NAME
HTML::EP - a system for embedding Perl into HTML
SYNOPSIS
<html><head><title>CGI-Env</title></head>
<ep-comment>
This is an HTML document. You see. Perhaps you wonder about
the unknown HTML tags like ep-comment above? They are part
of the EP system. For example, this comment section will
be removed and you won't see it in your browser.
</ep-comment>
<ep-perl>
# This is an example of embedding Perl into the page.
# We create a variable called time, containing the current
# time. This variable will be used below.
my $self = $_;
$self->{'time'} = localtime(time());
''; # Return an empty string; result becomes embedded into the
# HTML page
</ep-perl>
<body><h1>The current time</h1>
Your HTML::EP system is up and running: The current time is $time$.
</body>
</html>
NEWS
HTML::EP does now have a homepage, a CVS repository and a bug tracking
system. Try
http://html-ep.sourceforge.net/
DESCRIPTION
Have you ever written a CGI binary? Easy thing, isn't it? Was just fun!
Have you written two CGI binaries? Even easier, but not so much fun.
How about the third, fourth or fifth tool? Sometimes you notice that you
are always doing the same:
Reading and parsing variables
Formatting output, in particular building tables
Sending mail out from the page
Building a database connection, passing CGI input to the database and
vice versa
Talking to HTML designers about realizing their wishes
You see, it's soon to become a pain. Of course there are little helpers
around, for example the CGI module, the mod_perl suite and lots of it
more. Using them make live a lot easier, but not so much as you like.
the CGI(3) manpage. the mod_perl(3) manpage.
On the other hand, there are tools like PHP or WebHTML. Incredibly easy
to use, but not as powerfull as Perl. Why not get the best from both
worlds? This is what EP wants to give you, similar to ePerl or
HTML::EmbPerl. I personally believe that EP is simpler and better
extendible than the latter two. the ePerl(1) manpage. the
HTML::EmbPerl(3) manpage.
In short, it's a single, but extensible program, that scans an HTML
document for certain special HTML tags. These tags are replaced by
appropriate output generated by the EP. What remains is passed to the
browser. Its just like writing HTML for an enhanced browser!
Prerequisites
As far as I know EP depends on no system dependent features. However, it
relies on some other Perl modules:
CGI The CGI module should be a part of your Perl core's
installation. If not, you should definitely upgrade to Perl
5.004. :-) My thanks to Lincoln D. Stein
<
[email protected]>. Note, you need a late version,
including the CGI::Cookie module.
HTML::Parser
This module is used for parsing the HTML templates. My
thanks to Gisle Aas <
[email protected]>.
libwww The LWP library contains a lot of utility functions, for example
HTML and URL encoding and decoding. Again, my thanks to
Gisle Aas <
[email protected]>. :-)
Mail::Internet
Graham Barr <
[email protected]> wrote the MailTools package.
Some parts of it, in particular the Mail::Internet module is
used for sending mail from within the HTML page. Thank very
much, Graham!
Storable Raphael Manfredi's <
[email protected]> excellent
Storable module is used for storing sessions. I owe him
much, as Storable is usefull in a lot of other modules.
Perl itself and the above modules are available from any CPAN mirror,
for example
ftp://ftp.funet.fi/pub/languages/perl/CPAN/modules/by-module
Note that you don't need to install these manually, the CPAN module will
help you. See the the section on "Automatic Installation" below.
Automatic Installation
Installing this module (and the prerequisites from above) is quite
simple, if you have the CPAN module available and network access, you
might try an automatic installation:
perl -MCPAN -e shell
If the CPAN prompt appears, asking you for commands, enter
install Bundle::HTML::EP
Manual Installation
If automatic installation doesn't work, you just fetch the archive,
extract it with
gzip -cd HTML-EP-0.1125.tar.gz | tar xf -
(this is for Unix users, Windows users would prefer WinZip or something
similar) and then enter the following:
cd HTML-EP-0.1125
perl Makefile.PL
make
make test
If any tests fail, let me know. Otherwise go on with
make install
This will put the required Perl modules into a destination where Perl
finds it by default. Additionally it will install a single CGI binary,
called `ep.cgi'.
The docs are available online with
perldoc HTML::EP
If you prefer an HTML version of the docs, try
pod2html lib/HTML/EP.pm
in the source directory.
Using the CGI binary
You have different options for integrating EP into your WWW server,
depending on which server you are using and the permissions you have.
The simplest possibility is running an external CGI binary. Another
option is to use mod_perl with Apache, see the section on "Using
mod_perl" below.
