FM / pod

/usr/share/perl5/pod

Name	Size	Mode	Actions
perl.pod	16270	0644	edit dl rm
perl56delta.pod	107201	0644	edit dl rm
perl58delta.pod	115165	0644	edit dl rm
perl561delta.pod	124713	0644	edit dl rm
perl581delta.pod	38061	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	25272	0644	edit dl rm
perl589delta.pod	53900	0644	edit dl rm
perl5004delta.pod	56240	0644	edit dl rm
perl5005delta.pod	34283	0644	edit dl rm
perl5100delta.pod	55535	0644	edit dl rm
perl5101delta.pod	43888	0644	edit dl rm
perl5120delta.pod	89272	0644	edit dl rm
perl5121delta.pod	10141	0644	edit dl rm
perl5122delta.pod	9603	0644	edit dl rm
perl5123delta.pod	4100	0644	edit dl rm
perl5124delta.pod	3672	0644	edit dl rm
perl5125delta.pod	7683	0644	edit dl rm
perl5140delta.pod	144324	0644	edit dl rm
perl5141delta.pod	7966	0644	edit dl rm
perl5142delta.pod	6892	0644	edit dl rm
perl5143delta.pod	7760	0644	edit dl rm
perl5144delta.pod	6327	0644	edit dl rm
perl5160delta.pod	133651	0644	edit dl rm
perl5161delta.pod	6142	0644	edit dl rm
perl5162delta.pod	3594	0644	edit dl rm
perl5163delta.pod	4085	0644	edit dl rm
perl5180delta.pod	119431	0644	edit dl rm
perl5181delta.pod	6595	0644	edit dl rm
perl5182delta.pod	5335	0644	edit dl rm
perl5184delta.pod	4642	0644	edit dl rm
perl5200delta.pod	115699	0644	edit dl rm
perl5201delta.pod	10899	0644	edit dl rm
perl5202delta.pod	12509	0644	edit dl rm
perl5203delta.pod	9392	0644	edit dl rm
perl5220delta.pod	130963	0644	edit dl rm
perl5221delta.pod	10767	0644	edit dl rm
perl5222delta.pod	12629	0644	edit dl rm
perl5223delta.pod	8456	0644	edit dl rm
perl5224delta.pod	4460	0644	edit dl rm
perl5240delta.pod	64927	0644	edit dl rm
perl5241delta.pod	8215	0644	edit dl rm
perl5242delta.pod	4113	0644	edit dl rm
perl5243delta.pod	11428	0644	edit dl rm
perl5244delta.pod	4510	0644	edit dl rm
perl5260delta.pod	101836	0644	edit dl rm
perl5261delta.pod	7927	0644	edit dl rm
perl5262delta.pod	7880	0644	edit dl rm
perl5263delta.pod	7063	0644	edit dl rm
perl5280delta.pod	72113	0644	edit dl rm
perlaix.pod	20437	0644	edit dl rm
perlamiga.pod	5749	0644	edit dl rm
perlandroid.pod	7871	0644	edit dl rm
perlapi.pod	443535	0644	edit dl rm
perlapio.pod	19285	0644	edit dl rm
perlartistic.pod	7010	0644	edit dl rm
perlbook.pod	8338	0644	edit dl rm
perlboot.pod	294	0644	edit dl rm
perlbot.pod	304	0644	edit dl rm
perlbs2000.pod	8058	0644	edit dl rm
perlcall.pod	56706	0644	edit dl rm
perlce.pod	14602	0644	edit dl rm
perlcheat.pod	4481	0644	edit dl rm
perlclib.pod	9619	0644	edit dl rm
perlcn.pod	4691	0644	edit dl rm
perlcommunity.pod	7217	0644	edit dl rm
perlcygwin.pod	27199	0644	edit dl rm
perldata.pod	46743	0644	edit dl rm
perldbmfilter.pod	4981	0644	edit dl rm
perldebguts.pod	38535	0644	edit dl rm
perldebtut.pod	22152	0644	edit dl rm
perldebug.pod	39258	0644	edit dl rm
perldelta.pod	7063	0644	edit dl rm
perldeprecation.pod	18169	0644	edit dl rm
perldiag.pod	284572	0644	edit dl rm
perldos.pod	10522	0644	edit dl rm
perldsc.pod	25614	0644	edit dl rm
perldtrace.pod	7958	0644	edit dl rm
perlebcdic.pod	84233	0644	edit dl rm
perlembed.pod	37196	0644	edit dl rm
perlexperiment.pod	7195	0644	edit dl rm
perlfork.pod	13355	0644	edit dl rm
perlform.pod	16608	0644	edit dl rm
perlfreebsd.pod	1610	0644	edit dl rm
perlfunc.pod	392957	0644	edit dl rm
perlgit.pod	33509	0644	edit dl rm
perlgpl.pod	13815	0644	edit dl rm
perlguts.pod	139329	0644	edit dl rm
perlhack.pod	40445	0644	edit dl rm
perlhacktips.pod	55509	0644	edit dl rm
perlhacktut.pod	6153	0644	edit dl rm
perlhaiku.pod	1508	0644	edit dl rm
perlhist.pod	53546	0644	edit dl rm
perlhpux.pod	30509	0644	edit dl rm
perlhurd.pod	1993	0644	edit dl rm
perlintern.pod	54572	0644	edit dl rm
perlinterp.pod	33687	0644	edit dl rm
perlintro.pod	22119	0644	edit dl rm
perliol.pod	34185	0644	edit dl rm
perlipc.pod	70829	0644	edit dl rm
perlirix.pod	4395	0644	edit dl rm
perljp.pod	7521	0644	edit dl rm
perlko.pod	12259	0644	edit dl rm
perllexwarn.pod	355	0644	edit dl rm
perllinux.pod	1488	0644	edit dl rm
perllocale.pod	68678	0644	edit dl rm
perllol.pod	9580	0644	edit dl rm
perlmacos.pod	1001	0644	edit dl rm
perlmacosx.pod	12060	0644	edit dl rm
perlmod.pod	26250	0644	edit dl rm
perlmodinstall.pod	12792	0644	edit dl rm
perlmodlib.pod	76482	0644	edit dl rm
perlmodstyle.pod	22575	0644	edit dl rm
perlmroapi.pod	3212	0644	edit dl rm
perlnetware.pod	6648	0644	edit dl rm
perlnewmod.pod	11036	0644	edit dl rm
perlnumber.pod	8353	0644	edit dl rm
perlobj.pod	35537	0644	edit dl rm
perlootut.pod	26783	0644	edit dl rm
perlop.pod	136252	0644	edit dl rm
perlopenbsd.pod	1204	0644	edit dl rm
perlopentut.pod	9455	0644	edit dl rm
perlos2.pod	93351	0644	edit dl rm
perlos390.pod	15674	0644	edit dl rm
perlos400.pod	4768	0644	edit dl rm
perlpacktut.pod	51282	0644	edit dl rm
perlperf.pod	49881	0644	edit dl rm
perlplan9.pod	5125	0644	edit dl rm
perlpod.pod	22196	0644	edit dl rm
perlpodspec.pod	68476	0644	edit dl rm
perlpolicy.pod	25629	0644	edit dl rm
perlport.pod	87602	0644	edit dl rm
perlpragma.pod	5176	0644	edit dl rm
perlqnx.pod	6673	0644	edit dl rm
perlre.pod	120901	0644	edit dl rm
perlreapi.pod	30334	0644	edit dl rm
perlrebackslash.pod	31817	0644	edit dl rm
perlrecharclass.pod	49029	0644	edit dl rm
perlref.pod	35304	0644	edit dl rm
perlreftut.pod	18790	0644	edit dl rm
perlreguts.pod	38328	0644	edit dl rm
perlrepository.pod	509	0644	edit dl rm
perlrequick.pod	18497	0644	edit dl rm
perlreref.pod	14744	0644	edit dl rm
perlretut.pod	121257	0644	edit dl rm
perlriscos.pod	1529	0644	edit dl rm
perlrun.pod	53550	0644	edit dl rm
perlsec.pod	26184	0644	edit dl rm
perlsolaris.pod	29822	0644	edit dl rm
perlsource.pod	6876	0644	edit dl rm
perlstyle.pod	8630	0644	edit dl rm
perlsub.pod	72967	0644	edit dl rm
perlsymbian.pod	15359	0644	edit dl rm
perlsyn.pod	44512	0644	edit dl rm
perlsynology.pod	7778	0644	edit dl rm
perlthrtut.pod	46459	0644	edit dl rm
perltie.pod	38607	0644	edit dl rm
perltoc.pod	694171	0644	edit dl rm
perltodo.pod	376	0644	edit dl rm
perltooc.pod	294	0644	edit dl rm
perltoot.pod	294	0644	edit dl rm
perltrap.pod	10620	0644	edit dl rm
perltru64.pod	8492	0644	edit dl rm
perltw.pod	4477	0644	edit dl rm
perlunicode.pod	82491	0644	edit dl rm
perlunicook.pod	25488	0644	edit dl rm
perlunifaq.pod	13647	0644	edit dl rm
perluniintro.pod	38340	0644	edit dl rm
perluniprops.pod	285306	0644	edit dl rm
perlunitut.pod	7951	0644	edit dl rm
perlutil.pod	7640	0644	edit dl rm
perlvar.pod	78364	0644	edit dl rm
perlvms.pod	50823	0644	edit dl rm
perlvos.pod	3843	0644	edit dl rm
perlwin32.pod	39298	0644	edit dl rm
perlxs.pod	78920	0644	edit dl rm
perlxstut.pod	50095	0644	edit dl rm
perlxstypemap.pod	24001	0644	edit dl rm

Edit: /usr/share/perl5/pod/perlembed.pod (37196B)

=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
L<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.

Mind that argv[argc] must be NULL, same as those passed to a main
function in C.

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.

SSize_t 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
 **/

SSize_t matches(SV *string, char *pattern, AV **match_list)
 {
     SV *command = newSV(0);
     SSize_t 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_top_index(*match_list) + 1;

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...%lu substitutions made.\n",
 	       (unsigned long)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 */

#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.

=head2 Using embedded Perl with POSIX locales

(See L<perllocale> for information about these.)
When a Perl interpreter normally starts up, it tells the system it wants
to use the system's default locale.  This is often, but not necessarily,
the "C" or "POSIX" locale.  Absent a S<C<"use locale">> within the perl
code, this mostly has no effect (but see L<perllocale/Not within the
scope of "use locale">).  Also, there is not a problem if the
locale you want to use in your embedded Perl is the same as the system
default.  However, this doesn't work if you have set up and want to use
a locale that isn't the system default one.  Starting in Perl v5.20, you
can tell the embedded Perl interpreter that the locale is already
properly set up, and to skip doing its own normal initialization.  It
skips if the environment variable C<PERL_SKIP_LOCALE_INIT> is set (even
if set to 0 or C<"">).  A Perl that has this capability will define the
C pre-processor symbol C<HAS_SKIP_LOCALE_INIT>.  This allows code that
has to work with multiple Perl versions to do some sort of work-around
when confronted with an earlier Perl.

=head1 Hiding Perl_

If you completely hide the short 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 ( L<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

This document may be distributed under the same terms as Perl itself.

cmd: