
960 # Fake matching delimiter in a comment: [@--
961 print "Oh no, a delimiter: --@]\n"
962 --@]
963 It may be safer to choose delimiters that begin with a newline
965 character.
966 Because the parsing of templates is simplified by the absence of
968 backslash escapes, using alternative "DELIMITERS" may speed up the
969 parsing process by 20-25%. This shows that my original choice of "{"
970 and "}" was very bad.
971 "PREPEND" feature and using "strict" in templates
973 Suppose you would like to use "strict" in your templates to detect
974 undeclared variables and the like. But each code fragment is a
975 separate lexical scope, so you have to turn on "strict" at the top of
976 each and every code fragment:
977 { use strict;
979 use vars '$foo';
980 $foo = 14;
981 ...
982 }
983 ...
985 { # we forgot to put `use strict' here
987 my $result = $boo + 12; # $boo is misspelled and should be $foo
988 # No error is raised on `$boo'
989 }
990 Because we didn't put "use strict" at the top of the second fragment,
992 it was only active in the first fragment, and we didn't get any
993 "strict" checking in the second fragment. Then we misspelled $foo and
994 the error wasn't caught.
995 "Text::Template" version 1.22 and higher has a new feature to make this
997 easier. You can specify that any text at all be automatically added to
998 the beginning of each program fragment.
999 When you make a call to "fill_in", you can specify a
1001 PREPEND => 'some perl statements here'
1003 option; the statements will be prepended to each program fragment for
1005 that one call only. Suppose that the "fill_in" call included a
1006 PREPEND => 'use strict;'
1008 option, and that the template looked like this:
1010 { use vars '$foo';
1012 $foo = 14;
1013 ...
1014 }
1015 ...
1017 { my $result = $boo + 12; # $boo is misspelled and should be $foo
1019 ...
1020 }
1021 The code in the second fragment would fail, because $boo has not been
1023 declared. "use strict" was implied, even though you did not write it
1024 explicitly, because the "PREPEND" option added it for you
1025 automatically.
1026 There are three other ways to do this. At the time you create the
1028 template object with "new", you can also supply a "PREPEND" option, in
1029 which case the statements will be prepended each time you fill in that
1030 template. If the "fill_in" call has its own "PREPEND" option, this
1031 overrides the one specified at the time you created the template.
1032 Finally, you can make the class method call
1033 Text::Template->always_prepend('perl statements');
1035 If you do this, then call calls to "fill_in" for any template will
1037 attach the perl statements to the beginning of each program fragment,
1038 except where overridden by "PREPEND" options to "new" or "fill_in".
1039 An alternative to adding "use strict;" to the PREPEND option, you can
1041 pass STRICT => 1 to fill_in when also passing the HASH option.
1042 Suppose that the "fill_in" call included both
1044 HASH => {$foo => ''} and
1046 STRICT => 1
1047 options, and that the template looked like this:
1049 {
1051 $foo = 14;
1052 ...
1053 }
1054 ...
1056 { my $result = $boo + 12; # $boo is misspelled and should be $foo
1058 ...
1059 }
1060 The code in the second fragment would fail, because $boo has not been
1062 declared. "use strict" was implied, even though you did not write it
1063 explicitly, because the "STRICT" option added it for you automatically.
1064 Any variable referenced in the template that is not in the "HASH"
1065 option will be an error.
1066 Prepending in Derived Classes
1068 This section is technical, and you should skip it on the first few
1069 readings.
1070 Normally there are three places that prepended text could come from.
1072 It could come from the "PREPEND" option in the "fill_in" call, from the
1073 "PREPEND" option in the "new" call that created the template object, or
1074 from the argument of the "always_prepend" call. "Text::Template" looks
1075 for these three things in order and takes the first one that it finds.
1076 In a subclass of "Text::Template", this last possibility is ambiguous.
1078 Suppose "S" is a subclass of "Text::Template". Should
1079 Text::Template->always_prepend(...);
1081 affect objects in class "Derived"? The answer is that you can have it
1083 either way.
1084 The "always_prepend" value for "Text::Template" is normally stored in
1086 a hash variable named %GLOBAL_PREPEND under the key "Text::Template".