I suggest that you choose an extension and configure your WWW server for
feeding files with this extension into `ep.cgi'. For example, with
Apache, you can add the following lines to your `srm.conf':
ScriptAlias /cgi-bin/ep.cgi /usr/bin/ep.cgi
AddType x-ep-script .ep
Action x-ep-script /cgi-bin/ep.cgi
This tells Apache that files with extension ep.cgi are handled by the
CGI binary `/usr/bin/ep.cgi'. Make sure, that the ScriptAlias line is
entered *before* any other ScriptAlias instruction! In particular, the
following would be wrong:
ScriptAlias /cgi-bin/ /home/httpd/cgi-bin/
...
ScriptAlias /cgi-bin/ep.cgi /usr/bin/ep.cgi
The first rule would be applied before our rule, so that it could never
match.
From now on your server will never return files with extension .ep
directly! Verify your installation by creating the following file:
<html><head><title>Local time</title></head>
<body>
The current time is:
<ep-perl>scalar(localtime(time))</ep-perl>
</body>
(Note that this is a much shorter version of the example in the
synopsis.) Store it as `/test.ep' on your web server and retrieve the
file via your Web server. If you see the time displayed, you are up and
running.
Using mod_perl
The EP package can be integrated into mod_perl, for example by using the
following commands in `srm.conf':
PerlModule Apache::EP
<Files *.ep>
SetHandler perl-script
PerlHandler Apache::EP->handler
Options ExecCGI
</Files>
Keep in mind, that mod_perl differs in many details from programming CGI
binaries. In particular you might need to restart Apache for loading
changes in modules.
Using the Internet Information Server
I am sure there is a better way of installation, in the sense of
mod_perl, however, I am no IIS expert. I can only recommend using Perl
as an external binary, in the sense of CGI.
The idea is to advice the IIS, that files with extension .ep have to be
executed by running
C:\Perl\bin\perl.exe c:\Perl\bin\ep.cgi %s%s
with %s%s being the path to the EP document. (Of course the paths have
to be adjusted to your local Perl.) This can be done by creating a new
extension in the window "Base directory/Configure". (Window name
translated from the german IIS, it�s "Basisverzeichnis / Konfigurieren"
here and might be different in english.)
Available methods
All EP tags are starting with the prefix *ep-*. Some available tags are:
ep-comment
This is a multi-line tag for embedding comments into your HTML page.
But why use this tag, instead of the usual HTML comment, `<!--'? The
difference is, that the user will never see the former.
Example:
<html>
<!-- This is a comment. I like comments. --!>
<ep-comment>
This is another comment, but you won't see it
in your browser. The HTML editor will show it
to you, however!
</ep-comment>
</html>
Do not try to embed EP instructions into the comment section! They
won't produce output, but they might be executed anyways.
ep-perl
This is for embedding Perl into your script. There are two versions
of it: A multiline version is for embedding the Perl code
immediately into your script. Example:
<html>
<head><title>The Date</title></head>
<body>
<h1>The Date</h1>
<p>Hello, today its the</p>
<p align=center>
<ep-perl>
# This little piece of Perl code will be executed
# while scanning the page.
#
# Let's calculate the date!
#
my($sec,$min,$hour,$mday,$mon,$year)
= localtime(time);
# Leave a string with the date as result. Will be
# inserted into the HTML stream:
sprintf("%02d.%02d.%04d", $mday, $mon+1, $year+1900);
</ep-perl>
</p>
</body>
</html>
If you don't like to embed Perl code, you may store it into a
different file. That's what the single-line version of ep-perl is
for:
<html>
<head><title>The Date</title></head>
<body>
<h1>The Date</h1>
<p>Hello, today its the</p>
<p align=center>
<ep-perl src="date.pl">
</p>
</body>
</html>
You have noticed, that the little script's result was inserted into
the HTML page, did you? It did return a date, in other words a
string consisting of letters, digits and dots. There's no problem
with inserting such a string into an HTML stream.
But that's not always the case! Say you have a string like
Use </html> for terminating the HTML page.
This cannot be inserted as a raw string, for obvious reasons. Thus
the ep-perl command has an attribute *output*. Use it like this:
<ep-perl output=html>
'Use </html> for terminating the HTML page.';
</ep-perl>
Possible values of the *output* attribute are `raw' (default),
`html' (HTML encoded) and `url' (URL encoded).
It's a common mistake, to use the Perl command `return' in embedded
Perl. Never do that! If you need return (there are of course
situations where returning can help), do it like this:
<ep-perl>
sub eval_me {
if ($this) {
return 'foo';
} elsif ($that) {
return 'bar';
}
'';
}
eval_me();
</ep-perl>
See the section on "Variables" below for interactions between Perl
variables and EP variables.
