Provided by: libembperl-perl_2.5.0-17_amd64 
NAME
Embperl::Faq - How to embed Perl code in your HTML docs
CONTENTS
"Downloading, Compiling & Installing"
"Common Problems"
"Common Questions"
"Escaping & Unescaping"
"Debugging"
"Customizing"
"Optimizing & Fine Tuning"
"Additional Help"
Downloading, Compiling & Installing
For basics on downloading, compiling, and installing, please see the "INSTALLATION" in
INSTALL in the Embperl documentation. Please be sure to load Embperl at server startup -
if you do not, various problems may result. An exception to that rule is when you have
compiled mod_perl with USE_DSO. In this case you must not load Embperl at server statup,
neither via an use in your startup.pl file, nor via PerlModule from your httpd.conf.
Is there a binary distribution of Embperl for Unix?
No.
Is there a binary distribution of Embperl for Win32?
Win NT/95/98 binarys for Apache/perl/mod_perl/Embperl are available from
ftp://theoryx5.uwinnipeg.ca/pub/other/ . A european mirror is at
http://www.robert.cz/misc/ .
I want to run Embperl with mod_perl under Apache. In what order should I do the compiling?
First mod_perl and Apache, then Embperl.
I'm getting:
../apache_1.3.0/src/include/conf.h:916: regex.h: No such file or directory
Try compiling Embperl again, like this:
make DEFS=-DUSE_HSREGEX
I'm trying to build HTML::Embperl, and while running 'make' i get:
cc: Internal compiler error: program cc1 got fatal signal 11 make: *** [epmain.o] Error 1
GCC croaking with signal 11 frequently indicates hardware problems. See
http://www.bitwizard.nl/sig11/
I have a lot of errors in 'make test' from mod_perl when using Embperl
Try recompiling Perl and all modules -- this can sometimes make those annoying error
messages disappear!
How can I prevent 'make test' from running some of the tests?
For example, I don't allow CGI scripts, so 'make test' fails at CGI. How do I run just the
other tests?
Try:
$ make test TESTARGS="--help"
# and for just offline and mod_perl:
$ make test TESTARGS="-hoe"
Running 'make test' fails with an error message at loading of Embperl (even though mod_perl
compiled and tested cleanly!)
see "I get symbol ap_* undefined/cannot resolve ap_*"
I get symbol ap_* undefined/cannot resolve ap_*
This can happen when symbols in the Apache binary can not be found or are not being
resolved correctly.
Some OS do this (for instance bsdos), and it can also happen if your Apache binary is set
to strip symbol information out from binaries.
Try:
1.) make clean
2.) perl Makefile.PL
NOTE: answer _no_ to mod_perl support. (This is important!)
3.) make test
If that works, it means that your installation of Embperl is OK, but is having problems
resolving symbols with Apache.
Try rebuilding Apache and mod_perl from scratch, and make sure you do not strip symbols
out of either.
On some systems/linker you need to tell the linker explicitly to export such symbols. For
example FreeBSD linker needs the "-export-dynamic" option.
If you don't succeed with this approach, try statically linking Embperl to Apache/mod_perl
(please see the next question for step-by-step instructions on how to do this).
How can I build a statically-linked copy of Embperl with mod_perl support?
1.) go to your mod_perl directory, change to src/modules/perl and edit the Makefile so
that it contains the line
#STATIC_EXTS = Apache Apache::Constants HTML::Embperl
2.) add a definition for EPDIR and change the ONJ= line so that it looks like this:
EPDIR=/usr/msrc/embperl OBJS=$(PERLSRC:.c=.o) $(EPDIR)/Embperl.o $(EPDIR)/epmain.o
$(EPDIR)/epio.o (EP DIR)/epeval.o $(EPDIR)/epcmd.o $(EPDIR)/epchar.o $(EPDIR)/eputil.o
3.) go to the mod_perl directory and run
perl Makefile.PL
4.) go to the Embperl directory and do
make clean
perl Makefule.PL
make
(to compile in mod_perl support)
5.) go back to the mod_perl directory and remake Apache by typing
make
Now you have successfully built a httpd with statically-linked Embperl.
NOTE: If you want to stop here, you can skip to step 11. and run a 'make install' in
the Embperl directory to finish.
But if you want to run Embperl tests and/or if you want to be able to use Embperl in
offline or "vanilla" CGI mode, we need to continue:
6.) go back to the Embperl directory
7.) backup the file test/conf/config.pl
8.) now build Embperl again but _without_ mod_perl support
make clean
perl Makefile.PL
make
9.) restore your saved config.pl to test/conf/config.pl
(without this step, only the offline mode would be tested)
10.) run 'make test' for Embperl
11.) do 'make install' for Embperl
NOTE: You should do it in this order, or it may not work.
NOTE: It seems to be necessary to load Embperl at server startup, either by PerlModule or
in a PerlScript. See next question on how to do this.
How do I load Embperl at server startup?
You can load Embperl at server startup by PerlModule or in a startup.pl:
1.) edit your srm.conf file to read:
PerlModule HTML::Embperl
2.) edit your startup.pl file to read:
use HTML::Embperl
NOTE 1: Either of these approaches can often 'fix' SIGSEVs in any mod_perl handler, not
just Embperl.
NOTE 2: When mod_perl is compiled as loadable module (i.e. with USE_DSO) you must not load
Embperl at server startup time!
make test fails with a SIGxxxx, how can I obtain a stack backtrace from gdb?
The eaiest way is
make install -> if Embperl is installed, it's easier
gdb perl -> start the debugger with perl binary
set args test.pl -> set the arguments for perl
r -> start the program
-> Here you should receive the signal
share -> makes sure all symbols are really loaded
bt -> show the backtrace
To get some more information it would be a good idea to compile Embperl with debugging
information enabled. Therefore do
How do I build Embperl with debugging information
edit the Makefile
search for the line starting with 'CC = ' add the -g switch to the end of the line
search for the line starting with 'LDDFLAGS = ' add the -g switch to the end of the line
type make to build Embperl with debugging infomation
now start the gdb as described before.
make test fails with SIGXFSZ
This may occur when the filesize limit for the account, either test is running as or the
test httpd, is too small. Embperl make test generates a really large logfile! Yu must
increase the filesize limit for that accounts.
Embperl on SCO Unix
>From Red Plait
My OS is SCO Unix 3.2v4.2, Apache 1.3.4, perl 5.004_4, mod_perl 1.18 and Embperl-1.1.1
I done following:
1) I made HTML-Embperl-1.1.1 with no mod_perl support ( when I builded it with mod_perl
1.18 I can`t link it because it don`t finds ap_XXX functions. When I manually insert
src/main/libmain.a from Apache 1.3.4 I got message "Symbol main is multiple defined in
/src/main/libmain.a. and perlmain.o" ). Then I "make test" - all tests was O`k. After
this I "make clean", "perl Makefile.pl" with mod_perl support and "make install"
2) I installed mod_perl and "perl Makefile.PL", then "make"
3) because I have`nt dynamical loading ( very old and buggy OS ) I had to manually change
src/modules/perl/perlxsi.c to insert bootstraps function`s and it`s invocations and
also /src/Makefile to manually insert libXXX.a libraries
In access.conf I insert code:
PerlModule HTML::Embperl
<Directory /my_dir>
SetHandler perl-script
PerlHandler HTML::Embperl::handler
</Directory>
Embperl and mod_perl on AIX
You need at least mod_perl 1.22. For mod_perl 1.22 and higher Embperl should compile out
of the box on AIX. If you run into problems with undefined symbols (like "ap_*") make sure
you have the newest mod_perl version (as of this writing this is mod_perl 1.24_01).
Embperl does not write to the logfile, because of missing permissions of the user Apache runs
as.
The apache server is started as root, then set the effective uid to user "www", who can
then write to the embperl logfile (owned by root) file handle that is passed along.
However, if this log file handle is later accidentally closed, then reopen, the www user
would have problem writing to it?
The reopen is only done when the logfile name changes. As log as you don't change the name
on the logfile, the logfile will stay open.
The problem (in this case) is, that Embperl init function ,(Init in epmain.c) calls
OpenLog will an second argument of zero. Which will only save the filename. The log will
actually opened on the first write to it (or at the start of the first request). At this
time your Apache has already switch to user www. This is done to allow one to change the
logfile name before a request, but after the init is already called (which is done when
you or Apache "use" the module)
The current solutions is to write something to the log, before Apache changes it's user
(i.e. in the startup.pl)
Is it possible to install EmbPerl into a private directory on my Unix/Linux Internet Service
Provider account of which I have no root privilege?
Like any other Perl module it can. Read "perldoc ExtUtils::MakeMaker", to see which
parameters are needed for Makefile.PL to change the installation directory. Additionally,
you have to change the @INC path to contain your private directory and possibly paths to
other object files.
Here are the brief details:
Requirements:
• At least Perl 5.004_04
• cc or gcc (your isp must give you access to the gcc compiler)
• URI
• MIME::Base64
• HTML::Parser
• HTML::HeadParser
• Digest::MD5
• libnet
• libwww
• File::Spec (I believe you may have to install this too if you are using Perl 5.004_04
as it may not be a standard module)
Direction:
• Get your copy of EmbPerl (HTML-Embperl-x.x.tar.gz)
• % tar -xvzf HTML-Embperl-x.x.tar.gz
• % cd HTML-Embperl-x.x
• % perl Makefile.PL PREFIX=/to/your/private/dir
• % make
• % make test
• % make install
Replace /to/your/private/dir with the path to the directory you want the module to be
placed in. Now preface your CGI scripts with something like this:
[Alternative 1]
#!/usr/bin/perl -wT
use CGI::Carp qw( fatalsToBrowser ); #recommend using this to report errors on die or warn to browser
use lib '/to/your/private/dir/lib'; #for FILE::Spec
use lib '/to/your/private/dir/'; #to find Embperl
use lib '/to/your/private/dir/i386-linux/auto/HTML/Embperl'; #to find Embperl compiled stuff
#if for some very weird reason the above 'use lib' pragma directive doesn't work, see Alternative 2
use HTML::Embperl;
#your code below ...
[Alternative 2]
#!/usr/bin/perl -wT
use CGI::Carp qw( fatalsToBrowser ); #recommend using this to report errors on die or warn to browser
BEGIN {
unshift @INC, '/to/your/private/dir/lib'; #for FILE::Spec
unshift @INC, '/to/your/private/dir/'; #to find Embperl
unshift @INC, '/to/your/private/dir/i386-linux/auto/HTML/Embperl'; #to find Embperl compiled stuff
}
use HTML::Embperl;
#your code below ...
When you make test, you may encounter superfluous warnings, you may want to change the
test.pl that ships with EmbPerl from
BEGIN
{
$fatal = 1 ;
to
BEGIN
{
unshift @INC, '/to/your/private/dir/lib';
$fatal = 1 ;
...
because the test.pl may not be able to find FILE::Spec if you have it installed on a
private directory for Perl 5.004_04.
Do something similar to the important file embpcgi.pl as you do for all your CGI scripts,
like modifying the @INC as shown above, to allow perl to find in particular the EmbPerl
shared obj files...
And when you invoke your CGI scripts like so,
http://www.yourdomain.com/cgi-bin/embpcgi.pl/templateFiles/myNifty.epl
the script should work.
Common Problems
The most common problems of all involve Escaping and Unescaping. They are so common, that
an entire section on "Escaping & Unescaping" is devoted to them.
When I use a module inside an Embperl page, it behaves weird when the source changes.
Nothing weird here. Everything is well defined. Just let us try to understand how Perl,
mod_perl and Embperl works together:
"perldoc -f use" tells us:
Imports some semantics into the current package from the named module,
generally by aliasing certain subroutine or variable names into your
package. It is exactly equivalent to
BEGIN { require Module; import Module LIST; }
except that Module must be a bareword.
So what's important here for us is, that "use" executes a "require" and this is always
done before any other code is executed.
"perldoc -f require" says (among other things):
..., demands that a library file be included if it hasn't already
been included.
and
Note that the file will not be included twice under the same specified
name.
So now we know (or should know) that mod_perl starts the Perl interpreter once when Apache
is started and the Perl interpreter is only terminated when Apache is terminated. Out of
these two things follows, that a module that is loaded via "use" or "require" is only
loaded once and will never be reloaded, regardless if the source changes or not.
So far this is just standard Perl. Things get a little bit more difficult when running
under mod_perl (only Unix), because Apache forks a set of child processes as necessary and
from the moment they are forked, they run on their own and don't know of each other. So if
a module is loaded at server startup time (before the fork), it is loaded in all children
(this can be used to save memory, because the code will actually only reside once in
memory), but when the modul is loaded inside the child and the source changes, it could be
happen, that one child has loaded an ealier version and another child has loaded a later
version of that module, depending on the time the module is actualy loaded by the child.
That explains, why sometimes it works and sometimes it doesn't, simply because different
children has loaded different versions of the same module and when you reload your page
you hit different children of Apache!
Now there is one point that is special to Embperl to add. Since Embperl compiles every
page in a different namespace, a module that doesn't contains a "package foo" statement is
compiled in the namespace of the page where it is first loaded. Because Perl will not
load the module a second time, every other page will not see subs and vars that are
defined in the loaded module. This could be simply avoided by giving every module that
should be loaded via "use"/"require" an explicit namespace via the package statement.
So what can we do?
• If a module change, simply restart Apache. That's works always.
• Use Apache::StatInc. This will do a stat on every loaded module and compare the
modification time. If the source has changed the module is reloaded. This works most
times (but not all modules can be cleanly reloaded) and as the number of loaded
modules increase, your sever will slow down, because of the stat it has to do for
every module.
• Use "do" instead of "require". "do" will execute your file every time it is used. This
also adds overhead, but this may be accpetable for small files or in a debugging
environment. (NOTE: Be sure to check $@ after a "do", because do works like "eval")
Why doesn't the following line work?
[+ $var . "<b>". $foo . "</b>". $bar +]
See what we mean? This is an Escaping & Unescaping problem for sure. You need to escape
<b> as ' <b> ' and you probably also need to read the section on "Escaping &
Unescaping"...
I'm getting: "Glob not terminated at ..."
This might be a problem with "Escaping & Unescaping" as well.
My HTML is getting stripped out.
Sounds like a problem with Escaping & Unescaping again!
Unless, of course, you have already read the section on Escaping & Unescaping, and it is
still happening... Like if you are using optRawInput and your HTML is _still_ being
stripped out...
I _am_ using optRawInput, and my HTML _is_ still being stripped out!
Aha! Well that's different! Never mind..
It can be easy to accidentally set optRawInput too late in your code...
Try setting it in an extra Perl block ( [- $optRawInput = 1 -] ) earlier in the code, or
in the server config, and see if that doesn't solve the problem... (optRawInput must be
set before the block that uses it begins, as the block which uses it shouldn't be
translated).
Help! I got a SIGSEGV! Ack!
If Embperl is not compiled at server startup, it can cause error messages, SEGfaults, core
dumps, buffer overflow, etc - especially if you are using another module inside an Embperl
page. As far as anyone can tell, this seems to be a Perl/mod_perl problem - but maybe not.
If you have any ideas, let me know.
To see the steps for loading Embperl at server startup, please see the section
"Downloading, Compiling & Installing".
NOTE: When mod_perl is compiled with USE_DSO it behaves vice versa and you may get
SIGSEGVs when Embper is loaded at server startup time.
I am having troubles with using Embperl in combination with Apache::Include inside a
Apache::Registry script.
This is a known problem, but it is a problem with mod_perl rather than with Embperl. It
looks like mod_perl clears the request_rec after the first subrequest, so that it later
doesn't know which subrequest was intended (unless it's explicitly specified). Try using:
Apache::Include->virtual("test.epl", $r);
(instead of just Apache::Include->virtual("test.epl"); where $r is the apache request rec)
I can't get PerlSendHeader to work under Embperl?
You don't need PerlSendHeader when using Embperl - Embperl always sends its own httpd
header.
But how do I customize the header that Embperl is sending?
You'll find the answer to this and many other header issues in the "Common Questions"
section.
I can't figure out how to split a 'while' statement across two [- -] segments
That isn't surprising, as you cannot split Perl statements across multiple [- -] blocks in
Embperl :) You need to use a metacommand for that. The [$while$] metacommand comes to
mind... :)
For a list of all possible metacommands, see the section on Meta-Commands in the Embperl
documentation.
[$ while $st -> fetch $]
#some html or other Embperl blocks goes here
[$ endwhile $]
Newer Embperl versions (1.2b3 and above) supports the [* *] which can be used for such
purposes.
[* while ($st -> fetch) { *]
#some html or other Embperl blocks goes here
[* } *]
While the later can use all Perl control structures, the first seems to me more readable
and is better debugable, because Embperl controls the execution of the control structure
it can do a quite better job in debug logging.
My HTML tags like '<' '>' and '"' are being translated to <, > !!!
Hey! Not you again!? I thought we already sent you to the "Escaping & Unescaping" section
of the FAQ?!?! ;)
Netscape asks to reload the document
If you have something like this in your source, it may be the problem:
<META HTTP-EQUIV="content-type" CONTENT="text/html;charset=iso-8859-1">
Netscape seems to have a problem in such cases, because the http header is only content-
type text/html, while the META HTTP-EQUIV has an additional charset specified. If you turn
optEarlyHttpHeader off, Embperl will automatically set the http header to be the same as
the META HTTP-EQUIV.
I get "Stack underflow"
The problem often occurs, when you have a <table> tag in one file and a </table> tag in
another file and you both include them in a main page (e.g. as header and footer). There
are two workarounds for this problem:
1. Set optDisableTableScan
This will avoid that Embperl takes any action on tables. You can disable/enable this
(also multiple times) inside the page with
[- $optDisableTableScan = 1 -]
If you put this at the top of your header/footer which you include with Execute, then
the main page will still process dynamic tables.
2. Add a <table> as comment
Add the following to the top of the footer document:
<!-- <table><tr><td> -->
This will work also, because Embperl (1.x) will not scan for html comments
Common Questions
The most common questions of all deal with "Escaping & Unescaping" - they are so common
that the whole next section is devoted to them. Less common questions are addressed here:
How can I get my HTML files to be converted into Perl code which, as a whole, could then be
compiled as function so that I could, for instance, fetch Perl docs from the Formatter
table and compile them the way AUTOLOAD does.
Embperl cannot covert your HTML into one piece of Perl-code, but you can wrap the call to
Execute into a Perl function and let AUTOLOAD call it.
I have an HTML page which is dynamically generated at runtime and should be post-processed by
Embperl. How can I do this?
1.) Generate the page within a normal CGI/Apache::Registry script and put the result into
a scalar - then you can call HTML::Embperl::Execute to post-process your document. Execute
can either send the document to the browser or put it into another scalar for further
processing.
2.) Use EMBPERL_INPUT_FUNC (1.1b1 and above). With this configuration directive, you can
specify a custom input function which reads the HTML source from the disk or even from a
database. Embperl also provides the function ProxyInput, which allows you to get input
from another web server altogether.
3.) Look at the module Apache::EmbperlChain, which is able to chain multiple modules,
including Embperl, together.
How can I customise the header that Embperl is sending?
You can write it as
<meta http-equiv="Content-Type" content="text/html">
(Embperl will automatically insert all meta http-equiv tags into the http header)
or use %http_headers_out
[- $http_headers_out{'Content-Type'} = 'text/html' -]
or (only when running under mod_perl) you can use
[- $req_rec -> content_type ('text/html') -]
Can I use Embperl to send cookies?
Yes. Embperl sends its own headers, so all you have to do to send cookies is to remember
to print an additional header.
Example Code:
1.) in documents, add
<META HTTP-EQUIV="Set-Cookie" CONTENT="[+ $cookie +] = [+ $value +]">
2.) or use %http_headers_out
[- $http_headers_out{'Set-Cookie'} = "$cookie=$value" -]
3.) or - using mod_perl's functionality - use
[- $req_rec -> header_out("Set-Cookie" => "$cookie=$value"); -]
NOTE: You make also take a look at Embperls (1.2b2 and above) ability to handle sessions
for you inside the %udat and %mdat hashes.
Can I do a Redirect with Embperl?
The following way works with mod_perl and as cgi:
[- $http_headers_out{'Location'} = "http://www.ecos.de/embperl/" -]
the status of the request will automatically set to 301.
or use the mod_perl function Apache::header_out.
Example Code:
[-
use Apache;
use Apache::Constants qw(REDIRECT);
$req_rec->header_out("Location" => "http://$ENV{HTTP_HOST}/specials/");
$req_rec->status(REDIRECT);
-]
If there is nothing more to do on this page, you may call "exit" directly after setting
the status.
Can I serve random GIFs with Embperl? (Will Lincoln Stein's GD.pm module work with Embperl??)
As always, there is more than one way to do this - especially as this is more of a
question of how you are coding your HTML than how you are coding your Embperl.
Here are some ideas:
1.) You could include an IMG tag which points to your cgi-bin, where a regular CGI script
serves the graphics.
2.) You could be running Apache::Registry, which can generate on-the-fly GIFs using GD.
(This is just the same as if you were including the GD image from a static page or from
another CGI script, but it allows all of the appropriate logic to live in a single
document, which might be appropriate for some Embperl users).
If you think of another way, or come up with some sample code, I'd love to hear from you,
so that I could add it to the FAQ...
Can I use Embperl as a template for forms? Can I make form values persist (like with "vanilla"
CGI)? Does Embperl rewrite my template file so that parameters of things like
INPUT/TEXTAREA/SELECT persist?
Yes. Your page design staff should just be able to say <input name="foo"> and let the
default attributes of "foo" be defined elsewhere - for instance in a settings file. In
this case, %fdat should be pre-set with your default values. Setting $fdat{foo} = "abc"
will cause Embperl to change the above code to <input name="foo" value="abc">.
Does Embperl automatically add HIDDEN fields?
The [$hidden$] metacommand creates hidden fields for every entry in %fdat which was not
used by any other input tag so far.
You can also try something like this:
[-
$fdat{foo} = "abc" ;
$fdat{bar} = "xyz" ;
-]
<input name="foo">
[$hidden$]
and Embperl will create:
<input name="foo" value="abc">
<input type=hidden name="bar" value="xyz">
For a list of all possible metacommands, see the section on Meta-Commands in the Embperl
documentation.
What about security? Is Embperl Secure?
Just like anything else, Embperl is as secure as you make it. Embperl incorporates
Safe.pm, which will make it impossible to accidentally access other Packages - it also
permits the Administrator to disable Perl opcodes, etc.
For more on security, please see "(Safe-)Namespaces and opcode restrictions" in Embperl in
the Embperl documentation.
