There's one example in each of the eight sections:
Adding a Perl interpreter to your C program
Calling a Perl subroutine from your C program
Evaluating a Perl statement from your C program
Performing Perl pattern matches and substitutions from your C program
Fiddling with the Perl stack from your C program
Maintaining a persistent interpreter
Maintaining multiple interpreter instances
Using Perl modules, which themselves use C libraries, from your C program
This documentation is Unix specific; if you have information about how to embed Perl on other platforms, please send e-mail to <orwant@tpj.com>.
Also, every C program that uses Perl must link in the 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 ( /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 lib directory.)
When you use Perl from C, your C program will--usually--allocate, ``run'', and deallocate a 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 EXTERN.h and 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, 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 5.00305, 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 perl -V command and pay special attention to the ``cc'' and ``ccflags''
information.
You'll have to choose the appropriate compiler (cc, gcc, et al.) for your machine: perl -MConfig -e 'print $Config{cc}' will tell you what to use.
You'll also have to choose the appropriate library directory (/usr/local/lib/...) for your machine. If your compiler complains that certain functions are
undefined, or that it can't locate
-lperl, then you need to change the path following the -L. If it complains that it can't find EXTERN.h and perl.h, you need to change the path following the -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 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 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::Embed. (If this documentation came from your Perl distribution, then you're running 5.004 or better and you already have it.)
The 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.
#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)
{
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
perl_run(my_perl);
perl_destruct(my_perl);
perl_free(my_perl);
}
Notice that we don't use the env pointer. Normally handed to
perl_parse as its final argument, env here is replaced by
NULL, which means that the current environment will be used.
Now compile this program (I'll call it 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 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
or
% 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 argv[1] before calling perl_run().
That's shown below, in a program I'll call showtime.c.
#include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;
int main(int argc, char **argv, char **env)
{
char *args[] = { NULL };
my_perl = perl_alloc();
perl_construct(my_perl);
perl_parse(my_perl, NULL, argc, argv, NULL);
/*** skipping perl_run() ***/
perl_call_argv("showtime", G_DISCARD | G_NOARGS, args);
perl_destruct(my_perl);
perl_free(my_perl);
}
where showtime is a Perl subroutine that takes no arguments (that's the G_NOARGS) and for which I'll ignore the return value (that's the G_DISCARD). Those flags, and others, are discussed in the perlcall manpage.
I'll define the showtime subroutine in a file called 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 perl_run, but in general it's considered good practice to ensure proper
initialization of library code, including execution of all object DESTROY methods and package END {} blocks.
If you want to pass arguments to the Perl subroutine, you can add strings
to the NULL-terminated args list passed to
perl_call_argv. For other data types, or to examine return values, you'll need to
manipulate the Perl stack. That's demonstrated in the last section of this
document: Fiddling with the Perl stack from your C program.
Arguably, this is the only routine you'll ever need to execute snippets of Perl code from within your C program. Your string can be as long as you wish; it can contain multiple statements; it can employ use, require and do to include external Perl files.
Our perl_eval() lets us evaluate individual Perl strings, and then extract variables for coercion into
C types. The following program,
string.c, executes three Perl strings, extracting an int from the first, a float from the second, and a char * from the third.
#include <EXTERN.h> #include <perl.h>
static PerlInterpreter *my_perl;
I32 perl_eval(char *string)
{
return perl_eval_sv(newSVpv(string,0), G_DISCARD);
}
main (int argc, char **argv, char **env)
{
char *embedding[] = { "", "-e", "0" };
STRLEN length;
my_perl = perl_alloc();
perl_construct( my_perl );
perl_parse(my_perl, NULL, 3, embedding, NULL);
perl_run(my_perl);
/** Treat $a as an integer **/
perl_eval("$a = 3; $a **= 2");
printf("a = %d\n", SvIV(perl_get_sv("a", FALSE)));
/** Treat $a as a float **/
perl_eval("$a = 3.14; $a **= 2");
printf("a = %f\n", SvNV(perl_get_sv("a", FALSE)));
/** Treat $a as a string **/
perl_eval("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a); ");
printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), length));
perl_destruct(my_perl);
perl_free(my_perl);
}
All of those strange functions with sv in their names help convert Perl scalars to C types. They're described in the perlguts manpage.