For security reasons, you might set an attribute *safe*, as in
<ep-perl safe=1>...</ep-perl>
This will create a Safe compartment for you and run the embedded
script in the compartment. Using this attribute is highly
recommended!
ep-mail
This command will send an e-mail. The attributes will be used for
creating the email header, in particular the `subject', `from' and
`to' attribute should be used. Example:
<ep-mail subject="Howdy!" from="
[email protected]"
reply-to="
[email protected]" to="
[email protected]">
Hello, Bill, old chap. How are you?
Yours sincerely,
Jochen
</ep-mail>
You can still use EP variables in the E-mail body, for example the
following works:
<ep-mail subject="Test" reply-to="$cgi->email$" to="
[email protected]"
from="
[email protected]">
Hello, Joe,
this e-mail was sent to you by $@cgi->name$.
</ep-mail>
But note that we suppress conversion into HTML format in the mail
body! See the section on "Variables" below for details.
Recent sendmail versions are quite picky about validity of email
addresses. Thus it is highly recommended that you use valid
addresses for the *to* and *from* fields. If you want to customize
the sender, you'd better choose a fixed *from* field and modify the
*reply-to* field only, as in the example above.
ep-errhandler
This command advices EP, what to do in case of errors. See the
section on "Error handling" below. Example:
<ep-comment>
Set the template being used for system errors.
</ep-comment>
<ep-errhandler type=system src=/templates/syserr.html>
<ep-comment>
Likewise, set the template for user errors.
</ep-comment>
<ep-errhandler type=user src=/templates/usererr.html>
If an error occurs, the given scripts are loaded and used as
templates instead of the current one. You don't need external files!
Instead you can use
<ep-errhandler type=user>
<HTML><HEAD><TITLE>User error</TITLE></HEAD>
<BODY><H1>User error</H1>
<P>Replace user and continue. :-)</P>
<P>To be serious, the following problem happened:</P>
<PRE>$errmsg$</PRE>
<P>Please return to the calling page, fix the problem
and retry.</P>
</BODY></HTML>
</ep-errhandler>
However, you might prefer to use a single error template and of
course it's faster to use external error templates than parsing
builtin templates. (At least, if no error occurs. :-)
ep-error
This command forces an error message. See the section on "Error
handling" below. You can trigger user or system errors by setting
the *type* attribute to the values `system' (default) or `user'. The
*msg* attribute is for setting the error message.
Example:
<ep-comment>
If no email address was entered, force a user error.
</ep-comment>
<ep-if eval="$cgi->email$">
Email address is ok.
<ep-else>
<ep-error msg="Missing email address" type=user>
</ep-if>
ep-database
This command connects to a database. Its attributes are `dsn',
`user' and `password' corresponding to the same attributes of the
DBI connect method. See the DBI(3) manpage for details on DBI.
Example:
<ep-database dsn="DBI:mysql:test" user="joe"
password="Authorized?Me?">
You can use different database connections by using the *dbh*
attribute:
<ep-database dbh="dbh2" dsn="DBI:mSQL:test">
The *dbh* attribute advices EP to store the DBI handle in the given
variable. (Default: `dbh') See the section on "Variables" below.
ep-query
This command executes an SQL statement. The `query' attribute will
be used for passing the SQL statement. Of course a multiline version
is available, thus
<ep-query statement="INSERT INTO foo VALUES (1, 'bar')">
is the same as
<ep-query>
INSERT INTO foo VALUES (1, 'bar')
</ep-query>
If your query retrieves a result, use the `result' attribute to
store it in a variable, for example like this:
<ep-query statement="SELECT * FROM employees" result="employees"
resulttype="hash" startat=0 limit=-1>
This will create a variable `employees', an array ref of hash refs.
You can use the ep-list command for displaying the output. See the
section on "Variables" below.
When using multiple database connections, use the *dbh* attribute
for choosing the connection. (See the *ep-database* method above.)
If you have big result tables, you might prefer DBI's
*fetchrow_arrayref* method over creating hash refs, because arrays
are created faster than hash refs. This is achieved by setting the
attribute *resulttype* to array. The default is hash. Other
resulttypes are *single_hash* and *single_array*: If your query will
return at most a single element, then the result variable will
contain the first row (or an undefined value) and not an array.
Sometimes you don't want to retrieve the complete result table. In
that case you can use the attributes *startat* and *limit*. For
example, to retrieve rows 0-19, use startat=0 and *limit=20*.
Likewise you would use startat=20 and limit=20 for rows 20-39.
When using the *MySQL* engine, the *startat* and *limit* attributes
are directly mapped to MySQL's *LIMIT* clause.
ep-list
This command is used to display an array of refs. Lets assume, that
the variable `employees' contains a an array ref of refs with the
attributes *name* and *department*. Then you could create a table of
employees as follows:
<table><tr><th>Nr.</th><th>Name</th><th>Department</th>
<ep-list items="employees" item="e">
<tr><td>$i$</td><td>$e->name$</td><td>$e->department$</td>
</ep-list>
</table>
This will be processed as follows: For any item in the array,
retrieved from the variable `employees', create a variable `e' and
display the text between ep-list and /ep-list for it by replacing
the patterns $e->name$ and $e->department$ with the corresponding
values.
