FM / pod

/usr/share/perl5/pod

Name	Size	Mode	Actions
a2p.pod	6107	0644	edit dl rm
perl.pod	15748	0644	edit dl rm
perl56delta.pod	107184	0644	edit dl rm
perl58delta.pod	114908	0644	edit dl rm
perl561delta.pod	124697	0644	edit dl rm
perl570delta.pod	21655	0644	edit dl rm
perl571delta.pod	30382	0644	edit dl rm
perl572delta.pod	25551	0644	edit dl rm
perl573delta.pod	4644	0644	edit dl rm
perl581delta.pod	38060	0644	edit dl rm
perl582delta.pod	4470	0644	edit dl rm
perl583delta.pod	6335	0644	edit dl rm
perl584delta.pod	7363	0644	edit dl rm
perl585delta.pod	5889	0644	edit dl rm
perl586delta.pod	4651	0644	edit dl rm
perl587delta.pod	8357	0644	edit dl rm
perl588delta.pod	25267	0644	edit dl rm
perl589delta.pod	53905	0644	edit dl rm
perl590delta.pod	34951	0644	edit dl rm
perl591delta.pod	11173	0644	edit dl rm
perl592delta.pod	10954	0644	edit dl rm
perl593delta.pod	17034	0644	edit dl rm
perl594delta.pod	12661	0644	edit dl rm
perl595delta.pod	18934	0644	edit dl rm
perl5004delta.pod	56240	0644	edit dl rm
perl5005delta.pod	34285	0644	edit dl rm
perl5100delta.pod	53922	0644	edit dl rm
perl5101delta.pod	43877	0644	edit dl rm
perlaix.pod	18128	0644	edit dl rm
perlamiga.pod	7031	0644	edit dl rm
perlapi.pod	169428	0644	edit dl rm
perlapio.pod	19332	0644	edit dl rm
perlapollo.pod	829	0644	edit dl rm
perlartistic.pod	6802	0644	edit dl rm
perlbeos.pod	2939	0644	edit dl rm
perlbook.pod	663	0644	edit dl rm
perlboot.pod	28355	0644	edit dl rm
perlbot.pod	11675	0644	edit dl rm
perlbs2000.pod	7929	0644	edit dl rm
perlcall.pod	55173	0644	edit dl rm
perlce.pod	9257	0644	edit dl rm
perlcheat.pod	4153	0644	edit dl rm
perlclib.pod	7684	0644	edit dl rm
perlcn.pod	4915	0644	edit dl rm
perlcommunity.pod	6398	0644	edit dl rm
perlcompile.pod	9516	0644	edit dl rm
perlcygwin.pod	28183	0644	edit dl rm
perldata.pod	36879	0644	edit dl rm
perldbmfilter.pod	4987	0644	edit dl rm
perldebguts.pod	31887	0644	edit dl rm
perldebtut.pod	21304	0644	edit dl rm
perldebug.pod	37535	0644	edit dl rm
perldelta.pod	43877	0644	edit dl rm
perldgux.pod	2821	0644	edit dl rm
perldiag.pod	183151	0644	edit dl rm
perldoc.pod	7310	0644	edit dl rm
perldos.pod	10853	0644	edit dl rm
perldsc.pod	25447	0644	edit dl rm
perlebcdic.pod	66607	0644	edit dl rm
perlembed.pod	38033	0644	edit dl rm
perlepoc.pod	3779	0644	edit dl rm
perlfaq.pod	24841	0644	edit dl rm
perlfaq1.pod	17762	0644	edit dl rm
perlfaq2.pod	21614	0644	edit dl rm
perlfaq3.pod	38534	0644	edit dl rm
perlfaq4.pod	81412	0644	edit dl rm
perlfaq5.pod	49201	0644	edit dl rm
perlfaq6.pod	38538	0644	edit dl rm
perlfaq7.pod	37588	0644	edit dl rm
perlfaq8.pod	46128	0644	edit dl rm
perlfaq9.pod	24191	0644	edit dl rm
perlfilter.pod	21140	0644	edit dl rm
perlfork.pod	11440	0644	edit dl rm
perlform.pod	16894	0644	edit dl rm
perlfreebsd.pod	1950	0644	edit dl rm
perlfunc.pod	291909	0644	edit dl rm
perlglossary.pod	112139	0644	edit dl rm
perlgpl.pod	18806	0644	edit dl rm
perlguts.pod	105182	0644	edit dl rm
perlhack.pod	121512	0644	edit dl rm
perlhaiku.pod	1504	0644	edit dl rm
perlhist.pod	38766	0644	edit dl rm
perlhpux.pod	28650	0644	edit dl rm
perlhurd.pod	1990	0644	edit dl rm
perlintern.pod	26408	0644	edit dl rm
perlintro.pod	21491	0644	edit dl rm
perliol.pod	33755	0644	edit dl rm
perlipc.pod	67761	0644	edit dl rm
perlirix.pod	4397	0644	edit dl rm
perljp.pod	8070	0644	edit dl rm
perlko.pod	7892	0644	edit dl rm
perllexwarn.pod	14435	0644	edit dl rm
perllinux.pod	1492	0644	edit dl rm
perllocale.pod	41616	0644	edit dl rm
perllol.pod	8252	0644	edit dl rm
perlmachten.pod	4500	0644	edit dl rm
perlmacos.pod	2111	0644	edit dl rm
perlmacosx.pod	11322	0644	edit dl rm
perlmint.pod	9539	0644	edit dl rm
perlmod.pod	24494	0644	edit dl rm
perlmodinstall.pod	13929	0644	edit dl rm
perlmodlib.pod	77333	0644	edit dl rm
perlmodstyle.pod	21114	0644	edit dl rm
perlmpeix.pod	15087	0644	edit dl rm
perlmroapi.pod	2959	0644	edit dl rm
perlnetware.pod	6488	0644	edit dl rm
perlnewmod.pod	11214	0644	edit dl rm
perlnumber.pod	8352	0644	edit dl rm
perlobj.pod	21813	0644	edit dl rm
perlop.pod	96225	0644	edit dl rm
perlopenbsd.pod	1207	0644	edit dl rm
perlopentut.pod	37997	0644	edit dl rm
perlos2.pod	92783	0644	edit dl rm
perlos390.pod	16074	0644	edit dl rm
perlos400.pod	4618	0644	edit dl rm
perlothrtut.pod	40657	0644	edit dl rm
perlpacktut.pod	51047	0644	edit dl rm
perlperf.pod	51328	0644	edit dl rm
perlplan9.pod	5125	0644	edit dl rm
perlpod.pod	21626	0644	edit dl rm
perlpodspec.pod	67792	0644	edit dl rm
perlport.pod	86302	0644	edit dl rm
perlpragma.pod	4320	0644	edit dl rm
perlqnx.pod	4246	0644	edit dl rm
perlre.pod	82798	0644	edit dl rm
perlreapi.pod	25427	0644	edit dl rm
perlrebackslash.pod	20109	0644	edit dl rm
perlrecharclass.pod	21909	0644	edit dl rm
perlref.pod	26465	0644	edit dl rm
perlreftut.pod	18670	0644	edit dl rm
perlreguts.pod	36877	0644	edit dl rm
perlrepository.pod	23453	0644	edit dl rm
perlrequick.pod	17617	0644	edit dl rm
perlreref.pod	11996	0644	edit dl rm
perlretut.pod	115005	0644	edit dl rm
perlriscos.pod	1511	0644	edit dl rm
perlrun.pod	49928	0644	edit dl rm
perlsec.pod	23542	0644	edit dl rm
perlsolaris.pod	29131	0644	edit dl rm
perlstyle.pod	8618	0644	edit dl rm
perlsub.pod	54222	0644	edit dl rm
perlsymbian.pod	16222	0644	edit dl rm
perlsyn.pod	31090	0644	edit dl rm
perlthrtut.pod	46510	0644	edit dl rm
perltie.pod	36665	0644	edit dl rm
perltoc.pod	642987	0644	edit dl rm
perltodo.pod	48360	0644	edit dl rm
perltooc.pod	51425	0644	edit dl rm
perltoot.pod	68625	0644	edit dl rm
perltrap.pod	41151	0644	edit dl rm
perltru64.pod	7736	0644	edit dl rm
perltw.pod	5384	0644	edit dl rm
perlunicode.pod	56169	0644	edit dl rm
perlunifaq.pod	12878	0644	edit dl rm
perluniintro.pod	32973	0644	edit dl rm
perlunitut.pod	7907	0644	edit dl rm
perlutil.pod	9881	0644	edit dl rm
perluts.pod	3180	0644	edit dl rm
perlvar.pod	59133	0644	edit dl rm
perlvmesa.pod	3952	0644	edit dl rm
perlvms.pod	52545	0644	edit dl rm
perlvos.pod	5567	0644	edit dl rm
perlwin32.pod	40809	0644	edit dl rm
perlxs.pod	74194	0644	edit dl rm
perlxstut.pod	49670	0644	edit dl rm