1087 When "Text::Template" looks to see what text to prepend, it first looks
1088 in the template object itself, and if not, it looks in
1089 $GLOBAL_PREPEND{class} where class is the class to which the template
1090 object belongs. If it doesn't find any value, it looks in
1091 $GLOBAL_PREPEND{'Text::Template'}. This means that objects in class
1092 "Derived" will be affected by
1093 Text::Template->always_prepend(...);
1095 unless there is also a call to
1097 Derived->always_prepend(...);
1099 So when you're designing your derived class, you can arrange to have
1101 your objects ignore "Text::Template::always_prepend" calls by simply
1102 putting "Derived->always_prepend('')" at the top of your module.
1103 Of course, there is also a final escape hatch: Templates support a
1105 "prepend_text" that is used to look up the appropriate text to be
1106 prepended at "fill_in" time. Your derived class can override this
1107 method to get an arbitrary effect.
1108 JavaScript
1110 Jennifer D. St Clair asks:
1111 > Most of my pages contain JavaScript and Stylesheets.
1113 > How do I change the template identifier?
1114 Jennifer is worried about the braces in the JavaScript being taken as
1116 the delimiters of the Perl program fragments. Of course, disaster will
1117 ensue when perl tries to evaluate these as if they were Perl programs.
1118 The best choice is to find some unambiguous delimiter strings that you
1119 can use in your template instead of curly braces, and then use the
1120 "DELIMITERS" option. However, if you can't do this for some reason,
1121 there are two easy workarounds:
1122 1. You can put "\" in front of "{", "}", or "\" to remove its special
1124 meaning. So, for example, instead of
1125 if (br== "n3") {
1127 // etc.
1128 }
1129 you can put
1131 if (br== "n3") \{
1133 // etc.
1134 \}
1135 and it'll come out of the template engine the way you want.
1137 But here is another method that is probably better. To see how it
1139 works, first consider what happens if you put this into a template:
1140 { 'foo' }
1142 Since it's in braces, it gets evaluated, and obviously, this is going
1144 to turn into
1145 foo
1147 So now here's the trick: In Perl, "q{...}" is the same as '...'. So if
1149 we wrote
1150 {q{foo}}
1152 it would turn into
1154 foo
1156 So for your JavaScript, just write
1158 {q{if (br== "n3") {
1160 // etc.
1161 }}
1162 }
1163 and it'll come out as
1165 if (br== "n3") {
1167 // etc.
1168 }
1169 which is what you want.
1171 head2 Shut Up!
1173 People sometimes try to put an initialization section at the top of
1175 their templates, like this:
1176 { ...
1178 $var = 17;
1179 }
1180 Then they complain because there is a 17 at the top of the output that
1182 they didn't want to have there.
1183 Remember that a program fragment is replaced with its own return value,
1185 and that in Perl the return value of a code block is the value of the
1186 last expression that was evaluated, which in this case is 17. If it
1187 didn't do that, you wouldn't be able to write "{$recipient}" and have
1188 the recipient filled in.
1189 To prevent the 17 from appearing in the output is very simple:
1191 { ...
1193 $var = 17;
1194 '';
1195 }
1196 Now the last expression evaluated yields the empty string, which is
1198 invisible. If you don't like the way this looks, use
1199 { ...
1201 $var = 17;
1202 ($SILENTLY);
1203 }
1204 instead. Presumably, $SILENTLY has no value, so nothing will be
1206 interpolated. This is what is known as a `trick'.
1207 Compatibility
1209 Every effort has been made to make this module compatible with older
1210 versions. The only known exceptions follow:
1211 The output format of the default "BROKEN" subroutine has changed twice,
1213 most recently between versions 1.31 and 1.40.
1214 Starting in version 1.10, the $OUT variable is arrogated for a special
1216 meaning. If you had templates before version 1.10 that happened to use
1217 a variable named $OUT, you will have to change them to use some other
1218 variable or all sorts of strangeness will result.
1219 Between versions 0.1b and 1.00 the behavior of the \ metacharacter
1221 changed. In 0.1b, \\ was special everywhere, and the template
1222 processor always replaced it with a single backslash before passing the
1223 code to Perl for evaluation. The rule now is more complicated but
1224 probably more convenient. See the section on backslash processing,
1225 below, for a full discussion.
