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NAME

ePerl - Embedded Perl 5 Language
 

VERSION

SYNOPSIS

eperl [-r] [-l] [-v] [-V]  

DESCRIPTION

Abstract

Introduction

  #!/path/to/perl
  print "foo bar\n";
  print "baz quux\n";
  for ($i = 0; $i < 10; $i++) { print "foo #${i}\n"; }
  print "foo bar\n";
  print "baz quux\n";

  #!/path/to/eperl
  foo bar
  baz quux
  <: for ($i = 0; $i < 10; $i++) { print "foo #${i}\n"; } :>
  foo bar
  baz quux

Intention

Due to the nature of such bristled code, ePerl is really the better attempt when the generated ASCII data contains really more static as dynamic data. Or in other words: Use ePerl if you want to keep the most of the generated ASCII data in plain format while just programming some bristled stuff. Do not use it when generating pure dynamic data. There it brings no advantage to the ordinary program code of a plain Perl script. So, the static part should be at least 60% or the advantage becomes a disadvantage.

ePerl in its origin was actually designed for an extreme situation: as a webserver scripting-language for on-the-fly HTML page generation. Here you have the typical case that usually 90% of the data consists of pure static HTML tags and plain ASCII while just the remaining 10% are programming constructs which dynamically generate more markup code. This is the reason why ePerl beside its standard Unix filtering runtime-mode also supports the CGI/1.1 and NPH-CGI/1.1 interfaces.  

Embedded Perl Syntax

1. Delimiters are always discarded.

Trivially to say, but should be mentioned at least once. The ePerl block delimiters are always discarded and are only necessary for ePerl to recognize the embedded Perl constructs. They are never passed to the final output.

2. Generated content has to go to STDOUT.

Although you can define subroutines, calculate some data, etc. inside ePerl blocks only data which is explicitly written to the STDOUT filehandle is expanded. In other words: When an ePerl block does not generate content on STDOUT, it is entirely replaced by an empty string in the final output. But when content is generated it is put at the point of the ePerl block in the final output. Usually contents is generated via pure print constructs which implicitly use STDOUT when no filehandle is given.

3. Generated content on STDERR always leads to an error.

Whenever content is generated on the STDERR filehandle, ePerl displays an error (including the STDERR content). Use this to exit on errors while passing errors from ePerl blocks to the calling environment.

4. Last semicolon.

Because of the following point 6 (see below) and the fact that most of the users don't have the internal ePerl block translations in mind, ePerl is smart about the last semicolon. Usually every ePerl block has to end with the semicolon of the last command.

   <: cmd; ...; cmd; :>

But when the last semicolon is missing it is automatically added by ePerl, i.e.

   <: cmd; ...; cmd :>

is also correct syntax. But sometimes it is necessary to force ePerl not to add the semicolon. Then you can add a ``_'' (underscore) as the last non-whitespace character in the block to force ePerl to leave the final semicolon. Use this for constructs like the following

   <: if (...) { _:>
   foo
   <: } else { _:>
   bar 
   <: } :>

where you want to spread a Perl directive over more ePerl blocks.

5. Shorthand for print-only blocks.

Because most of the time ePerl is used just to interpolate variables, e.g.

   <: print $VARIABLE; :>

it is useful to provide a shortcut for this kind of constructs. So ePerl provides a shortcut via the character `='. When it immediately (no whitespaces allowed here) follows the begin delimiter of an ePerl block a print statement is implicitly generated, i.e. the above block is equivalent to

   <:=$VARIABLE:>

Notice that the semicolon was also removed here, because it gets automatically added (see above).

6. Special EndOfLine discard command for ePerl blocks.

ePerl provides a special discard command named ``//'' which discards all data up-to and including the following newline character when directly followed an end block delimiter. Usually when you write

  foo
  <: $x = 1; :>
  quux

the result is

  foo
  
  quux

because ePerl always preserves code around ePerl blocks, even just newlines. But when you write

  foo
  <: $x = 1; :>//
  quux

the result is

  foo
  quux

because the ``//'' deleted all stuff to the end of the line, including the newline.

7. Restrictions in parsing.

Every program has its restrictions, ePerl too. Its handicap is that Perl is not only a rich language, it is a horrible one according to parsing its constructs. Perhaps you know the phrase ,,Only perl can parse Perl''. Think about it. The implication of this is that ePerl never tries to parse the ePerl blocks itself. It entirely relies on the Perl interpreter library, because it is the only instance which can do this without errors. But the problem is that ePerl at least has to recognize the begin and end positions of those ePerl blocks.

There are two ways: It can either look for the end delimiter while parsing but at least recognize quoted strings (where the end delimiter gets treated as pure data). Or it can just move forward to the next end delimiter and say that it have not occur inside Perl constructs. In ePerl 2.0 the second one was used, while in ePerl 2.1 the first one was taken because a lot of users wanted it this way while using bad end delimiters like ``>''. But actually the author has again revised its opinion and decided to finally use the second approach which is used since ePerl 2.2 now. Because while the first one allows more trivial delimiters (which itself is not a really good idea), it fails when constructs like ``m|"[^"]+"|'' etc. are used inside ePerl blocks. And it is easier to escape end delimiters inside Perl constructs (for instance via backslashes in quoted strings) than rewrite complex Perl constructs to use even number of quotes.

So, whenever your end delimiter also occurs inside Perl constructs you have to escape it in any way.

8. HTML entity conversion.

Because one of ePerl's usage is as a server-side scripting-language for HTML pages, there is a common problem in conjunction with HTML editors. They cannot know ePerl blocks, so when you enter those blocks inside the editors they usually encode some characters with the corresponding HTML entities. The problem is that this encoding leads to invalid Perl code. ePerl provides the option -C for decoding these entities which is automatically turned on in CGI modes. See description below under option -C for more details.

Runtime Modes

Stand-alone Unix filter mode

This is the default operation mode when used as a generation tool from the Unix shell or as a batch-processing tool from within other programs or scripts:

  $ eperl [options] - < inputfile > outputfile
  $ eperl [options] inputfile > outputfile
  $ eperl [options] -o outputfile - < inputfile
  $ eperl [options] -o outputfile inputfile

As you can see, ePerl can be used in any combination of STDIO and external files. Additionally there are two interesting variants of using this mode. First you can use ePerl in conjunction with the Unix Shebang magic technique to implicitly select it as the interpreter for your script similar to the way you are used to with the plain Perl interpreter:

  #!/path/to/eperl [options]
  foo
  <: print "bar"; :>
  quux

Second, you can use ePerl in conjunction with the Bourne-Shell Here Document technique from within you shell scripts:

  #!/bin/sh
  ...
  eperl [options] - <<EOS
  foo
  <: print "quux"; :>
  quux
  EOS
  ...

And finally you can use ePerl directly from within Perl programs by the use of the Parse::ePerl(3) package (assuming that you have installed this also; see file INSTALL inside the ePerl distribution for more details):

  #!/path/to/perl
  ...
  use Parse::ePerl;
  ...
  $script = <<EOT;
  foo
  <: print "quux"; :>
  quux
  EOT
  ...
  $result = Parse::ePerl::Expand({
      Script => $script,
      Result => \$result,
  });
  ...
  print $result;
  ...

See Parse::ePerl(3) for more details.

CGI/1.1 compliant interface mode

This is the runtime mode where ePerl uses the CGI/1.1 interface of a webserver when used as a Server-Side Scripting Language on the Web. ePerl enters this mode automatically when the CGI/1.1 environment variable PATH_TRANSLATED is set and its or the scripts filename does not begin with the NPH prefix ``nph-''. In this runtime mode it prefixes the resulting data with HTTP/1.0 (default) or HTTP/1.1 (if identified by the webserver) compliant response header lines.

ePerl also recognizes HTTP header lines at the beginning of the scripts generated data, i.e. for instance you can generate your own HTTP headers like

   <? $url = "..";
      print "Location: $url\n";
      print "URI: $url\n\n"; !>
   <html>
   ...

But notice that while you can output arbitrary headers, most webservers restrict the headers which are accepted via the CGI/1.1 interface. Usually you can provide only a few specific HTTP headers like Location or Status. If you need more control you have to use the NPH-CGI/1.1 interface mode.

Additionally ePerl provides a useful feature in this mode: It can switch its UID/GID to the owner of the script if it runs as a Unix SetUID program (see below under the Security manpage and the option ``u+s'' of chmod(1)).

There are two commonly known ways of using this CGI/1.1 interface mode on the Web. First, you can use it to explicitly transform plain HTML files into CGI/1.1 scripts via the Shebang technique (see above). For an Apache webserver just put the following line as the first line of the file:

  #!/path/to/eperl -mc

Then rename the script from file.html to file.cgi and set its execution bit via

  $ mv file.html file.cgi
  $ chmod a+rx file.cgi

Now make sure that Apache accepts file.cgi as a CGI program by enabling CGI support for the directory where file.cgi resides. For this add the line

  Options +ExecCGI

to the .htaccess file in this directory. Finally make sure that Apache really recognizes the extension .cgi. Perhaps you additionally have to add the following line to your httpd.conf file:

  AddHandler cgi-script .cgi

Now you can use file.cgi instead of file.html and make advantage of the achieved programming capability by bristling file.cgi with your Perl blocks (or the transformation into a CGI script would be useless).

Alternatively (or even additionally) a webmaster can enable ePerl support in a more seemless way by configuring ePerl as a real implicit server-side scripting language. This is done by assigning a MIME-type to the various valid ePerl file extensions and forcing all files with this MIME-type to be internally processed via the ePerl interpreter. You can accomplish this for Apache by adding the following to your httpd.conf file

  AddType      application/x-httpd-eperl  .phtml .eperl .epl
  Action       application/x-httpd-eperl  /internal/cgi/eperl
  ScriptAlias  /internal/cgi              /path/to/apache/cgi-bin

and creating a copy of the eperl program in your CGI-directory:

  $ cp -p /path/to/eperl /path/to/apache/cgi-bin/eperl

Now all files with the extensions .phtml, .eperl and .epl are automatically processed by the ePerl interpreter. There is no need for a Shebang line or any locally enabled CGI mode.

One final hint: When you want to test your scripts offline, just run them with forced CGI/1.1 mode from your shell. But make sure you prepare all environment variables your script depends on, e.g. QUERY_STRING or PATH_INFO.

  $ export QUERY_STRING="key1=value1&key2=value2"
  $ eperl -mc file.phtml

NPH-CGI/1.1 compliant interface mode

This runtime mode is a special variant of the CGI/1.1 interface mode, because most webservers (e.g. Apache) provide it for special purposes. It is known as Non-Parsed-Header (NPH) CGI/1.1 mode and is usually used by the webserver when the filename of the CGI program is prefixed with ``nph-''. In this mode the webserver does no processing on the HTTP response headers and no buffering of the resulting data, i.e. the CGI program actually has to provide a complete HTTP response itself. The advantage is that the program can generate arbitrary HTTP headers or MIME-encoded multi-block messages.

So, above we have renamed the file to file.cgi which restricted us a little bit. When we alternatively rename file.html to nph-file.cgi and force the NPH-CGI/1.1 interface mode via option -mn then this file becomes a NPH-CGI/1.1 compliant program under Apache and other webservers. Now our script can provide its own HTTP response (it need not, because when absent ePerl provides a default one for it).

  #!/path/to/bin/eperl -mn
  <? print "HTTP/1.0 200 Ok\n";
     print "X-MyHeader: Foo Bar Quux\n";
     print "Content-type: text/html\n\n";
  <html>
  ...

As you expect this can be also used with the implicit Server-Side Scripting Language technique. Put

  AddType      application/x-httpd-eperl  .phtml .eperl .epl
  Action       application/x-httpd-eperl  /internal/cgi/nph-eperl
  ScriptAlias  /internal/cgi              /path/to/apache/cgi-bin

into your httpd.conf and run the command

  $ cp -p /path/to/eperl /path/to/apache/cgi-bin/nph-eperl

from your shell. This is the preferred way of using ePerl as a Server-Side Scripting Language, because it provides most flexibility.