If you compile and run string.c, you'll see the results of using
SvIV() to create an int, SvNV() to create a float, and
SvPV() to create a string:
a = 9 a = 9.859600 a = Just Another Perl Hacker
char match(char *string, char *pattern);
Given a string and a pattern (e.g., m/clasp/ or /\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(char *string[], char *pattern);
Given a pointer to a string and an =~ operation (e.g.,
s/bob/robert/g or tr[A-Z][a-z]), substitute modifies the string according to the operation,
returning the number of substitutions made.
int matches(char *string, char *pattern, char **matches[]);
Given a string, a pattern, and a pointer to an empty array of strings,
matches evaluates $string =~ $pattern in an array context, and fills in matches with the array elements (allocating memory as it does so), returning the
number of matches found.
Here's a sample program, match.c, that uses all three (long lines have been wrapped here):
#include <EXTERN.h> #include <perl.h>
static PerlInterpreter *my_perl;
I32 perl_eval(char *string)
{
return perl_eval_sv(newSVpv(string,0), G_DISCARD);
}
/** match(string, pattern)
**
** Used for matches in a scalar context.
**
** Returns 1 if the match was successful; 0 otherwise.
**/
char match(char *string, char *pattern)
{
char *command;
command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 37);
sprintf(command, "$string = '%s'; $return = $string =~ %s",
string, pattern);
perl_eval(command);
free(command);
return SvIV(perl_get_sv("return", FALSE));
}
/** substitute(string, pattern)
**
** Used for =~ operations that modify their left-hand side (s/// and tr///)
**
** Returns the number of successful matches, and
** modifies the input string if there were any.
**/
int substitute(char *string[], char *pattern)
{
char *command;
STRLEN length;
command = malloc(sizeof(char) * strlen(*string) + strlen(pattern) + 35);
sprintf(command, "$string = '%s'; $ret = ($string =~ %s)",
*string, pattern);
perl_eval(command);
free(command);
*string = SvPV(perl_get_sv("string", FALSE), length);
return SvIV(perl_get_sv("ret", FALSE));
}
/** matches(string, pattern, matches)
**
** Used for matches in an array context.
**
** Returns the number of matches,
** and fills in **matches with the matching substrings (allocates memory!)
**/
int matches(char *string, char *pattern, char **match_list[])
{
char *command;
SV *current_match;
AV *array;
I32 num_matches;
STRLEN length;
int i;
command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 38);
sprintf(command, "$string = '%s'; @array = ($string =~ %s)",
string, pattern);
perl_eval(command);
free(command);
array = perl_get_av("array", FALSE);
num_matches = av_len(array) + 1; /** assume $[ is 0 **/
*match_list = (char **) malloc(sizeof(char *) * num_matches);
for (i = 0; i <= num_matches; i++) {
current_match = av_shift(array);
(*match_list)[i] = SvPV(current_match, length);
}
return num_matches;
}
main (int argc, char **argv, char **env)
{
char *embedding[] = { "", "-e", "0" };
char *text, **match_list;
int num_matches, i;
int j;
my_perl = perl_alloc();
perl_construct( my_perl );
perl_parse(my_perl, NULL, 3, embedding, NULL);
perl_run(my_perl);
text = (char *) malloc(sizeof(char) * 486); /** A long string follows! **/
sprintf(text, "%s", "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", match_list[i]);
printf("\n");
for (i = 0; i < num_matches; i++) {
free(match_list[i]);
}
free(match_list);
/** 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", text);
}
/** Attempt a substitution **/
if (!substitute(&text, "s/Perl/C/")) {
printf("substitute: s/Perl/C...No substitution made.\n\n");
}
free(text);
perl_destruct(my_perl);
perl_free(my_perl);
}
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.
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 the perlguts manpage.
Then you'll need to know how to manipulate the Perl stack. That's described in the perlcall manpage.
Once you've understood those, embedding Perl in C is easy.
Because C has no built-in 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 pow() function). First I'll create a stub exponentiation function in power.pl:
sub expo {
my ($a, $b) = @_;
return $a ** $b;
}
Now I'll create a C program, power.c, with a function PerlPower() that contains all the perlguts necessary to push the two arguments into 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 */
perl_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[2];
my_perl = perl_alloc();
perl_construct( my_perl );
my_argv[1] = (char *) malloc(10);
sprintf(my_argv[1], "power.pl");
perl_parse(my_perl, NULL, argc, my_argv, NULL);
perl_run(my_perl);
PerlPower(3, 4); /*** Compute 3 ** 4 ***/
perl_destruct(my_perl);
perl_free(my_perl);
}
Compile and run:
% cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
% power
3 to the 4th power is 81.