1226 Backslash Processing
1228 In "Text::Template" beta versions, the backslash was special whenever
1229 it appeared before a brace or another backslash. That meant that while
1230 "{"\n"}" did indeed generate a newline, "{"\\"}" did not generate a
1231 backslash, because the code passed to Perl for evaluation was "\" which
1232 is a syntax error. If you wanted a backslash, you would have had to
1233 write "{"\\\\"}".
1234 In "Text::Template" versions 1.00 through 1.10, there was a bug:
1236 Backslash was special everywhere. In these versions, "{"\n"}"
1237 generated the letter "n".
1238 The bug has been corrected in version 1.11, but I did not go back to
1240 exactly the old rule, because I did not like the idea of having to
1241 write "{"\\\\"}" to get one backslash. The rule is now more
1242 complicated to remember, but probably easier to use. The rule is now:
1243 Backslashes are always passed to Perl unchanged unless they occur as
1244 part of a sequence like "\\\\\\{" or "\\\\\\}". In these contexts,
1245 they are special; "\\" is replaced with "\", and "\{" and "\}" signal a
1246 literal brace.
1247 Examples:
1249 \{ foo \}
1251 is not evaluated, because the "\" before the braces signals that they
1253 should be taken literally. The result in the output looks like this:
1254 { foo }
1256 This is a syntax error:
1258 { "foo}" }
1260 because "Text::Template" thinks that the code ends at the first "}",
1262 and then gets upset when it sees the second one. To make this work
1263 correctly, use
1264 { "foo\}" }
1266 This passes "foo}" to Perl for evaluation. Note there's no "\" in the
1268 evaluated code. If you really want a "\" in the evaluated code, use
1269 { "foo\\\}" }
1271 This passes "foo\}" to Perl for evaluation.
1273 Starting with "Text::Template" version 1.20, backslash processing is
1275 disabled if you use the "DELIMITERS" option to specify alternative
1276 delimiter strings.
1277 A short note about $Text::Template::ERROR
1279 In the past some people have fretted about `violating the package
1280 boundary' by examining a variable inside the "Text::Template" package.
1281 Don't feel this way. $Text::Template::ERROR is part of the published,
1282 official interface to this package. It is perfectly OK to inspect this
1283 variable. The interface is not going to change.
1284 If it really, really bothers you, you can import a function called
1286 "TTerror" that returns the current value of the $ERROR variable. So
1287 you can say:
1288 use Text::Template 'TTerror';
1290 my $template = Text::Template->new(SOURCE => $filename);
1292 unless ($template) {
1293 my $err = TTerror;
1294 die "Couldn't make template: $err; aborting";
1295 }
1296 I don't see what benefit this has over just doing this:
1298 use Text::Template;
1300 my $template = Text::Template->new(SOURCE => $filename)
1302 or die "Couldn't make template: $Text::Template::ERROR; aborting";
1303 But if it makes you happy to do it that way, go ahead.
1305 Sticky Widgets in Template Files
1307 The "CGI" module provides functions for `sticky widgets', which are
1308 form input controls that retain their values from one page to the next.
1309 Sometimes people want to know how to include these widgets into their
1310 template output.
1311 It's totally straightforward. Just call the "CGI" functions from
1313 inside the template:
1314 { $q->checkbox_group(NAME => 'toppings',
1316 LINEBREAK => true,
1317 COLUMNS => 3,
1318 VALUES => \@toppings,
1319 );
1320 }
1321 Automatic preprocessing of program fragments
1323 It may be useful to preprocess the program fragments before they are
1324 evaluated. See "Text::Template::Preprocess" for more details.
1325 Automatic postprocessing of template hunks
1327 It may be useful to process hunks of output before they are appended to
1328 the result text. For this, subclass and replace the
1329 "append_text_to_result" method. It is passed a list of pairs with
1330 these entries:
1331 handle - a filehandle to which to print the desired output
1333 out - a ref to a string to which to append, to use if handle is not given
1334 text - the text that will be appended
1335 type - where the text came from: TEXT for literal text, PROG for code
1336
1338 Originally written by Mark Jason Dominus, Plover Systems (versions 0.01
1339 - 1.46)
1340 Maintainership transferred to Michael Schout <mschout@cpan.org> in
1342 version 1.47
1343
1345 Many thanks to the following people for offering support,
1346 encouragement, advice, bug reports, and all the other good stuff.
1347 • Andrew G Wood
1349 • Andy Wardley
1351 • António Aragão
1353 • Archie Warnock
1355 • Bek Oberin
1357 • Bob Dougherty
1359 • Brian C. Shensky
1361 • Chris Nandor
1363 • Chris Wesley
1365 • Chris.Brezil
1367 • Daini Xie
1369 • Dan Franklin
1371 • Daniel LaLiberte
1373 • David H. Adler
1375 • David Marshall
1377 • Dennis Taylor
1379 • Donald L. Greer Jr.
1381 • Dr. Frank Bucolo
1383 • Fred Steinberg
1385 • Gene Damon
1387 • Hans Persson
1389 • Hans Stoop
1391 • Itamar Almeida de Carvalho
1393 • James H. Thompson
1395 • James Mastros
1397 • Jarko Hietaniemi
1399 • Jason Moore
1401 • Jennifer D. St Clair
1403 • Joel Appelbaum
1405 • Joel Meulenberg
1407 • Jonathan Roy
1409 • Joseph Cheek
1411 • Juan E. Camacho
1413 • Kevin Atteson
1415 • Kevin Madsen
1417 • Klaus Arnhold
1419 • Larry Virden
1421 • Lieven Tomme
1423 • Lorenzo Valdettaro
1425 • Marek Grac
1427 • Matt Womer
1429 • Matt X. Hunter
1431 • Michael G Schwern
1433 • Michael J. Suzio
1435 • Michaely Yeung
1437 • Michelangelo Grigni
1439 • Mike Brodhead
1441 • Niklas Skoglund
1443 • Randal L. Schwartz
1445 • Reuven M. Lerner
1447 • Robert M. Ioffe
1449 • Ron Pero
1451 • San Deng
1453 • Sean Roehnelt
1455 • Sergey Myasnikov
1457 • Shabbir J. Safdar
1459 • Shad Todd
1461 • Steve Palincsar
1463 • Tim Bunce
1465 • Todd A. Green
1467 • Tom Brown
1469 • Tom Henry
1471 • Tom Snee
1473 • Trip Lilley
1475 • Uwe Schneider
1477 • Val Luck
1479 • Yannis Livassof
1481 • Yonat Sharon
1483 • Zac Hansen
1485 • gary at dls.net
1487 Special thanks to:
1489 Jonathan Roy
1491 for telling me how to do the "Safe" support (I spent two years
1492 worrying about it, and then Jonathan pointed out that it was
1493 trivial.)
1494 Ranjit Bhatnagar
1496 for demanding less verbose fragments like they have in ASP, for
1497 helping me figure out the Right Thing, and, especially, for talking
1498 me out of adding any new syntax. These discussions resulted in the
1499 $OUT feature.
1500 Bugs and Caveats
1502 "my" variables in "fill_in" are still susceptible to being clobbered by
1503 template evaluation. They all begin with "fi_", so avoid those names
1504 in your templates.
1505 The line number information will be wrong if the template's lines are
1507 not terminated by "\n". You should let me know if this is a problem.
1508 If you do, I will fix it.
1509 The $OUT variable has a special meaning in templates, so you cannot use
1511 it as if it were a regular variable.
1512 There are not quite enough tests in the test suite.
1514
1516 The development version is on github at
1517 <https://https://github.com/mschout/perl-text-template> and may be
1518 cloned from <git://https://github.com/mschout/perl-text-template.git>
1519
1521 Please report any bugs or feature requests on the bugtracker website
1522 <https://github.com/mschout/perl-text-template/issues>
1523 When submitting a bug or request, please include a test-file or a patch
1525 to an existing test-file that illustrates the bug or desired feature.
1526
1528 Michael Schout <mschout@cpan.org>
1529
1531 This software is copyright (c) 2013 by Mark Jason Dominus
1532 <mjd@cpan.org>.
1533 This is free software; you can redistribute it and/or modify it under
1535 the same terms as the Perl 5 programming language system itself.
1536perl v5.38.0 2023-07-21 Text::Template(3)