The variable *i* is initially set to 0 and incremented by one with
any element.
As an alternative to the *items* attribute, you may prefer the
*range* attribute: For example
<ep-list range="1..12" item=month><OPTION>$month$</ep-list>
will create the options array of a select box for you, where the
user can select a month. If your prefer month names, you may better
choose
<ep-list range="jan,feb,mar,apr,jun,jul,aug,sep,oct,nov,dec"
item=month><OPTION>$month$</ep-list>
It is even possible to mix both versions, as in
<ep-list range="1..3,6..7,10" item=m><OPTION>$m$</ep-list>
See the *ep-select* command below for another example of the *range*
attribute.
It is possible to nest multiple ep-list statements, as in
<ep-list range="1..3" item="i"><ep-list range="4..6"
item="j">$i$$j$ </ep-list></ep-list>
This will create the output "14 15 16 24 25 26 34 35 36".
ep-select
This is similar to ep-list, but it is specifically designed for
creating SELECT boxes and similar things. We explain it by example:
<ep-select name="year" range="1991..1995" item="y"
selected="$cgi->year$">
<OPTION $selected$>$y$</ep-select>
If you supply a *selected* attribute, then a variable *selected*
will be created for any item. The value will be either an empty
string or the word `SELECTED' (configurable via the attribute
*selected-text*), depending on whether the item matches the
*selected* value or not.
ep-input
This is usefull for reading an objects data out of CGI variables.
Say you have a form with input fields describing an address, the
field names being address_t_name, address_t_street, address_n_zip
and address_t_city. By using the command
<ep-input prefix="address_" dest="address">
the EP program will create a variable "address" for you which is an
hash ref as follows:
$cgi = $_->{cgi};
$_->{address} = {
name => { col => 'name',
val => $cgi->param("address_name"),
type => 't',
},
street => { col => 'street',
val => $cgi->param("address_street"),
type => 't',
},
zip => { col => 'zip',
val => $cgi->param("address_zip"),
type => 'n',
},
city => { col => 'city',
val => $cgi->param("address_city"),
type => 't'
}
};
In general column names beginning with *address* will be splitted
into `prefix_type_suffix', the type being one of
t Text columns (CHAR, VARCHAR, BINARY, or whatever), that will be
quoted using the $self->{'dbh'}->quote() method.
n Numeric columns (INTEGER, REAL, ...) that will be left untouched
dd
dm
dy Day, month and year of a date. The combined fields will be
quoted as 'yyyy-mm-dd'.
s Set columns as created using MultiSelect boxes; the selected
values will be used for creating a comma separated string.
The idea is generating SQL queries automatically out of the
`address' variable. This task is supported by the *sqlquery*
attribute:
<ep-database dsn="DBI:mysql:test">
<ep-input prefix="address_" dest="a" sqlquery=1>
<ep-comment>Create a new record, if no ID is given</ep-comment>
<ep-if eval="$cgi->id$">
<ep-query
statement="INSERT INTO addresses ($@a->names$) VALUES ($@a->values$)">
<ep-else>
<ep-query
statement="UPDATE addresses SET $@a->update$ WHERE id = $@id$">
The *sqlquery* creates attributes *names*, *values* and *update* for
you, that may be used in INSERT or UPDATE queries. Note that the
*ep-input* must be preceeded by an *ep-database* call, because it is
using DBI's *quote* method. the DBI(3) manpage.
There are situations where you want to fetch not only a single
object, but a list of objects. Suggest an order form of articles.
Then you might have input fields *art_0_t_name*, *art_0_n_count*,
*art_0_n_price*, *art_1_t_name*, ...
In that case you can give the *ep-input* command an attribute list,
like this:
<ep-input prefix="art_" dest="art" list=1>
The module will read an array ref of objects to the variable `dest'.
Any object will have an additional scalar variable `i' referring to
the items number, beginning with 0. In other words, you can process
the order form as follows:
<ep-input prefix="art_" dest="art" list=1>
<ep-perl>
my $self = $_;
my $sum = 0.0;
for (my $i = 0; defined($self->{cgi}->param("art_$i_n_count"));
$i++) {
$sum += $self->{cgi}->param("art_$i_n_count") *
$self->{cgi}->param("art_$i_n_price")
}
''
</ep-perl>
<ep-mail from="$cgi->email$" to="order@mydomain"
subject="Order form">
The following items have been ordered:
Nr. Price Article
<ep-list>
$art->count->val$ $art->price->val$ $art->name->val$
</ep-list>
Total sum: $sum$
</ep-mail>
ep-input-sql-query
<ep-input-sql-query dest=art>
This method is internally called by ep-input and implements the
creation of the *names*, *values* and *updates* attributes.
It takes as input the hash ref given by the variable *dest*, usually
created by ep-input. The hash ref consists of column names as keys
and hash refs with the attributes *type* and *val*.
The main reason for putting this into a separate method is
subclassing: It is quite usual, that you want ep-input to read the
data, then do some verification and/or modification on the data (for
example, canonicalizing dates) and finally create the SQL query.
This can be done quite easily by subclassing the
*_ep_input_sql_query* method: Within the method you verify and/or
modify data entered by the user and then call the super class.
For example, a typical subclass implementation could look like this:
sub _ep_input_sql_query {
my $self = shift; my $attr = shift;
# If the user left the MYCOL column empty, set it to NULL.
my $dest = $attr->{'dest'};
$self->{$dest}->{'MYCOL'} = undef
if $self->{$dest}->{'MYCOL'} eq '';
$self->SUPER::_ep_input_sql_query($attr);
}
ep-include
Sometimes you want to source external files. This can be done by
using
<ep-include file="myfile">
If a file with the given name doesn't exist, the file name is
treated as being relative to your WWW servers *DOCUMENT_ROOT*
directory.
ep-exit
This directive terminates processing of the current HTML page.
Conditional HTML
It is possible to blank out parts of the HTML document. See the
following example:
<html><head><title>Conditional HTML</title></head>
<body>
<h1>Conditional HTML</h1>
<ep-if eval="$_->{cgi}->param('i') < 0">
You have entered a negative number for i!
<ep-else eval="$_->{cgi}->param('i') == 0">
You have entered zero for i!
<ep-else>
<ep-if eval="$_->{cgi}->param('j') < 0">
You have entered a negative number for j!
<ep-else eval="$_->{cgi}->param('h') == 0">
You have entered zero for j!
<ep-else>
Ok, both numbers are positive.
</ep-else>
</ep-else>
</body>
</html>
The example is of course somewhat unnatural, because you'd better use a
single ep-perl in that case, but it shows that we can use arbitrary
complex structures of conditional HTML.
The *eval* attribute is simply treated as a truth value, as in Perl.
Thus empty strings or numeric zeros are FALSE, everything else is TRUE.
This is reversed, if you replace *eval* with *neval*:
<ep-if neval="$a$">
a is not set
<ep-else>
a is set
</ep-if>
If you'd like to compare numeric values, use the *cnd* attribute, as in
<ep-if cnd="$a$<$b$">
a is lower than b
<ep-else>
a is greater than or equal to b
</ep-if>
You may choose either of ==, !=, <, >, <= or >= for the condition. And
finally you may compare string values like this:
<ep-if cnd="'$a$' eq '$b$'">
a is equal to b
</ep-if>
Note the use of the single quotes, which is really required here.
Available conditions are eq and ne.
As with ep-list, you may nest multiple ep-if's or combine them with ep-
list. The following is invalid, though:
<ep-list range="1..3" item="i">
<ep-if cnd="$i$<3">ok</ep-list></ep-if>
As the ep-if starts within the ep-list, it must also be terminated
before the corresponding /ep-list.
Localization
Localization is available via the HTML::EP::Locale module. Currently it
only offers methods for localizing strings.
To access the module, let's assume you prefer your visitors reading the
german (de) version of your page, but it is also available in english
(en). Then start your HTML page with
<ep-package name="HTML::EP::Locale" accept-language="de,en">
When the package is loaded, it tries to guess your documents language.
The default language is *de* (german) or whatever you choose when
installing the package. Another language can be specified by
* By setting the CGI variable *language*, for example by making a link
to mypage.ep?language=en.
* By setting the environment variable *HTTP_ACCEPT_LANGUAGE*; most
browsers do this for you. For example with Netscape, this
variable is configurable via
Edit/Preferences/Navigator/Languages.
Two possibilities are available for localizing strings. For short
strings like titles, headers or Link refs you might prefer this version:
<ep-language de="Titel" en="Title">
Obviously this is not appropriate for longer strings and it must not
contain HTML patterns. Thus another version is available:
<ep-language language=de>
<p>Dies ist ein Absatz.</p>
<p>Dies ist der zweite Absatz.</p>
<ep-language language=en>
<p>This is one paragraph.</p>
<p>This is another paragraph.</p>
</ep-language>
Note you need not use a /ep-language for terminating the german part,
similar to the ep-if, ep-elseif, ..., ep-else, /ep-if structure.
A special problem with localization is the choice of a character set.
You can fix a certain character set with something like
<META HTTP-EQUIV="Content-type"
CONTENT="text/html; CHARSET: iso-8859-2">
Error handling
Error handling with EP is quite simple: All you do in case of errors is
throwing a Perl exception. For example, DBI handles are created with the
RaiseError attribute set to 1, so that SQL errors trigger a Perl
exception. You never care for errors!
However, what happens in case of errors? In that case, EP will use the
template that you have set with ep-errhandler and treat it like an
ordinary EP document, by setting the variables `errmsg' and `admin'.
If you don't set an error handler, the following template will be used,
which is well suited for creating an own error template:
<html><head><title>Internal error</title></head>
<body><h1>Internal error</h1>
<p>An internal error occurred. The server has not been able to
fullfill your request. The error message is:</p>
<pre>
$errmsg$
</pre>
<p>Please contact the Webmaster,
<a href="mailto:$admin$">$admin$</a>,
tell him the URL, the time and error message.
</p>
<p>We apologize for any inconvenience, please try again later!</p>
<br><br><br><p>Yours sincerely,</p><p>The Webmaster</p>
</body>
</html>
Variables
It is important to understand, how EP variables work, in particular when
working with ep-perl.
You always have an object $_, which is an instance of the HTML::EP class
(a subclass of HTML::Parser). This object has certain attributes, in
particular `$_->{cgi}', a CGI object and `$_->{dbh}', the DBI handle.
(Of course valid after `ep-database' only.) If you want to set or modify
a variable, you have to set `$_->{varname}'. If you want to retrieve the
value, use the same. Note that you cannot use `$_' for a long time, as
it will be changed by Perl loops and the like, thus your Perl code
typically starts with
$_ = $self;
But how do you access the variable from within EP documents? You just
write
$varname$
This will be replaced automatically by the parser with the value of `$_-
>{varname}'. Even more, the value will be converted into HTML source!
If `varname' is a structured variable, for example a hash or array ref,
you may as well use
$varname->attrname$
or
$varname->0$
to access `$_->{varname}->{attrname}' or `$_->{varname}->[0]',
respectively. A special value of *varname* is `cgi': This will access
the CGI variable of the same name, thus the following are equivalent:
$cgi->email$
and
$_->{cgi}->param('email');
But what, if you don't want your variable to be HTML encoded? You may as
well use
$@varname$ (Raw)
$#varname$ (URL encoded)
$~varname$ (SQL encoded)
The latter uses the $_->{dbh}->quote() method. In particular this
implies that you have to be connected to a database, before using this
tag!
You can even use these symbols in attributes of EP commands. For
example, the following will be usefull when sending a mail:
<ep-mail subject="Howdy!" from="$@cgi->email$"
to="
[email protected]">
Attributes may include EP variables, just like ordinary HTML code. Even
more, they may contain Perl code which is evaluated just like code
between `<ep-perl>' and `</ep-perl>'. However, you need to use the
variable `$_' in the code, because the package otherwise doesn't detect
what you want it to do.
See the section on "Custom variable formatting" for setting up your own
formats.
Of course you can set EP variables from within an ep-perl section. But
sometimes it is desirable to set them from within HTML. In such cases
you can do something like
<ep-set var="a" val="b">
Now, if you do a
Variable a has the value $a$.
the value b will be emitted. It is also possible to set multiline
variables:
<ep-set var="a">
This is a template, extending a single line.
</ep-set>
Custom variable formatting
Sometimes the builtin formatting methods of HTML::EP are not sufficient.
A good example are currencies. These can be handled with format methods.
For example, see the following method for german currency values:
<ep-package name="MyPackage">
<ep-perl>
package MyPackage;
sub _format_DM {
my($self, $val) = @_;
sprintf("%.2f DM", $val);
$val =~ s/\./,/;
$val;
};
''
</ep-perl>
This can be used as follows, suggest we have the following variables:
a = 1
b = 2.4
c = 34.47
then we can use
a = $&DM->a$ => 1,00 DM
b = $&DM->b$ => 2,40 DM
c = $&DM->c$ => 34,47 DM
In other words: Use the special marker &, followed by the custom formats
method name, the dereferencing operator and finally the variable name.
The above method is already predefined by the HTML::EP::Locale module.
As you have seen, the pattern $&METHODNAME->var$ triggers the call of
$self->_format_METHODNAME($self->{'var'});
It is not always usefull to fix a method name. In such cases you may
instead store a code ref in
Modifying the CGI headers
The attribute $self->{'_ep_heaaders'} is containing arguments that you
want to pass to CGI->header(). Use it like this:
<ep-perl>
$_->{'_ep_headers'} = { '-status' => '402 Payment required',
'-expires' => '+3d'
}
</ep-perl>
Doing a redirect
A redirect is moving the browser to another page without actually
displaying the current page. You can do it like this:
<ep-redirect target="
http://other.server/other/page">
Producing Non-HTML
Say you want a CGI binary that creates a gif and not an HTML document.