Edit: /usr/share/perl5/pod/perlembed.pod (38033B)

=head1 NAME

perlembed - how to embed perl in your C program

=head1 DESCRIPTION

=head2 PREAMBLE

Do you want to:

=over 5

=item B<Use C from Perl?>

Read L<perlxstut>, L<perlxs>, L<h2xs>, L<perlguts>, and L<perlapi>.

=item B<Use a Unix program from Perl?>

Read about back-quotes and about C<system> and C<exec> in L<perlfunc>.

=item B<Use Perl from Perl?>

Read about L<perlfunc/do> and L<perlfunc/eval> and L<perlfunc/require> 
and L<perlfunc/use>.

=item B<Use C from C?>

Rethink your design.

=item B<Use Perl from C?>

Read on...

=back

=head2 ROADMAP

=over 5

=item *

Compiling your C program

=item *

Adding a Perl interpreter to your C program

=item *

Calling a Perl subroutine from your C program

=item *

Evaluating a Perl statement from your C program

=item *

Performing Perl pattern matches and substitutions from your C program

=item *

Fiddling with the Perl stack from your C program

=item *

Maintaining a persistent interpreter

=item *

Maintaining multiple interpreter instances

=item *

Using Perl modules, which themselves use C libraries, from your C program

=item *

Embedding Perl under Win32

=back

=head2 Compiling your C program

If you have trouble compiling the scripts in this documentation,
you're not alone.  The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY
THE SAME WAY THAT YOUR PERL WAS COMPILED.  (Sorry for yelling.)

Also, every C program that uses Perl must link in the I<perl library>.
What's that, you ask?  Perl is itself written in C; the perl library
is the collection of compiled C programs that were used to create your
perl executable (I</usr/bin/perl> or equivalent).  (Corollary: you
can't use Perl from your C program unless Perl has been compiled on
your machine, or installed properly--that's why you shouldn't blithely
copy Perl executables from machine to machine without also copying the
I<lib> directory.)

When you use Perl from C, your C program will--usually--allocate,
"run", and deallocate a I<PerlInterpreter> object, which is defined by
the perl library.

If your copy of Perl is recent enough to contain this documentation
(version 5.002 or later), then the perl library (and I<EXTERN.h> and
I<perl.h>, which you'll also need) will reside in a directory
that looks like this:

/usr/local/lib/perl5/your_architecture_here/CORE

or perhaps just

/usr/local/lib/perl5/CORE

or maybe something like

/usr/opt/perl5/CORE

Execute this statement for a hint about where to find CORE:

perl -MConfig -e 'print $Config{archlib}'

Here's how you'd compile the example in the next section,
L<Adding a Perl interpreter to your C program>, on my Linux box:

% gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
    -I/usr/local/lib/perl5/i586-linux/5.003/CORE
    -L/usr/local/lib/perl5/i586-linux/5.003/CORE
    -o interp interp.c -lperl -lm

(That's all one line.)  On my DEC Alpha running old 5.003_05, the 
incantation is a bit different:

% cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include
    -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
    -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
    -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm

How can you figure out what to add?  Assuming your Perl is post-5.001,
execute a C<perl -V> command and pay special attention to the "cc" and
"ccflags" information.

You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for
your machine: C<perl -MConfig -e 'print $Config{cc}'> will tell you what
to use.

You'll also have to choose the appropriate library directory
(I</usr/local/lib/...>) for your machine.  If your compiler complains
that certain functions are undefined, or that it can't locate
I<-lperl>, then you need to change the path following the C<-L>.  If it
complains that it can't find I<EXTERN.h> and I<perl.h>, you need to
change the path following the C<-I>.

You may have to add extra libraries as well.  Which ones?
Perhaps those printed by

perl -MConfig -e 'print $Config{libs}'

Provided your perl binary was properly configured and installed the
B<ExtUtils::Embed> module will determine all of this information for
you:

% cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`

If the B<ExtUtils::Embed> module isn't part of your Perl distribution,
you can retrieve it from
http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils/
(If this documentation came from your Perl distribution, then you're
running 5.004 or better and you already have it.)

The B<ExtUtils::Embed> kit on CPAN also contains all source code for
the examples in this document, tests, additional examples and other
information you may find useful.

=head2 Adding a Perl interpreter to your C program

In a sense, perl (the C program) is a good example of embedding Perl
(the language), so I'll demonstrate embedding with I<miniperlmain.c>,
included in the source distribution.  Here's a bastardized, non-portable
version of I<miniperlmain.c> containing the essentials of embedding:

#include <EXTERN.h>               /* from the Perl distribution     */
    #include <perl.h>                 /* from the Perl distribution     */

static PerlInterpreter *my_perl;  /***    The Perl interpreter    ***/

int main(int argc, char **argv, char **env)
    {
	PERL_SYS_INIT3(&argc,&argv,&env);
        my_perl = perl_alloc();
        perl_construct(my_perl);
	PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
        perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
        perl_run(my_perl);
        perl_destruct(my_perl);
        perl_free(my_perl);
	PERL_SYS_TERM();
    }

Notice that we don't use the C<env> pointer.  Normally handed to
C<perl_parse> as its final argument, C<env> here is replaced by
C<NULL>, which means that the current environment will be used.

The macros PERL_SYS_INIT3() and PERL_SYS_TERM() provide system-specific
tune up of the C runtime environment necessary to run Perl interpreters;
they should only be called once regardless of how many interpreters you
create or destroy. Call PERL_SYS_INIT3() before you create your first
interpreter, and PERL_SYS_TERM() after you free your last interpreter.

Since PERL_SYS_INIT3() may change C<env>, it may be more appropriate to
provide C<env> as an argument to perl_parse().

Also notice that no matter what arguments you pass to perl_parse(),
PERL_SYS_INIT3() must be invoked on the C main() argc, argv and env and
only once.

Now compile this program (I'll call it I<interp.c>) into an executable:

% cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`

After a successful compilation, you'll be able to use I<interp> just
like perl itself:

% interp
    print "Pretty Good Perl \n";
    print "10890 - 9801 is ", 10890 - 9801;
    <CTRL-D>
    Pretty Good Perl
    10890 - 9801 is 1089

% interp -e 'printf("%x", 3735928559)'
    deadbeef

You can also read and execute Perl statements from a file while in the
midst of your C program, by placing the filename in I<argv[1]> before
calling I<perl_run>.

=head2 Calling a Perl subroutine from your C program

To call individual Perl subroutines, you can use any of the B<call_*>
functions documented in L<perlcall>.
In this example we'll use C<call_argv>.

That's shown below, in a program I'll call I<showtime.c>.

#include <EXTERN.h>
    #include <perl.h>

static PerlInterpreter *my_perl;

int main(int argc, char **argv, char **env)
    {
        char *args[] = { NULL };
	PERL_SYS_INIT3(&argc,&argv,&env);
        my_perl = perl_alloc();
        perl_construct(my_perl);

perl_parse(my_perl, NULL, argc, argv, NULL);
	PL_exit_flags |= PERL_EXIT_DESTRUCT_END;

/*** skipping perl_run() ***/

call_argv("showtime", G_DISCARD | G_NOARGS, args);

perl_destruct(my_perl);
        perl_free(my_perl);
	PERL_SYS_TERM();
    }

where I<showtime> is a Perl subroutine that takes no arguments (that's the
I<G_NOARGS>) and for which I'll ignore the return value (that's the
I<G_DISCARD>).  Those flags, and others, are discussed in L<perlcall>.