Is there any plan to make Embperl an Object so someone could subclass it and override certain
of its methods? (For example, I'd like to let it parse the file for me, but then let me
control the manipulation of the form tags.)
Embperl is going to be an Object from version 1.2b1. This, among other things, make it re-
entrant, so that you will be able to call Execute from within an Embperl page. It will
also mean that Embperl will come with hooks, which will allow you to alter or change the
way Embperl processes code. The details have not all been worked out yet, but I'm working
on it... :)
Are Embperl routines currently pre-compiled or even cached, or are only fragments cached?
All embedded Perl code is compiled the first time it is executed and cached for later use.
The second time the code is executed, only the precompiled p-code is called.
Every code block is compiled as a single subroutine. The HTML text between the Perl block
is still read from the file.
Why are Perl blocks broken up into single subroutines?
1.) It makes it easier to process the HTML tags between the Perl blocks - this gives you
more control over what's happening
2.) If you compiled _everything_ to Perl, you would hold all of the HTML text in memory,
and your Apache child processes would grow and grow... But often-accessed documents are
still held in memory by your os disk cache, which is much more memory-efficient.
3.) There is only so far that you can go with precompiling until you reach the point of
diminishing returns. My guess is that converting dynamic tables and other HTML processing
to Perl at this point in Embperl's development would actually slow down operation.
Can I pass QUERY_STRING information to an HTML::Embperl::Execute call?
With Embperl 1.0 and higher, you can do this. QUERY_STRING is set as $ENV{QUERY_STRING} by
default. Alternatively, you can use the fdat parameter to pass values to %fdat.
How to include other files into Embperl pages?
I am using embedded Perl on my site and am curious if I can use it for server side
includes. I want to embed the contents of file x.html into file y.html such that whenever
I change x.html, displaying y.html will also reflect this change. How do I do it using
embedded perl?
You need Embperl 1.2b4 or above. Then you can say inside of y.html:
[- Execute ('x.html') -]
EmbPerl iteration without indexing
I have a rather large table in a database which I'd like to display using EmbPerl. All of
the examples show a process of fetching all the data first, then iterating through it
using $row and $col, like this:
[-
$sth = $dbh -> prepare ("select * from $comptbl order by SubSystem");
$sth -> execute;
$dref = $sth -> fetchall_arrayref;
-]
<TABLE>
... $dref -> [$row][0] ...
</TABLE>
I'd prefer to fetch the data one row at a time, how can I do this?
For solution 1 you may write
<table>
[$while $rref = $sth -> fetch $]
<tr>....</tr>
[$endwhile$]
</table>
Solution 2 should work like this
<table>
<tr> [- $dummy = $row ; $rref = $sth -> fetch -]
....
</tr>
</table>
The table ends when the expression where $row is used in some way returns <undef>. So also
there is no releation between $row and the fetch, both conditions are met.
How to display arrays with undef values in it?
I'm doing a search on a table where some of the columns have NULL and non-NULL values.
DBIx::Recordset has no problem reading this values The problem is that I then tried to
print these values out in a table using Embperl's table feature, like this.
<TABLE>
<TR>
<TD>$set[$row]{column_name1}</TD>
<TD>$set[$row]{column_nameN}</TD>
</TR>
The problem is that I got 5 rows instead of the 15 that I was expected. I
have been trying all kinds of tweaks to the arguments to the Search
function and getting nowwhere, until I re-read the Embperl docs. Embperl
will not print out a table row if one of the columns has an
expression that
is undefined. This is a problem since DBIx::Recordset (and DBI)
natually uses undef to represent a NULL value for a column. So I made a
slight modification to my embperl code.
<TABLE>
<TR>
<TD>defined($set[$row]{column_name1}) ? $set[$row]{column_name1} :
"UNDEF"</TD>
. . .
<TD>$set[$row]{column_nameN} ? $set[$row]{column_nameN} : "UNDEF"</TD>
</TR>
Now all 15 rows appear as expected, with "UNDEF" representing the NULL values in the
database.
Another way top solve you problem may be:
<TABLE>
<TR>
[- $r = $set[$row] -]
<TD> [+ $r -> {column_name1} +] </TD>
. . .
<TD> [+ $r -> {column_nameN} +] </TD>
</TR>
This will only refer one time to $row and the expression is defined, as long as the row
could be fetched from the db. All NULL fields will be displayed as empty table cells.
Escaping & Unescaping
Escaping & Unescaping Input
By default, Embperl removes all HTML tags from the Perl source. It does this because many
high-end WYSIWYG HTML Editors (like MS Front Page) insert HTML tags like <FONT> and
<COLOR> in rather random places (like in the middle of your Perl code). This Embperl
feature keeps things like
[- $var = 1; <br>
$foo = 2 -]
permissible, so that you can enter Perl code while you mark up pages in an editor, all at
once. In this example, Embperl would remove the unnecessary <br> tag and, therefore, make
Perl happy. And if Perl is happy, we are all happy.
It is not difficult to change this behavior, if you are the kind of person who codes HTML
in an ascii editor (like vi or emacs).
If you use a high-level HTML editor, you shouldn't have any problems with input escaping,
because the editor will, for example, write a '<' as '<' in the HTML code. Embperl
translates this back to '<' and therefore it knows that this wasn't an HTML tag which
should be removed.
Problems with input escaping only occur if you use an ascii editor. Then you will need to
escape input (see the next section for details on how to do this).
To see the exact steps taken by Embperl to process a Perl-laden document, please see the
section Inside Embperl in the Embperl documentation.
Ways To Escape Input:
1. Escape it -> \<H1>
NOTE: Inside double quotes you will need to use \\ (double backslash), since Perl will
remove the first Escape itself.
Example: In most cases '\<tr>' but inside double-quotes "\\<tr>"
2. Turn off Escaping for all input by setting the optRawInput in EMBPERL_OPTIONS
3. Learn to avoid using HTML tags inside Perl code. Once you get the hang of it, you'll
love it.
Here is one example of how to do it:
[- $output = "<bold>Hello world</bold>" -]
[+ $output +]
write
[- $output = "Hello world<bold>" -]
this outputs
Hello world
or
<bold>[+ $output +]</bold>
this outputs
<bold>Hello world</bold>
And here is another example of how to do it:
[-
@a = ('a', 'b', 'c') ;
foreach $i (0..2)
{
$output. = "<tr><td>Row $a[$i]</td></tr>" ;
}
-]
<table>
[+ $output +]
</table>
The output here would be:
<table>Row aRow bRow c</table>
The Embperl version is
[-
@a = ('a', 'b', 'c') ;
-]
<table>
<tr><td>Row [+ $a[$row] +]</td></tr>" ;
</table>
The output will be
<table>
<tr><td>Row a</td></tr>" ;
<tr><td>Row b</td></tr>" ;
<tr><td>Row c</td></tr>" ;
</table>
And another: This elegant solution shows you how to take advantage of Embperl's ability to
create dynamic tables:
[-
use DBI;
my $dbh =
DBI->connect("DBI:mysql:database:localhost","Username","Password") ||
die($!);
$hstmt = $dbh->prepare("select ID, Heading from Shops order by Heading");
$hstmt->execute();
$dat = $hstmt->fetchall_arrayref() ;
$hstmt->finish();
$dbh->disconnect();
-]
<table border=1>
<tr><td>[+ $$dat[$row][$col] +]</td></tr>
</table>
This HTML code will then display the contents of the whole array.
Escaping & Unescaping Output
Embperl will also escape the output - so <H1> will be translated to <H1>
To see the exact steps taken by Embperl to process a Perl-laden document, please see
Inside Embperl in the Embperl documentation.
Ways To Escape Output:
1.) Escape it -> \\<H1>
(You need a double backslash \\, because
the first one is removed by Perl and the second by Embperl.
2.) set $escmode = 0 -> [- $escmode = 0 ; -]
3.) set SetEnv EMBPERL_ESCMODE 0 in your srm.conf
Debugging
I am having a hard time debugging Embperl code
Have you, umm, checked the error log? ;)
Have you tried setting debug flags higher by resetting EMBPERL_DEBUG in the server config
files? (And still higher? :)
dbgMem isn't usually very useful as it always outputs a lot of allocation. dbgFlushLog
and dbgFlushOutput should be used if (and only if) you are debugging SIGSEGVs.
For easy debugging, you can tell Embperl to display a link at the top of each page to your
log file. Then every error displayed in an error page is a link to the corresponding
position in the logfile, so you can easily find the place where something is going wrong
For more on using HTML links to the Embperl error log, see "EMBPERL_DEBUG" in Embperl in
the Embperldocs.
Embperl is running slow.
There are some debugging settings which may cause Embperl to drastically slow down. If you
are done with debugging, set debugging bits back to normal.
Also, using dbgFlushLog and dbgFlushOutput will make execution much slower. These are only
intended for debugging SIGSEGVs.
Never set all debugging bits!
How can I improve Embperl's performance?
1.) Load Embperl at server startup. This will cause UNIX systems to only allocate memory
once, and not for each child process. This reduces memory use, especially the need to swap
additional memory.
2.) Disable all unneeded debugging flags. You should never set dbgFlushLog dbgFlushOutput,
dbgMem and dbgEvalNoCache in a production environment.