(See the `ifgif.ep' file from the SNMP::Monitor distribution for an
example.) Two problems are arising here: First of all you have to create
your own headers. Next you *must* prevent that EP is emitting any
output, because this might trash your images validity. Here's what to
do:
<ep-perl>
my $self = $_;
my $cgi = $self->{'cgi'};
$self->_ep_database({'dsn' => 'DBI:mysql:test',
'user' => 'joe',
'password' => 'joe'});
$self->_ep_query({'statement' => "SELECT image FROM images WHERE"
. " id = " . $cgi->param('id'),
'result' => 'im',
'resultype' => 'single_hash'});
$self->print($cgi->header('-type' => 'image/gif'),
$self->{im}->{'image'});
$self->Stop();
</ep-perl>
Note the use of $self->Stop()!
NPH Scripts
The Apache server and other WWW servers have a nice feature that allows
you to return HTML pages line by line: If your script is called
something like nph-myscript then the server is passing the scripts
output to the browser immediately. This is usefull, for example, if you
display the output of a traceroute command: You'd like to see any line
immediately, but it may take some time untill the next line arrives.
Unfortunately NPH scripts are not well suited for HTML::EP: One of EP's
major targets is that you need not care for errors: They may occur at
any point but are still catched and handled by creating an error
message. However, there's no other way to guarantee this without
buffering output until the script ends.
If you really need to use NPH, do it like this:
<ep-perl>
my $self = $_;
local $| = 1; # make sure that Perl isn't buffering
$self->print($self->{'cgi'}->header('-type' => 'text/html',
'-nph' => 1));
for (my $i = 0; $i < 20; $i++) {
$self->print("This is line $i. Waiting one second ...\n")
sleep 1;
}
$self->Stop();
</ep-perl>
Note, that *no* more output will be produced by EP after calling $self-
>Stop()!
DEBUGGING
Debugging CGI applications is always a problem. The EP module does its
best to support you.
Whenever you supply a CGI variable *debug*, then the module will enter
debugging mode. For example if your document is `/mypage.ep', then tell
your browser to fetch `/mypage.ep?debug=1'. You won't see the usual HTML
page, but a plain text page with lots of debugging messages and the
created HTML source.
You may extend the debugging code with sequences like
<ep-perl>
my $self = $_;
$self->print("I'm here!\n") if $self->{debug};
</ep-perl>
Note that you should not call the *print* function directly, but the
*print* method! The former works well in CGI environments, but EP should
work even in other environments as well.
But sometimes this is not sufficient: What's inserting debugging
messages compared to using the Perl debugger? In that case you can
emulate a CGI environment as follows:
export DOCUMENT_ROOT=/usr/local/www/htdocs
export PATH_TRANSLATED=$DOCUMENT_ROOT/mypage.ep
export REQUEST_METHOD=GET
export QUERY_STRING="var1=val1&var2=val2"
perl -d /usr/bin/ep.cgi
This allows you single-stepping through your program, displaying
variable values and the like.
However, the debug variable is obviously a security problem. For that
reason the *debughosts* variable is present in HTML::EP::Config: You
should set it to a regular expression matching the IP numbers of hosts
that are allowed to enable debugging mode. The Makefile.PL should query
for appropriate settings automatically while running.
EXAMPLES
The program comes with a set of examples incorporated. These are:
- A simple Unix user administration in examples/admin.
- A generic frontend for editing DBI tables in examples/edit.ep
- A POP3 client for the web in examples/pop3.
Other examples are:
- The SNMP monitor, a utility for watching, logging and displaying
interface utilization and status of network interfaces via WWW.
See the directory authors/id/JWIED on any CPAN mirror, for example
ftp://ftp.funet.fi/pub/languages/perl/CPAN.
- The EP Explorer, an application I wrote for managing printer queues
on a Unix hosts. The user can select a file for printing it, much
like he did within the Windows explorer. Likewise, he can watch
the printer status.
- The HTML::EP::Glimpse package, a simple search engine based on
Glimpse. (In other words, some flavour of WebGlimpse, which is
much simpler to install and maintain and allows a free design.)
EXTENSIONS
It is quite easy to write own methods.
Single line extensions
For example, suggest you want a method for setting EP variables:
<ep-set var="e" value=1>
Once the variable is created, you can access it via
$e$
This can be done like this:
<ep-perl package="HTML::EP">
# Write a handler for ep-env:
sub _ep_set ($$) {
my($self, $attr) = @_;
my $var = $attr->{'var'};
my $val = $attr->{'value'};
$self->{$var} = $val;
'';
}
# Return an empty string:
'';
</ep-perl>
Note that we used the name _ep_set: By default the EP module takes the
method name (ep-env in out case) translates all hyphens to underscores
and adds a leading underscore. We'll see in the next section how you can
override this behaviour.
Multi line extensions
But how to write methods, that use a `<tag>' .. `</tag>' syntax? As an
example, we write a method for creating external files. The method
receives two attributes, a *file* attribute for the files name and a
*contents* attribute for the files contents. The method can be used in
two ways:
<ep-file file="test.dat" contents="Hi!">
or like this, in multiline mode:
<ep-file file="test.dat">
Hi!
</ep-file>
Here it is:
<ep-perl package="HTML::EP">
# Write a handler for ep-file:
sub _ep_file {
my $self = shift; my $attr = shift;
my $contents = $self->AttrVal($attr->{'contents'}, @_);
my $file = $attr->{'file'};
require Symbol;
my $fh = Symbol::gensym();
(open($fh, ">$file) && (print $fh $contents) &&
close($fh)) or die "Error while creating $file: $!";
'';
}
# Return an empty string:
'';
</ep-perl>
The main difference to the previous example is that our method is that a
special attribute (*contents*) is defined, that may be passed as part of
the ep-file statement. However, if you don't define it as part of the
statement, the *AttrVal* method reads more text from the document untill
it finds a matching /ep-file.
Note the use of the *Symbol* package when accessing files: *Never* use
global handles like
open(FILE, ...)
as this might break future multithreading code!
The above example works well, if you don't need to nest your statement.
If this should be the case, you need to deal with EP's token streams.
See the ep-if and ep-list methods for examples.
External extensions
So far we have discussed only minor extensions that we did install as
part of HTML::EP. However, this is somewhat dangerous with mod_perl:
Suggest you have multiple virtual hosts. It might happen, that virtual
host www.foo.com defines a method ep-file, but www.bar.net defines
another. We'd have an immediate name space clash.
To prevent such a namespace pollution, EP supports external extensions
with an inheritage model that is borrowed from Perl. Suggest we write a
Shop extension. Of course this extension borrows from HTML::EP::Session.
Thus we have the following class design:
Shop ---isa---> HTML::EP::Session ---isa---> HTML::EP
We start writing our Shop extension like any other Perl package:
package Shop;
@Shop::ISA = qw(HTML::EP::Session); # HTML::EP::Session inherits
# from HTML::EP
sub _ep_shop_session {
my($self, $attr) = @_;
# Initialize the session
...
'';
}
sub init {
my $self = shift;
if (!$self->{'_ep_shop_initialized'}) {
$self->{'_ep_shop_initialized'} = 1;
$self->SUPER::init();
# Do something here
...
}
}
In the HTML page we load this package as follows:
<ep-package name="Shop">
<ep-shop-session>
This will do a require Shop, bless the object $self into the class
*Shop* and call $self-init()>. Note that we allow the init method to be
called more than once, this is important for stacking packages.
By default packages are loaded from Perl's system directories. You can
use the attribute *lib* to add private directories to the library search
path. This can be relative to the servers document root, as in
<ep-package name="Shop" lib="/perl-lib">
Inheriting from multiple extensions
You may use multiple ep-package statements, as in
<ep-package name="HTML::EP::Locale">
<ep-package name="HTML::EP::Session">
Your object will be blessed into a new class, that inherits from both.
However, note that the order is reversed: In the above example, your
object will be an instance of class HTML::EP::PACK2 and
HTML::EP::PACK2::ISA will be set to
qw(HTML::EP::Session HTML::EP::Locale)
CHANGES
This section describes user visible changes against previous versions.
For details and other modifications see the `ChangeLog' file, that is
part of the distribution.
epparse
epperl In previous versions it was not possible to include EP variables or
Perl code in attributes of EP commands, unless using a prefix
`epparse-' or `epperl-', as in
<ep-mail to=joe epparse-from="$cgi->mail$" subject=Hello>
This is no longer the case, because the package now autodetects
whether you are using such constructs. (At least it should. :-)
The obvious disadvantage is an incompatibility, but the new
version is much better readable and surprisingly even (much!)
faster, because only hash values are modified and not hash
structures.
TODO
Create an EP server that is accessible via a small C wrapper
Add a preprocessor, that creates Perl code as output.
AUTHOR AND COPYRIGHT
This module is
Copyright (C) 1998-1999 Jochen Wiedmann
Am Eisteich 9
72555 Metzingen
Germany
Phone: +49 7123 14887
Email:
[email protected]
All rights reserved.
You may distribute this module under the terms of either the GNU General
Public License or the Artistic License, as specified in the Perl README
file.
SEE ALSO
the DBI(3) manpage, the CGI(3) manpage, the HTML::Parser(3) manpage