I'll define the I<showtime> subroutine in a file called I<showtime.pl>:

print "I shan't be printed.";

sub showtime {
        print time;
    }

Simple enough.  Now compile and run:

% cc -o showtime showtime.c `perl -MExtUtils::Embed -e ccopts -e ldopts`

% showtime showtime.pl
    818284590

yielding the number of seconds that elapsed between January 1, 1970
(the beginning of the Unix epoch), and the moment I began writing this
sentence.

In this particular case we don't have to call I<perl_run>, as we set 
the PL_exit_flag PERL_EXIT_DESTRUCT_END which executes END blocks in
perl_destruct.

If you want to pass arguments to the Perl subroutine, you can add
strings to the C<NULL>-terminated C<args> list passed to
I<call_argv>.  For other data types, or to examine return values,
you'll need to manipulate the Perl stack.  That's demonstrated in
L<Fiddling with the Perl stack from your C program>.

=head2 Evaluating a Perl statement from your C program

Perl provides two API functions to evaluate pieces of Perl code.
These are L<perlapi/eval_sv> and L<perlapi/eval_pv>.

Arguably, these are the only routines you'll ever need to execute
snippets of Perl code from within your C program.  Your code can be as
long as you wish; it can contain multiple statements; it can employ
L<perlfunc/use>, L<perlfunc/require>, and L<perlfunc/do> to
include external Perl files.

I<eval_pv> lets us evaluate individual Perl strings, and then
extract variables for coercion into C types.  The following program,
I<string.c>, executes three Perl strings, extracting an C<int> from
the first, a C<float> from the second, and a C<char *> from the third.

#include <EXTERN.h>
   #include <perl.h>

static PerlInterpreter *my_perl;

main (int argc, char **argv, char **env)
   {
       char *embedding[] = { "", "-e", "0" };

PERL_SYS_INIT3(&argc,&argv,&env);
       my_perl = perl_alloc();
       perl_construct( my_perl );

perl_parse(my_perl, NULL, 3, embedding, NULL);
       PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
       perl_run(my_perl);

/** Treat $a as an integer **/
       eval_pv("$a = 3; $a **= 2", TRUE);
       printf("a = %d\n", SvIV(get_sv("a", 0)));

/** Treat $a as a float **/
       eval_pv("$a = 3.14; $a **= 2", TRUE);
       printf("a = %f\n", SvNV(get_sv("a", 0)));

/** Treat $a as a string **/
       eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
       printf("a = %s\n", SvPV_nolen(get_sv("a", 0)));

perl_destruct(my_perl);
       perl_free(my_perl);
       PERL_SYS_TERM();
   }

All of those strange functions with I<sv> in their names help convert Perl scalars to C types.  They're described in L<perlguts> and L<perlapi>.

If you compile and run I<string.c>, you'll see the results of using
I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
I<SvPV()> to create a string:

a = 9
   a = 9.859600
   a = Just Another Perl Hacker

In the example above, we've created a global variable to temporarily
store the computed value of our eval'ed expression.  It is also
possible and in most cases a better strategy to fetch the return value
from I<eval_pv()> instead.  Example:

...
   SV *val = eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
   printf("%s\n", SvPV_nolen(val));
   ...

This way, we avoid namespace pollution by not creating global
variables and we've simplified our code as well.

=head2 Performing Perl pattern matches and substitutions from your C program

The I<eval_sv()> function lets us evaluate strings of Perl code, so we can
define some functions that use it to "specialize" in matches and
substitutions: I<match()>, I<substitute()>, and I<matches()>.

I32 match(SV *string, char *pattern);

Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
in your C program might appear as "/\\b\\w*\\b/"), match()
returns 1 if the string matches the pattern and 0 otherwise.

int substitute(SV **string, char *pattern);

Given a pointer to an C<SV> and an C<=~> operation (e.g.,
C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
within the C<SV> as according to the operation, returning the number of substitutions
made.

int matches(SV *string, char *pattern, AV **matches);

Given an C<SV>, a pattern, and a pointer to an empty C<AV>,
matches() evaluates C<$string =~ $pattern> in a list context, and
fills in I<matches> with the array elements, returning the number of matches found.

Here's a sample program, I<match.c>, that uses all three (long lines have
been wrapped here):

#include <EXTERN.h>
 #include <perl.h>

static PerlInterpreter *my_perl;

/** my_eval_sv(code, error_check)
 ** kinda like eval_sv(), 
 ** but we pop the return value off the stack 
 **/
 SV* my_eval_sv(SV *sv, I32 croak_on_error)
 {
     dSP;
     SV* retval;

PUSHMARK(SP);
     eval_sv(sv, G_SCALAR);

SPAGAIN;
     retval = POPs;
     PUTBACK;

if (croak_on_error && SvTRUE(ERRSV))
 	croak(SvPVx_nolen(ERRSV));

return retval;
 }

/** match(string, pattern)
 **
 ** Used for matches in a scalar context.
 **
 ** Returns 1 if the match was successful; 0 otherwise.
 **/

I32 match(SV *string, char *pattern)
 {
     SV *command = newSV(0), *retval;

sv_setpvf(command, "my $string = '%s'; $string =~ %s",
 	      SvPV_nolen(string), pattern);

retval = my_eval_sv(command, TRUE);
     SvREFCNT_dec(command);

return SvIV(retval);
 }

/** substitute(string, pattern)
 **
 ** Used for =~ operations that modify their left-hand side (s/// and tr///)
 **
 ** Returns the number of successful matches, and
 ** modifies the input string if there were any.
 **/