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 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 perl_parse, compiled into a newly constructed interpreter, and subsequently cleaned out with 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 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 perl_call_argv, We'll call the subroutine Embed::Persistent::eval_file which lives in the file 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 AUTOLOADed 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 my whenever possible.
package Embed::Persistent;
#persistent.pl
use strict;
use vars '%Cache';
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;
}
#borrowed from Safe.pm
sub delete_package {
my $pkg = shift;
my ($stem, $leaf);
no strict 'refs';
$pkg = "main::$pkg\::"; # expand to full symbol table name
($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
my $stem_symtab = *{$stem}{HASH};
delete $stem_symtab->{$leaf};
}
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, $/;
}
1;
__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
static PerlInterpreter *perl = NULL;
int
main(int argc, char **argv, char **env)
{
char *embedding[] = { "", "persistent.pl" };
char *args[] = { "", DO_CLEAN, NULL };
char filename [1024];
int exitstatus = 0;
if((perl = perl_alloc()) == NULL) {
fprintf(stderr, "no memory!");
exit(1);
}
perl_construct(perl);
exitstatus = perl_parse(perl, NULL, 2, embedding, NULL);
if(!exitstatus) {
exitstatus = perl_run(perl);
while(printf("Enter file name: ") && gets(filename)) {
/* call the subroutine, passing it the filename as an argument */
args[0] = filename;
perl_call_argv("Embed::Persistent::eval_file",
G_DISCARD | G_EVAL, args);
/* check $@ */
if(SvTRUE(GvSV(errgv)))
fprintf(stderr, "eval error: %s\n", SvPV(GvSV(errgv),na));
}
}
perl_destruct_level = 0;
perl_destruct(perl);
perl_free(perl);
exit(exitstatus);
}
Now compile:
% cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
Here's a 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
The program must take care to ensure that this takes place before
the next interpreter is constructed. By default, the global variable
perl_destruct_level is set to , since extra cleaning isn't needed when a program has only one
interpreter.
Setting perl_destruct_level to 1 makes everything squeaky clean:
perl_destruct_level = 1;
while(1) {
...
/* reset global variables here with perl_destruct_level = 1 */
perl_construct(my_perl);
...
/* clean and reset _everything_ during perl_destruct */
perl_destruct(my_perl);
perl_free(my_perl);
...
/* let's go do it again! */
}
When perl_destruct() is called, the interpreter's syntax parse tree and symbol tables are cleaned up, and global variables are reset.
Now suppose we have more than one interpreter instance running at the same
time. This is feasible, but only if you used the
-DMULTIPLICITY flag when building Perl. By default, that sets
perl_destruct_level to 1.
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 = perl_alloc(),
*two_perl = perl_alloc();
char *one_args[] = { "one_perl", SAY_HELLO };
char *two_args[] = { "two_perl", SAY_HELLO };
perl_construct(one_perl);
perl_construct(two_perl);
perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
perl_run(one_perl);
perl_run(two_perl);
perl_destruct(one_perl);
perl_destruct(two_perl);
perl_free(one_perl);
perl_free(two_perl);
}
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
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 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 perlmain.c to see how Perl does this:
#ifdef __cplusplus # define EXTERN_C extern "C" #else # define EXTERN_C extern #endif
static void xs_init _((void));
EXTERN_C void boot_DynaLoader _((CV* cv)); EXTERN_C void boot_Socket _((CV* cv));
EXTERN_C void
xs_init()
{
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 Module::bootstrap() and is invoked when you say use Module. In turn, this hooks into an XSUB, boot_Module, which creates a Perl counterpart for each of the extension's XSUBs. Don't worry about this part; leave that to the xsubpp and extension authors. If your extension is dynamically loaded, DynaLoader creates 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 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"'
ExtUtils::Embed can also automate writing the 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 the perlxs manpage and the perlguts manpage for more details.
Check out Doug's article on embedding in Volume 1, Issue 4 of The Perl Journal. Info about TPJ is available from http://tpj.com.
February 1, 1997
Some of this material is excerpted from Jon Orwant's book: Perl 5 Interactive, Waite Group Press, 1996 (ISBN 1-57169-064-6) and appears courtesy of Waite Group Press.
Although destined for release with the standard Perl distribution, this document is not public domain, nor is any of Perl and its documentation. Permission is granted to freely distribute verbatim copies of this document provided that no modifications outside of formatting be made, and that this notice remain intact. You are permitted and encouraged to use its code and derivatives thereof in your own source code for fun or for profit as you see fit.