Security

  $ cp -p /path/to/eperl /path/to/apache/cgi-bin/eperl
  $ chown root /path/to/apache/cgi-bin/eperl
  $ chmod u+s  /path/to/apache/cgi-bin/eperl

  $ cp -p /path/to/eperl /path/to/apache/cgi-bin/nph-eperl
  $ chown root /path/to/apache/cgi-bin/nph-eperl
  $ chmod u+s  /path/to/apache/cgi-bin/nph-eperl

For those of us who decided that this feature is essential for them ePerl tries really hard to make it secure. The following steps have to be successfully passed before ePerl actually switches its UID/GID (in this order):

  1. The script has to match the following extensions:
     .html, .phtml, .ephtml, .epl, .pl, .cgi
  2. The UID of the calling process has to be a valid UID,
     i.e. it has to be found in the systems password file
  3. The UID of the calling process has to match the 
     following users: root, nobody
  4. The UID of the script owner has to be a valid UID,
     i.e. it has to be found in the systems password file
  5. The GID of the script group has to be a valid GID,
     i.e. it has to be found in the systems group file
  6. The script has to stay below or in the owners homedir

Also remember that ePerl always eliminates the effective UID/GID, independent of the runtime mode and independent if ePerl has switched to the UID/GID of the owner. For security reasons, the effective UID/GID is always destroyed before the script is executed.  

ePerl Preprocessor

#include path

This directive is an include directive which can be used to include really any stuff, but was actually designed to be used to include other ePerl source files. The path can be either a relative or absolute path for the local filesystem or a fully qualified HTTP URL.

In case of the absolute path the file is directly accessed on the filesystem, while the relative path is first searched in the current working directory and then in all directories specified via option -I. In the third case (HTTP URL) the file is retrieves via a HTTP/1.0 request on the network. Here HTTP redirects (response codes 301 and 302) are supported, too.

Notice: While ePerl strictly preserves the line numbers when translating the bristled ePerl format to plain Perl format, the ePerl preprocessor can't do this (because its a preprocessor which expands) for this directive. So, whenever you use #include, remember that line numbers in error messages are wrong.

Also notice one important security aspect: Because you can include any stuff as it is provided with this directive, use it only for stuff which is under your direct control. Don't use this directive to include foreign data, at least not from external webservers. For instance say you have a ePerl page with #include http://www.foreigner.com/nice-page.html and at the next request of this page your filesystem is lost! Why? Because the foreigner recognizes that you include his page and are using ePerl and just put a simple ``<? system("rm -rf /"); !>'' in his page. Think about it. NEVER USE #INCLUDE FOR ANY DATA WHICH IS NOT UNDER YOUR OWN CONTROL. Instead always use #sinclude for such situations.

#sinclude path

This is the secure variant of #include where after reading the data from path all ePerl begin and end delimiters are removed. So risky ePerl blocks lost their meaning and are converted to plain text. Always use this directive when you want to include data which is not under your own control.

#if expr, #elsif expr, #else, #endif

These implement a CPP-style #if-[#else-]#endif construct, but with a Perl semantic. While the other directives are real preprocessor commands which are evaluated at the preprocessing step, this construct is actually just transformed into a low-level ePerl construct, so it is not actually evaluated at the preprocessing step. It is just a handy shortcut for the following (where BD is the currently used begin delimiter and ED the end delimiter):

  ``#if expr''    ->  ``BD if (expr) { _ ED//''
  ``#elsif expr'' ->  ``BD } elsif (expr) { _ ED//''
  ``#else''       ->  ``BD } else { _ ED//''
  ``#endif''      ->  ``BD } _ ED//''

The advantage of this unusual aproach is that the if-condition really can be any valid Perl expression which provides maximum flexibility. The disadvantage is that you cannot use the if-construct to make real preprocessing decisions. As you can see, the design goal was just to provide a shorthand for the more complicated Perl constructs.

#c

This is the comment directive which just discards all data up to and including the newline character. Use this one to comment out any stuff, even other preprocessor directives.

Provided Functionality

The answers are: First, you can put really any Perl code into the ePerl blocks which are valid to the Perl interpreter ePerl was linked with. Second, ePerl does not provide any special functionality inside these ePerl blocks, because Perl is already sophisticated enough ;-)

The implication of this is: Because you can use any valid Perl code you can make use of all available Perl 5 modules, even those ones which use shared objects (because ePerl is a Perl interpreter, including DynaLoader support). So, browse to the Comprehensive Perl Archive Network (CPAN) via http://www.perl.com/perl/CPAN and grab your favorite packages which can make your life easier (both from within plain Perl scripts and ePerl scripts) and just use the construct ``use name;'' in any ePerl block to use them from within ePerl.

When using ePerl as a Server-Side-Scripting-Language I really recommend you to install at least the packages CGI.pm (currently vers. 2.36), HTML-Stream (1.40), libnet (1.0505) and libwww-perl (5.08). When you want to generate on-the-fly images as well, I recommend you to additionally install at least GD (1.14) and Image-Size (2.3). The ePerl interpreter in conjunction with these really sophisticated Perl 5 modules will provide you with maximum flexibility and functionality. In other words: Make use of maximum Software Leverage in the hackers world of Perl as great as possible.  

OPTIONS

-d name=value

Sets a Perl variable in the package main which can be referenced via $name or more explicitly via $main::name. The command

  eperl -d name=value ..
  
is actually equivalent to having

  <? $name = value; !>

at the beginning of inputfile. This option can occur more than once.

-D name=value

Sets a environment variable which can be referenced via $ENV{'variable'} inside the Perl blocks. The command

  eperl -D name=value ..
  
is actually equivalent to 

  export name=value; eperl ...

but the advantage of this option is that it doesn't manipulate the callers environment. This option can occur more than once.

-B begin_delimiter

Sets the Perl block begin delimiter string. Use this in conjunction with -E to set different delimiters when using ePerl as an offline HTML creation-language while still using it as an online HTML scripting-language. Default delimiters are <? and !> for CGI modes and <: and :> for stand-alone Unix filtering mode.

There are a lot of possible variations you could choose: ``<:'' and ``:>'' (the default ePerl stand-alone filtering mode delimiters), ``<?'' and ``!>'' (the default ePerl CGI interface mode delimiters), ``<script language='ePerl'>'' and ``</script>'' (standard HTML scripting language style), ``<script type="text/eperl">'' and ``</script>'' (forthcoming HTML3.2+ aka Cougar style), ``<eperl>'' and ``</eperl>'' (HTML-like style), ``<!--#eperl code=''' and ``' -->'' (NeoScript and SSI style) or even ``<?'' and ``>'' (PHP/FI style; but this no longer recommended because it can lead to parsing problems. Should be used only for backward compatibility to old ePerl versions 1.x).

The begin and end delimiters are searched case-insensitive.

-E end_delimiter

Sets the Perl block end delimiter string. See also option -B.

-i

Forces the begin and end delimiters to be searched case-insensitive. Use this when you are using delimiters like ``<ePerl>...</ePerl>'' or other more textual ones.

-m mode

This forces ePerl to act in a specific runtime mode. See above for a detailed description of the three possible modes: Stand-alone filter (mode=f, i.e. option -mf), CGI/1.1 interface mode (mode=c, i.e. option -mc) or the NPH-CGI/1.1 interface mode (mode=n, i.e. option -mn).

-o outputfile

Forces the output to be written to outputfile instead of STDOUT. Use this option when using ePerl as a filter. The outputfile ``-'' sets STDOUT as the output handle explicitly. Notice that this file is relative to the source file directory when the runtime mode is forced to CGI or NPH-CGI.

-k

Forces ePerl to keep the current working directory from where it was started. Per default ePerl will change to the directory where the file to be executed stays. This option is useful if you use ePerl as an offline filter on a temporary file.

-x

This sets debug mode where ePerl outputs the internally created Perl script to the console (/dev/tty) before executing it. Only for debugging problems with the inputfile conversion.

-I directory

Specify a directory which is both used for #include and #sinclude directives of the ePerl preprocessor and added to @INC under runtime. This option can occur more than once.

-P

Manually enables the special ePerl Preprocessor (see above). This option is enabled for all CGI modes automatically.

-C

This enables the HTML entity conversion for ePerl blocks. This option is automatically forced in CGI modes.

The solved problem here is the following: When you use ePerl as a Server-Side-Scripting-Language for HTML pages and you edit your ePerl source files via a HTML editor, the chance is high that your editor translates some entered characters to HTML entities, for instance ``<'' to ``&lt;''. This leads to invalid Perl code inside ePerl blocks, because the HTML editor has no knowledge about ePerl blocks. Using this option the ePerl parser automatically converts all entities found inside ePerl blocks back to plain characters, so the Perl interpreter again receives valid code blocks.

-L

This enables the line continuation character ``\'' (backslash) outside ePerl blocks. With this option you can spread oneline-data over more lines. But use with care: This option changes your data (outside ePerl blocks). Usually ePerl really pass through all surrounding data as raw data. With this option the newlines become new semantics.

-T

This enabled Perl's Tainting mode where the Perl interpreter takes special precautions called taint checks to prevent both obvious and subtle traps. See perlsec(1) for more details.

-w

This enables Warnings where the Perl interpreter produces some lovely diagnostics. See perldiag(1) for more details.

-c

This runs a pure syntax check which is similar to ``perl -c''.

-r

This prints the internal ePerl README file to the console.

-l

This prints the internal ePerl LICENSE file to the console.

-v

This prints ePerl version information to the console.

-V

Same as option -v but additionally shows the Perl compilation parameters.

ENVIRONMENT

Used Variables

PATH_TRANSLATED

This CGI/1.1 variable is used to determine the source file when ePerl operates as a NPH-CGI/1.1 program under the environment of a webserver.

Provided Variables

SCRIPT_SRC_PATH

The absolute pathname of the script. Use this when you want to directly access the script from within itself, for instance to do stat() and other calls.

SCRIPT_SRC_PATH_DIR

The directory part of SCRIPT_SRC_PATH. Use this one when you want to directly access other files residing in the same directory as the script, for instance to read config files, etc.

SCRIPT_SRC_PATH_FILE

The filename part of SCRIPT_SRC_PATH. Use this one when you need the name of the script, for instance for relative self-references through URLs.

SCRIPT_SRC_URL

The fully-qualified URL of the script. Use this when you need a URL for self-reference.

SCRIPT_SRC_URL_DIR

The directory part of SCRIPT_SRC_URL. Use this one when you want to directly access other files residing in the same directory as the script via the Web, for instance to reference images, etc.

SCRIPT_SRC_URL_FILE

The filename part of SCRIPT_SRC_URL. Use this one when you need the name of the script, for instance for relative self-references through URLs. Actually the same as SCRIPT_SRC_PATH_FILE, but provided for consistency.

SCRIPT_SRC_SIZE

The filesize of the script, in bytes.

SCRIPT_SRC_MODIFIED

The last modification time of the script, in seconds since 0 hours, 0 minutes, 0 seconds, January 1, 1970, Coordinated Universal Time.

SCRIPT_SRC_MODIFIED_CTIME

The last modification time of the script, in ctime(3) format (``WDAY MMM DD HH:MM:SS YYYY\n'').

SCRIPT_SRC_MODIFIED_ISOTIME

The last modification time of the script, in ISO format (``DD-MM-YYYY HH:MM'').

SCRIPT_SRC_OWNER

The username of the script owner.

VERSION_INTERPRETER

The ePerl identification string.

VERSION_LANGUAGE

The identification string of the used Perl interpreter library.

Provided Built-In Images

logo.gif

The standard ePerl logo. Please do not include this one on your website.

powered.gif

The ``powered by ePerl 2.2'' logo. Feel free to use this on your website.

AUTHOR

  Ralf S. Engelschall
  rse@engelschall.com
  www.engelschall.com

SEEALSO

Web-References:

  Perl:   perl(1),  http://www.perl.com/
  ePerl:  eperl(1), http://www.engelschall.com/sw/eperl/
  Apache: httpd(8), http://www.apache.org/

Index

NAME

VERSION

SYNOPSIS

DESCRIPTION

Abstract

Introduction

Intention

Embedded Perl Syntax

Runtime Modes

Security

ePerl Preprocessor

Provided Functionality

OPTIONS

ENVIRONMENT

Used Variables

Provided Variables

Provided Built-In Images

AUTHOR

SEEALSO

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