3.) You may also want to take a look at the available options you can set via
EMBPERL_OPTIONS. For example optDisableChdir, will speed up processing because it avoid
the change directory before every request.
Customizing
How can I fiddle with the default values? How can I override or alter this or that behavior?
Usually, defaults are set in a way that is likely to make most sense for a majority of
users. As of version 1.0, Embperl allows much more flexibility in tweaking your own
default values than before. Take a look at EMBERPL_OPTIONS.
I'd like to (temporarily) disable some of Embperl's features. What can be customized?
1.) Use optDisableHtmlScan to disable processing of html tags. If this is set, Embperl
will only pay attention to these types of constructs:
[+/-/!/$ .... $/!/-/+]
2.) optDisableTableScan, optDisableInputScan and optDisableMetaScan can be used to disable
individual parts of HTML processing.
You may set these flags in your server config, or at runtime:
[+ $optDisableHtmlScan = 1 +]
<table> foo </table>
[+ $optDisableHtmlScan = 0 +]
How can I disable auto-tables?
Set optDisableTableScan in EMBPERL_OPTIONS
How can I change predefined values like $escmode from my Toolbox module?
$HTML::Embperl::escmode = 0 ;
Predefined values in Embperl are simply aliases for $HTML::Embperl::foo (for instance,
$escmode is an alias for $HTML::Embperl::escmode)
How can I customize the header that Embperl is sending?
You'll find the answer to this and many other header issues in the "Common Questions"
section.
How can I use a different character set? ASCII values over 128 are showing up as ? (question
marks)!
This is caused by the translation of characters to HTML escapes. Embperl translates them
to escapes which are then sometimes not understood by the browser, which may display a "?"
instead, because it is using the wrong character set.
If you want to use the escaping features of Embperl in this case, you have to adapt the
file "epchar.c" to your character set.
The distribution contain already an "epchar.c.iso-latin-2" from Jiri Novak which is an
replacement for epchar.c for the iso-8859-2 (iso-latin-2) character set. If you want to
use iso-latin-2, simply renmae "epchar.c.iso-latin-2" to "epchar.c". There is also an
file "epchar.c.min" from Sangmook Yi, which leaves all chars above 128 untouched, which is
especially useful for two byte charsets.
This file contains three tables:
Char2Html [] Convert characters to html escape
Char2Url [] Convert characters to url escapes (do not change this one!!)
Html2Char [] Convert html escapes to characters
You need to change the first and the last tables. Do not change the second table!!
Please make sure Char2Html contains one entry (and only one entry) for each of the 256
ascii codes (with none left undefined) in the right order, and that Html2Char is sorted by
html escape.
If somebody generates new tables for national character sets, please send a copy to the
author, so it can be included it in future versions of Embperl.
Optimizing & Fine-Tuning
How can I be sure that Embperl is re-compiling my page template (and the Perl blocks contained
in it) only when needed, and not each time?
As long as your input file's time stamp stays the same, Embperl will only compile the
script the first time it's called. When you use the Execute function, Embperl will
recompile the script only if the input file and mtime paramenters have changed since the
last time the script was called.
You can verfiy this by setting dbgDefEval. Now, every time a Perl block is compiled,
Embperl logs a line starting with DEF:. You will see this line only on the first request.
The cached Perl blocks are stored as a set of subroutines in the namespace of the
document. (HTML::Embperl::DOC::_<n> is the default) Look at the logfile to see the actual
name.
How can I pre-compile pages, so that each httpd child doesn't have to have its own separate
copies of the pre-compiled pages?
To pre-compile pages, just call Execute once for every file at server startup in your
startup.pl file.
In what namespace does Embperl store pre-compiled data?
The cached Perl blocks are stored as a set of subroutines in the namespace of the
document. (HTML::Embperl::DOC::_<n> for default) Look at the logfile to see the actual
name.
I have both Embperl and ordinary Perl processes running. The docs say that Embperl uses a
CGI.pm instance in its own internal processing, but they don't say how to control it. How
can I get Embperl to use *my* CGI.pm object instead of creating its own?
Embperl only creates a CGI objects to process multipart form data (from fileupload). In
all other cases Embperl doesn't use CGI.pm. There is no way to change this behaviour, or
access the internal CGI object in case of file-uploads.
Additional Help
Where can I get more help?
You can get free support on the mod_perl mailing list. If you need commercial support
(with a guarantee for response time or a solution) for Embperl, or if you want a web site
where you can run your Embperl/mod_perl scripts without setting up your own web server,
please send email to info@ecos.de.
Please also see the section "Support" in Embperl in the Embperl documentation.
SEE ALSO
some links here
AUTHOR
Gerald Richter <richter at embperl dot org>
Edited by Nora Mikes <nora@radio.cz>