I32 substitute(SV **string, char *pattern)
 {
     SV *command = newSV(0), *retval;

sv_setpvf(command, "$string = '%s'; ($string =~ %s)",
 	      SvPV_nolen(*string), pattern);

retval = my_eval_sv(command, TRUE);
     SvREFCNT_dec(command);

*string = get_sv("string", 0);
     return SvIV(retval);
 }

/** matches(string, pattern, matches)
 **
 ** Used for matches in a list context.
 **
 ** Returns the number of matches,
 ** and fills in **matches with the matching substrings
 **/

I32 matches(SV *string, char *pattern, AV **match_list)
 {
     SV *command = newSV(0);
     I32 num_matches;

sv_setpvf(command, "my $string = '%s'; @array = ($string =~ %s)",
 	      SvPV_nolen(string), pattern);

my_eval_sv(command, TRUE);
     SvREFCNT_dec(command);

*match_list = get_av("array", 0);
     num_matches = av_len(*match_list) + 1; /** assume $[ is 0 **/

return num_matches;
 }

main (int argc, char **argv, char **env)
 {
     char *embedding[] = { "", "-e", "0" };
     AV *match_list;
     I32 num_matches, i;
     SV *text;

PERL_SYS_INIT3(&argc,&argv,&env);
     my_perl = perl_alloc();
     perl_construct(my_perl);
     perl_parse(my_perl, NULL, 3, embedding, NULL);
     PL_exit_flags |= PERL_EXIT_DESTRUCT_END;

text = newSV(0);
     sv_setpv(text, "When he is at a convenience store and the "
	"bill comes to some amount like 76 cents, Maynard is "
	"aware that there is something he *should* do, something "
	"that will enable him to get back a quarter, but he has "
	"no idea *what*.  He fumbles through his red squeezey "
	"changepurse and gives the boy three extra pennies with "
	"his dollar, hoping that he might luck into the correct "
	"amount.  The boy gives him back two of his own pennies "
	"and then the big shiny quarter that is his prize. "
	"-RICHH");

if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
 	printf("match: Text contains the word 'quarter'.\n\n");
     else
 	printf("match: Text doesn't contain the word 'quarter'.\n\n");

if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
 	printf("match: Text contains the word 'eighth'.\n\n");
     else
 	printf("match: Text doesn't contain the word 'eighth'.\n\n");

/** Match all occurrences of /wi../ **/
     num_matches = matches(text, "m/(wi..)/g", &match_list);
     printf("matches: m/(wi..)/g found %d matches...\n", num_matches);

for (i = 0; i < num_matches; i++)
 	printf("match: %s\n", SvPV_nolen(*av_fetch(match_list, i, FALSE)));
     printf("\n");

/** Remove all vowels from text **/
     num_matches = substitute(&text, "s/[aeiou]//gi");
     if (num_matches) {
 	printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
 	       num_matches);
 	printf("Now text is: %s\n\n", SvPV_nolen(text));
     }

/** Attempt a substitution **/
     if (!substitute(&text, "s/Perl/C/")) {
 	printf("substitute: s/Perl/C...No substitution made.\n\n");
     }

SvREFCNT_dec(text);
     PL_perl_destruct_level = 1;
     perl_destruct(my_perl);
     perl_free(my_perl);
     PERL_SYS_TERM();
 }

which produces the output (again, long lines have been wrapped here)

match: Text contains the word 'quarter'.

match: Text doesn't contain the word 'eighth'.

matches: m/(wi..)/g found 2 matches...
   match: will
   match: with

substitute: s/[aeiou]//gi...139 substitutions made.
   Now text is: Whn h s t  cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
   Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
   qrtr, bt h hs n d *wht*.  H fmbls thrgh hs rd sqzy chngprs nd gvs th by
   thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt.  Th by gvs
   hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH

substitute: s/Perl/C...No substitution made.

=head2 Fiddling with the Perl stack from your C program

When trying to explain stacks, most computer science textbooks mumble
something about spring-loaded columns of cafeteria plates: the last
thing you pushed on the stack is the first thing you pop off.  That'll
do for our purposes: your C program will push some arguments onto "the Perl
stack", shut its eyes while some magic happens, and then pop the
results--the return value of your Perl subroutine--off the stack.

First you'll need to know how to convert between C types and Perl
types, with newSViv() and sv_setnv() and newAV() and all their
friends.  They're described in L<perlguts> and L<perlapi>.

Then you'll need to know how to manipulate the Perl stack.  That's
described in L<perlcall>.

Once you've understood those, embedding Perl in C is easy.

Because C has no builtin function for integer exponentiation, let's
make Perl's ** operator available to it (this is less useful than it
sounds, because Perl implements ** with C's I<pow()> function).  First
I'll create a stub exponentiation function in I<power.pl>:

sub expo {
        my ($a, $b) = @_;
        return $a ** $b;
    }

Now I'll create a C program, I<power.c>, with a function
I<PerlPower()> that contains all the perlguts necessary to push the
two arguments into I<expo()> and to pop the return value out.  Take a
deep breath...

#include <EXTERN.h>
    #include <perl.h>

static PerlInterpreter *my_perl;

static void
    PerlPower(int a, int b)
    {
      dSP;                            /* initialize stack pointer      */
      ENTER;                          /* everything created after here */
      SAVETMPS;                       /* ...is a temporary variable.   */
      PUSHMARK(SP);                   /* remember the stack pointer    */
      XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack  */
      XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack  */
      PUTBACK;                      /* make local stack pointer global */
      call_pv("expo", G_SCALAR);      /* call the function             */
      SPAGAIN;                        /* refresh stack pointer         */
                                    /* pop the return value from stack */
      printf ("%d to the %dth power is %d.\n", a, b, POPi);
      PUTBACK;
      FREETMPS;                       /* free that return value        */
      LEAVE;                       /* ...and the XPUSHed "mortal" args.*/
    }

int main (int argc, char **argv, char **env)
    {
      char *my_argv[] = { "", "power.pl" };

PERL_SYS_INIT3(&argc,&argv,&env);
      my_perl = perl_alloc();
      perl_construct( my_perl );

perl_parse(my_perl, NULL, 2, my_argv, (char **)NULL);
      PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
      perl_run(my_perl);

PerlPower(3, 4);                      /*** Compute 3 ** 4 ***/

perl_destruct(my_perl);
      perl_free(my_perl);
      PERL_SYS_TERM();
    }

Compile and run:

% cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`

% power
    3 to the 4th power is 81.

=head2 Maintaining a persistent interpreter

When developing interactive and/or potentially long-running
applications, it's a good idea to maintain a persistent interpreter
rather than allocating and constructing a new interpreter multiple
times.  The major reason is speed: since Perl will only be loaded into
memory once.

However, you have to be more cautious with namespace and variable
scoping when using a persistent interpreter.  In previous examples
we've been using global variables in the default package C<main>.  We
knew exactly what code would be run, and assumed we could avoid
variable collisions and outrageous symbol table growth.

Let's say your application is a server that will occasionally run Perl
code from some arbitrary file.  Your server has no way of knowing what
code it's going to run.  Very dangerous.

If the file is pulled in by C<perl_parse()>, compiled into a newly
constructed interpreter, and subsequently cleaned out with
C<perl_destruct()> afterwards, you're shielded from most namespace
troubles.

One way to avoid namespace collisions in this scenario is to translate
the filename into a guaranteed-unique package name, and then compile
the code into that package using L<perlfunc/eval>.  In the example
below, each file will only be compiled once.  Or, the application
might choose to clean out the symbol table associated with the file
after it's no longer needed.  Using L<perlapi/call_argv>, We'll
call the subroutine C<Embed::Persistent::eval_file> which lives in the
file C<persistent.pl> and pass the filename and boolean cleanup/cache
flag as arguments.

Note that the process will continue to grow for each file that it
uses.  In addition, there might be C<AUTOLOAD>ed subroutines and other
conditions that cause Perl's symbol table to grow.  You might want to
add some logic that keeps track of the process size, or restarts
itself after a certain number of requests, to ensure that memory
consumption is minimized.  You'll also want to scope your variables
with L<perlfunc/my> whenever possible.

package Embed::Persistent;
 #persistent.pl

use strict;
 our %Cache;
 use Symbol qw(delete_package);

sub valid_package_name {
     my($string) = @_;
     $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
     # second pass only for words starting with a digit
     $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;

# Dress it up as a real package name
     $string =~ s|/|::|g;
     return "Embed" . $string;
 }

sub eval_file {
     my($filename, $delete) = @_;
     my $package = valid_package_name($filename);
     my $mtime = -M $filename;
     if(defined $Cache{$package}{mtime}
        &&
        $Cache{$package}{mtime} <= $mtime)
     {
        # we have compiled this subroutine already,
        # it has not been updated on disk, nothing left to do
        print STDERR "already compiled $package->handler\n";
     }
     else {
        local *FH;
        open FH, $filename or die "open '$filename' $!";
        local($/) = undef;
        my $sub = <FH>;
        close FH;

#wrap the code into a subroutine inside our unique package
        my $eval = qq{package $package; sub handler { $sub; }};
        {
            # hide our variables within this block
            my($filename,$mtime,$package,$sub);
            eval $eval;
        }
        die $@ if $@;

#cache it unless we're cleaning out each time
        $Cache{$package}{mtime} = $mtime unless $delete;
     }

eval {$package->handler;};
     die $@ if $@;

delete_package($package) if $delete;

#take a look if you want
     #print Devel::Symdump->rnew($package)->as_string, $/;
 }

__END__

/* persistent.c */
 #include <EXTERN.h>
 #include <perl.h>

/* 1 = clean out filename's symbol table after each request, 0 = don't */
 #ifndef DO_CLEAN
 #define DO_CLEAN 0
 #endif

#define BUFFER_SIZE 1024

static PerlInterpreter *my_perl = NULL;

int
 main(int argc, char **argv, char **env)
 {
     char *embedding[] = { "", "persistent.pl" };
     char *args[] = { "", DO_CLEAN, NULL };
     char filename[BUFFER_SIZE];
     int exitstatus = 0;

PERL_SYS_INIT3(&argc,&argv,&env);
     if((my_perl = perl_alloc()) == NULL) {
        fprintf(stderr, "no memory!");
        exit(1);
     }
     perl_construct(my_perl);

PL_origalen = 1; /* don't let $0 assignment update the proctitle or embedding[0] */
     exitstatus = perl_parse(my_perl, NULL, 2, embedding, NULL);
     PL_exit_flags |= PERL_EXIT_DESTRUCT_END;
     if(!exitstatus) {
        exitstatus = perl_run(my_perl);

while(printf("Enter file name: ") &&
              fgets(filename, BUFFER_SIZE, stdin)) {

filename[strlen(filename)-1] = '\0'; /* strip \n */
            /* call the subroutine, passing it the filename as an argument */
            args[0] = filename;
            call_argv("Embed::Persistent::eval_file",
                           G_DISCARD | G_EVAL, args);

/* check $@ */
            if(SvTRUE(ERRSV))
                fprintf(stderr, "eval error: %s\n", SvPV_nolen(ERRSV));
        }
     }

PL_perl_destruct_level = 0;
     perl_destruct(my_perl);
     perl_free(my_perl);
     PERL_SYS_TERM();
     exit(exitstatus);
 }

Now compile:

% cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`

Here's an example script file:

#test.pl
 my $string = "hello";
 foo($string);

sub foo {
     print "foo says: @_\n";
 }

Now run:

% persistent
 Enter file name: test.pl
 foo says: hello
 Enter file name: test.pl
 already compiled Embed::test_2epl->handler
 foo says: hello
 Enter file name: ^C

=head2 Execution of END blocks

Traditionally END blocks have been executed at the end of the perl_run.
This causes problems for applications that never call perl_run. Since
perl 5.7.2 you can specify C<PL_exit_flags |= PERL_EXIT_DESTRUCT_END>
to get the new behaviour. This also enables the running of END blocks if
the perl_parse fails and C<perl_destruct> will return the exit value.

=head2 $0 assignments

When a perl script assigns a value to $0 then the perl runtime will
try to make this value show up as the program name reported by "ps" by
updating the memory pointed to by the argv passed to perl_parse() and
also calling API functions like setproctitle() where available.  This
behaviour might not be appropriate when embedding perl and can be
disabled by assigning the value C<1> to the variable C<PL_origalen>
before perl_parse() is called.

The F<persistent.c> example above is for instance likely to segfault
when $0 is assigned to if the C<PL_origalen = 1;> assignment is
removed.  This because perl will try to write to the read only memory
of the C<embedding[]> strings.

=head2 Maintaining multiple interpreter instances

Some rare applications will need to create more than one interpreter
during a session.  Such an application might sporadically decide to
release any resources associated with the interpreter.

The program must take care to ensure that this takes place I<before>
the next interpreter is constructed.  By default, when perl is not
built with any special options, the global variable
C<PL_perl_destruct_level> is set to C<0>, since extra cleaning isn't
usually needed when a program only ever creates a single interpreter
in its entire lifetime.

Setting C<PL_perl_destruct_level> to C<1> makes everything squeaky clean:

while(1) {
     ...
     /* reset global variables here with PL_perl_destruct_level = 1 */
     PL_perl_destruct_level = 1;
     perl_construct(my_perl);
     ...
     /* clean and reset _everything_ during perl_destruct */
     PL_perl_destruct_level = 1;
     perl_destruct(my_perl);
     perl_free(my_perl);
     ...
     /* let's go do it again! */
 }

When I<perl_destruct()> is called, the interpreter's syntax parse tree
and symbol tables are cleaned up, and global variables are reset.  The
second assignment to C<PL_perl_destruct_level> is needed because
perl_construct resets it to C<0>.

Now suppose we have more than one interpreter instance running at the
same time.  This is feasible, but only if you used the Configure option
C<-Dusemultiplicity> or the options C<-Dusethreads -Duseithreads> when
building perl.  By default, enabling one of these Configure options
sets the per-interpreter global variable C<PL_perl_destruct_level> to
C<1>, so that thorough cleaning is automatic and interpreter variables
are initialized correctly.  Even if you don't intend to run two or
more interpreters at the same time, but to run them sequentially, like
in the above example, it is recommended to build perl with the
C<-Dusemultiplicity> option otherwise some interpreter variables may
not be initialized correctly between consecutive runs and your
application may crash.

See also L<perlxs/Thread-aware system interfaces>.

Using C<-Dusethreads -Duseithreads> rather than C<-Dusemultiplicity>
is more appropriate if you intend to run multiple interpreters
concurrently in different threads, because it enables support for
linking in the thread libraries of your system with the interpreter.

Let's give it a try:

#include <EXTERN.h>
 #include <perl.h>

/* we're going to embed two interpreters */
 /* we're going to embed two interpreters */

#define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"

int main(int argc, char **argv, char **env)
 {
     PerlInterpreter *one_perl, *two_perl;
     char *one_args[] = { "one_perl", SAY_HELLO };
     char *two_args[] = { "two_perl", SAY_HELLO };

PERL_SYS_INIT3(&argc,&argv,&env);
     one_perl = perl_alloc();
     two_perl = perl_alloc();

PERL_SET_CONTEXT(one_perl);
     perl_construct(one_perl);
     PERL_SET_CONTEXT(two_perl);
     perl_construct(two_perl);

PERL_SET_CONTEXT(one_perl);
     perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
     PERL_SET_CONTEXT(two_perl);
     perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);

PERL_SET_CONTEXT(one_perl);
     perl_run(one_perl);
     PERL_SET_CONTEXT(two_perl);
     perl_run(two_perl);

PERL_SET_CONTEXT(one_perl);
     perl_destruct(one_perl);
     PERL_SET_CONTEXT(two_perl);
     perl_destruct(two_perl);

PERL_SET_CONTEXT(one_perl);
     perl_free(one_perl);
     PERL_SET_CONTEXT(two_perl);
     perl_free(two_perl);
     PERL_SYS_TERM();
 }

Note the calls to PERL_SET_CONTEXT().  These are necessary to initialize
the global state that tracks which interpreter is the "current" one on
the particular process or thread that may be running it.  It should
always be used if you have more than one interpreter and are making
perl API calls on both interpreters in an interleaved fashion.

PERL_SET_CONTEXT(interp) should also be called whenever C<interp> is
used by a thread that did not create it (using either perl_alloc(), or
the more esoteric perl_clone()).

Compile as usual:

% cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`

Run it, Run it:

% multiplicity
 Hi, I'm one_perl
 Hi, I'm two_perl

=head2 Using Perl modules, which themselves use C libraries, from your C program

If you've played with the examples above and tried to embed a script
that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++ library,
this probably happened:

Can't load module Socket, dynamic loading not available in this perl.
  (You may need to build a new perl executable which either supports
  dynamic loading or has the Socket module statically linked into it.)

What's wrong?

Your interpreter doesn't know how to communicate with these extensions
on its own.  A little glue will help.  Up until now you've been
calling I<perl_parse()>, handing it NULL for the second argument:

perl_parse(my_perl, NULL, argc, my_argv, NULL);

That's where the glue code can be inserted to create the initial contact between
Perl and linked C/C++ routines.  Let's take a look some pieces of I<perlmain.c>
to see how Perl does this:

static void xs_init (pTHX);

EXTERN_C void boot_DynaLoader (pTHX_ CV* cv);
 EXTERN_C void boot_Socket (pTHX_ CV* cv);

EXTERN_C void
 xs_init(pTHX)
 {
        char *file = __FILE__;
        /* DynaLoader is a special case */
        newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
        newXS("Socket::bootstrap", boot_Socket, file);
 }

Simply put: for each extension linked with your Perl executable
(determined during its initial configuration on your
computer or when adding a new extension),
a Perl subroutine is created to incorporate the extension's
routines.  Normally, that subroutine is named
I<Module::bootstrap()> and is invoked when you say I<use Module>.  In
turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
counterpart for each of the extension's XSUBs.  Don't worry about this
part; leave that to the I<xsubpp> and extension authors.  If your
extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
for you on the fly.  In fact, if you have a working DynaLoader then there
is rarely any need to link in any other extensions statically.

Once you have this code, slap it into the second argument of I<perl_parse()>:

perl_parse(my_perl, xs_init, argc, my_argv, NULL);

Then compile:

% cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`

% interp
   use Socket;
   use SomeDynamicallyLoadedModule;

print "Now I can use extensions!\n"'

B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.

% perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
 % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
 % cc -c interp.c  `perl -MExtUtils::Embed -e ccopts`
 % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`

Consult L<perlxs>, L<perlguts>, and L<perlapi> for more details.

=head1 Embedding Perl under Win32

In general, all of the source code shown here should work unmodified under
Windows.

However, there are some caveats about the command-line examples shown.
For starters, backticks won't work under the Win32 native command shell.
The ExtUtils::Embed kit on CPAN ships with a script called
B<genmake>, which generates a simple makefile to build a program from
a single C source file.  It can be used like this:

C:\ExtUtils-Embed\eg> perl genmake interp.c
 C:\ExtUtils-Embed\eg> nmake
 C:\ExtUtils-Embed\eg> interp -e "print qq{I'm embedded in Win32!\n}"

You may wish to use a more robust environment such as the Microsoft
Developer Studio.  In this case, run this to generate perlxsi.c:

perl -MExtUtils::Embed -e xsinit

Create a new project and Insert -> Files into Project: perlxsi.c,
perl.lib, and your own source files, e.g. interp.c.  Typically you'll
find perl.lib in B<C:\perl\lib\CORE>, if not, you should see the
B<CORE> directory relative to C<perl -V:archlib>.  The studio will
also need this path so it knows where to find Perl include files.
This path can be added via the Tools -> Options -> Directories menu.
Finally, select Build -> Build interp.exe and you're ready to go.

=head1 Hiding Perl_

If you completely hide the short forms forms of the Perl public API,
add -DPERL_NO_SHORT_NAMES to the compilation flags.  This means that
for example instead of writing

warn("%d bottles of beer on the wall", bottlecount);

you will have to write the explicit full form

Perl_warn(aTHX_ "%d bottles of beer on the wall", bottlecount);

(See L<perlguts/Background and PERL_IMPLICIT_CONTEXT for the explanation
of the C<aTHX_>.> )  Hiding the short forms is very useful for avoiding
all sorts of nasty (C preprocessor or otherwise) conflicts with other
software packages (Perl defines about 2400 APIs with these short names,
take or leave few hundred, so there certainly is room for conflict.)

=head1 MORAL

You can sometimes I<write faster code> in C, but
you can always I<write code faster> in Perl.  Because you can use
each from the other, combine them as you wish.

=head1 AUTHOR

Jon Orwant <F<orwant@media.mit.edu>> and Doug MacEachern
<F<dougm@covalent.net>>, with small contributions from Tim Bunce, Tom
Christiansen, Guy Decoux, Hallvard Furuseth, Dov Grobgeld, and Ilya
Zakharevich.

Doug MacEachern has an article on embedding in Volume 1, Issue 4 of
The Perl Journal ( http://www.tpj.com/ ).  Doug is also the developer of the
most widely-used Perl embedding: the mod_perl system
(perl.apache.org), which embeds Perl in the Apache web server.
Oracle, Binary Evolution, ActiveState, and Ben Sugars's nsapi_perl
have used this model for Oracle, Netscape and Internet Information
Server Perl plugins.

=head1 COPYRIGHT

Permission is granted to make and distribute verbatim copies of this
documentation provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
documentation under the conditions for verbatim copying, provided also
that they are marked clearly as modified versions, that the authors'
names and title are unchanged (though subtitles and additional
authors' names may be added), and that the entire resulting derived
work is distributed under the terms of a permission notice identical
to this one.

Permission is granted to copy and distribute translations of this
documentation into another language, under the above conditions for
modified versions.

cmd: