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1=head1 NAME
2
cb1a09d0 3perlembed - how to embed perl in your C program
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4
5=head1 DESCRIPTION
6
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7=head2 PREAMBLE
8
9Do you want to:
10
11=over 5
12
96dbc785 13=item B<Use C from Perl?>
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14
15Read L<perlcall> and L<perlxs>.
16
54310121 17=item B<Use a Unix program from Perl?>
cb1a09d0 18
5f05dabc 19Read about back-quotes and about C<system> and C<exec> in L<perlfunc>.
cb1a09d0 20
96dbc785 21=item B<Use Perl from Perl?>
cb1a09d0 22
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23Read about L<perlfunc/do> and L<perlfunc/eval> and L<perlfunc/require>
24and L<perlfunc/use>.
cb1a09d0 25
96dbc785 26=item B<Use C from C?>
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27
28Rethink your design.
29
96dbc785 30=item B<Use Perl from C?>
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31
32Read on...
33
34=back
35
36=head2 ROADMAP
37
38L<Compiling your C program>
39
a6006777 40There's one example in each of the eight sections:
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41
42L<Adding a Perl interpreter to your C program>
43
44L<Calling a Perl subroutine from your C program>
45
46L<Evaluating a Perl statement from your C program>
47
48L<Performing Perl pattern matches and substitutions from your C program>
49
50L<Fiddling with the Perl stack from your C program>
51
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52L<Maintaining a persistent interpreter>
53
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54L<Maintaining multiple interpreter instances>
55
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56L<Using Perl modules, which themselves use C libraries, from your C program>
57
8a7dc658 58This documentation is Unix specific; if you have information about how
9607fc9c 59to embed Perl on other platforms, please send e-mail to <F<orwant@tpj.com>>.
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60
61=head2 Compiling your C program
62
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63If you have trouble compiling the scripts in this documentation,
64you're not alone. The cardinal rule: COMPILE THE PROGRAMS IN EXACTLY
65THE SAME WAY THAT YOUR PERL WAS COMPILED. (Sorry for yelling.)
cb1a09d0 66
8a7dc658 67Also, every C program that uses Perl must link in the I<perl library>.
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68What's that, you ask? Perl is itself written in C; the perl library
69is the collection of compiled C programs that were used to create your
70perl executable (I</usr/bin/perl> or equivalent). (Corollary: you
71can't use Perl from your C program unless Perl has been compiled on
72your machine, or installed properly--that's why you shouldn't blithely
73copy Perl executables from machine to machine without also copying the
74I<lib> directory.)
75
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76When you use Perl from C, your C program will--usually--allocate,
77"run", and deallocate a I<PerlInterpreter> object, which is defined by
78the perl library.
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79
80If your copy of Perl is recent enough to contain this documentation
a6006777 81(version 5.002 or later), then the perl library (and I<EXTERN.h> and
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82I<perl.h>, which you'll also need) will reside in a directory
83that looks like this:
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84
85 /usr/local/lib/perl5/your_architecture_here/CORE
86
87or perhaps just
88
89 /usr/local/lib/perl5/CORE
90
91or maybe something like
92
93 /usr/opt/perl5/CORE
94
95Execute this statement for a hint about where to find CORE:
96
96dbc785 97 perl -MConfig -e 'print $Config{archlib}'
cb1a09d0 98
54310121 99Here's how you'd compile the example in the next section,
8a7dc658 100L<Adding a Perl interpreter to your C program>, on my Linux box:
cb1a09d0 101
54310121 102 % gcc -O2 -Dbool=char -DHAS_BOOL -I/usr/local/include
8a7dc658 103 -I/usr/local/lib/perl5/i586-linux/5.003/CORE
54310121 104 -L/usr/local/lib/perl5/i586-linux/5.003/CORE
8a7dc658 105 -o interp interp.c -lperl -lm
cb1a09d0 106
54310121 107(That's all one line.) On my DEC Alpha running 5.003_05, the incantation
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108is a bit different:
109
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110 % cc -O2 -Olimit 2900 -DSTANDARD_C -I/usr/local/include
111 -I/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE
112 -L/usr/local/lib/perl5/alpha-dec_osf/5.00305/CORE -L/usr/local/lib
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113 -D__LANGUAGE_C__ -D_NO_PROTO -o interp interp.c -lperl -lm
114
115How can you figure out what to add? Assuming your Perl is post-5.001,
116execute a C<perl -V> command and pay special attention to the "cc" and
54310121 117"ccflags" information.
8a7dc658 118
54310121 119You'll have to choose the appropriate compiler (I<cc>, I<gcc>, et al.) for
8a7dc658 120your machine: C<perl -MConfig -e 'print $Config{cc}'> will tell you what
54310121 121to use.
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122
123You'll also have to choose the appropriate library directory
124(I</usr/local/lib/...>) for your machine. If your compiler complains
125that certain functions are undefined, or that it can't locate
126I<-lperl>, then you need to change the path following the C<-L>. If it
127complains that it can't find I<EXTERN.h> and I<perl.h>, you need to
128change the path following the C<-I>.
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129
130You may have to add extra libraries as well. Which ones?
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131Perhaps those printed by
132
133 perl -MConfig -e 'print $Config{libs}'
134
54310121 135Provided your perl binary was properly configured and installed the
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136B<ExtUtils::Embed> module will determine all of this information for
137you:
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138
139 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
140
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141If the B<ExtUtils::Embed> module isn't part of your Perl distribution,
142you can retrieve it from
143http://www.perl.com/perl/CPAN/modules/by-module/ExtUtils::Embed. (If
144this documentation came from your Perl distribution, then you're
145running 5.004 or better and you already have it.)
96dbc785 146
8a7dc658 147The B<ExtUtils::Embed> kit on CPAN also contains all source code for
54310121 148the examples in this document, tests, additional examples and other
8a7dc658 149information you may find useful.
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150
151=head2 Adding a Perl interpreter to your C program
152
153In a sense, perl (the C program) is a good example of embedding Perl
154(the language), so I'll demonstrate embedding with I<miniperlmain.c>,
54310121 155from the source distribution. Here's a bastardized, nonportable
8a7dc658 156version of I<miniperlmain.c> containing the essentials of embedding:
cb1a09d0 157
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158 #include <EXTERN.h> /* from the Perl distribution */
159 #include <perl.h> /* from the Perl distribution */
96dbc785 160
cb1a09d0 161 static PerlInterpreter *my_perl; /*** The Perl interpreter ***/
96dbc785 162
c07a80fd 163 int main(int argc, char **argv, char **env)
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164 {
165 my_perl = perl_alloc();
166 perl_construct(my_perl);
96dbc785 167 perl_parse(my_perl, NULL, argc, argv, (char **)NULL);
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168 perl_run(my_perl);
169 perl_destruct(my_perl);
170 perl_free(my_perl);
171 }
172
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173Notice that we don't use the C<env> pointer. Normally handed to
174C<perl_parse> as its final argument, C<env> here is replaced by
175C<NULL>, which means that the current environment will be used.
96dbc785 176
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177Now compile this program (I'll call it I<interp.c>) into an executable:
178
96dbc785 179 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
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180
181After a successful compilation, you'll be able to use I<interp> just
182like perl itself:
183
184 % interp
185 print "Pretty Good Perl \n";
186 print "10890 - 9801 is ", 10890 - 9801;
187 <CTRL-D>
188 Pretty Good Perl
189 10890 - 9801 is 1089
190
191or
192
193 % interp -e 'printf("%x", 3735928559)'
194 deadbeef
195
196You can also read and execute Perl statements from a file while in the
197midst of your C program, by placing the filename in I<argv[1]> before
96dbc785 198calling I<perl_run()>.
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199
200=head2 Calling a Perl subroutine from your C program
201
8ebc5c01 202To call individual Perl subroutines, you can use any of the B<perl_call_*>
54310121 203functions documented in the L<perlcall> manpage.
8ebc5c01 204In this example we'll use I<perl_call_argv>.
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205
206That's shown below, in a program I'll call I<showtime.c>.
207
cb1a09d0 208 #include <EXTERN.h>
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209 #include <perl.h>
210
211 static PerlInterpreter *my_perl;
212
c07a80fd 213 int main(int argc, char **argv, char **env)
cb1a09d0 214 {
8ebc5c01 215 char *args[] = { NULL };
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216 my_perl = perl_alloc();
217 perl_construct(my_perl);
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218
219 perl_parse(my_perl, NULL, argc, argv, NULL);
220
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221 /*** skipping perl_run() ***/
222
223 perl_call_argv("showtime", G_DISCARD | G_NOARGS, args);
224
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225 perl_destruct(my_perl);
226 perl_free(my_perl);
227 }
228
229where I<showtime> is a Perl subroutine that takes no arguments (that's the
96dbc785 230I<G_NOARGS>) and for which I'll ignore the return value (that's the
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231I<G_DISCARD>). Those flags, and others, are discussed in L<perlcall>.
232
233I'll define the I<showtime> subroutine in a file called I<showtime.pl>:
234
235 print "I shan't be printed.";
96dbc785 236
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237 sub showtime {
238 print time;
239 }
240
241Simple enough. Now compile and run:
242
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243 % cc -o showtime showtime.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
244
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245 % showtime showtime.pl
246 818284590
247
248yielding the number of seconds that elapsed between January 1, 1970
8a7dc658 249(the beginning of the Unix epoch), and the moment I began writing this
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250sentence.
251
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252In this particular case we don't have to call I<perl_run>, but in
253general it's considered good practice to ensure proper initialization
254of library code, including execution of all object C<DESTROY> methods
255and package C<END {}> blocks.
8ebc5c01 256
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257If you want to pass arguments to the Perl subroutine, you can add
258strings to the C<NULL>-terminated C<args> list passed to
259I<perl_call_argv>. For other data types, or to examine return values,
260you'll need to manipulate the Perl stack. That's demonstrated in the
261last section of this document: L<Fiddling with the Perl stack from
262your C program>.
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263
264=head2 Evaluating a Perl statement from your C program
265
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266Perl provides two API functions to evaluate pieces of Perl code.
267These are L<perlguts/perl_eval_sv()> and L<perlguts/perl_eval_pv()>.
268
269Arguably, these are the only routines you'll ever need to execute
270snippets of Perl code from within your C program. Your code can be
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271as long as you wish; it can contain multiple statements; it can employ
272L<perlfunc/use>, L<perlfunc/require> and L<perlfunc/do> to include
273external Perl files.
cb1a09d0 274
137443ea 275I<perl_eval_pv()> lets us evaluate individual Perl strings, and then
96dbc785 276extract variables for coercion into C types. The following program,
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277I<string.c>, executes three Perl strings, extracting an C<int> from
278the first, a C<float> from the second, and a C<char *> from the third.
279
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280 #include <EXTERN.h>
281 #include <perl.h>
137443ea 282
cb1a09d0 283 static PerlInterpreter *my_perl;
137443ea 284
c07a80fd 285 main (int argc, char **argv, char **env)
cb1a09d0 286 {
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287 char *embedding[] = { "", "-e", "0" };
288
289 my_perl = perl_alloc();
290 perl_construct( my_perl );
291
292 perl_parse(my_perl, NULL, 3, embedding, NULL);
293 perl_run(my_perl);
294
295 /** Treat $a as an integer **/
296 perl_eval_pv("$a = 3; $a **= 2", TRUE);
297 printf("a = %d\n", SvIV(perl_get_sv("a", FALSE)));
298
299 /** Treat $a as a float **/
300 perl_eval_pv("$a = 3.14; $a **= 2", TRUE);
301 printf("a = %f\n", SvNV(perl_get_sv("a", FALSE)));
302
303 /** Treat $a as a string **/
304 perl_eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
305 printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), na));
306
307 perl_destruct(my_perl);
308 perl_free(my_perl);
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309 }
310
311All of those strange functions with I<sv> in their names help convert Perl scalars to C types. They're described in L<perlguts>.
312
313If you compile and run I<string.c>, you'll see the results of using
314I<SvIV()> to create an C<int>, I<SvNV()> to create a C<float>, and
315I<SvPV()> to create a string:
316
317 a = 9
318 a = 9.859600
319 a = Just Another Perl Hacker
320
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321In the example above, we've created a global variable to temporarily
322store the computed value of our eval'd expression. It is also
323possible and in most cases a better strategy to fetch the return value
137443ea 324from L<perl_eval_pv> instead. Example:
8f183262 325
8f183262 326 ...
137443ea 327 SV *val = perl_eval_pv("reverse 'rekcaH lreP rehtonA tsuJ'", TRUE);
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328 printf("%s\n", SvPV(val,na));
329 ...
330
331This way, we avoid namespace pollution by not creating global
332variables and we've simplified our code as well.
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333
334=head2 Performing Perl pattern matches and substitutions from your C program
335
137443ea 336The I<perl_eval_pv()> function lets us evaluate strings of Perl code, so we can
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337define some functions that use it to "specialize" in matches and
338substitutions: I<match()>, I<substitute()>, and I<matches()>.
339
96dbc785 340 char match(char *string, char *pattern);
cb1a09d0 341
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342Given a string and a pattern (e.g., C<m/clasp/> or C</\b\w*\b/>, which
343in your C program might appear as "/\\b\\w*\\b/"), match()
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344returns 1 if the string matches the pattern and 0 otherwise.
345
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346 int substitute(char *string[], char *pattern);
347
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348Given a pointer to a string and an C<=~> operation (e.g.,
349C<s/bob/robert/g> or C<tr[A-Z][a-z]>), substitute() modifies the string
350according to the operation, returning the number of substitutions
351made.
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352
353 int matches(char *string, char *pattern, char **matches[]);
354
355Given a string, a pattern, and a pointer to an empty array of strings,
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356matches() evaluates C<$string =~ $pattern> in an array context, and
357fills in I<matches> with the array elements (allocating memory as it
358does so), returning the number of matches found.
cb1a09d0 359
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360Here's a sample program, I<match.c>, that uses all three (long lines have
361been wrapped here):
cb1a09d0 362
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363 #include <EXTERN.h>
364 #include <perl.h>
8a7dc658 365
cb1a09d0 366 static PerlInterpreter *my_perl;
137443ea 367
cb1a09d0 368 /** match(string, pattern)
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369 **
370 ** Used for matches in a scalar context.
371 **
372 ** Returns 1 if the match was successful; 0 otherwise.
373 **/
374 char match(char *string, char *pattern)
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375 {
376 char *command;
377 command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 37);
96dbc785 378 sprintf(command, "$string = '%s'; $return = $string =~ %s",
8ebc5c01 379 string, pattern);
137443ea 380 perl_eval_pv(command, TRUE);
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381 free(command);
382 return SvIV(perl_get_sv("return", FALSE));
383 }
cb1a09d0 384 /** substitute(string, pattern)
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385 **
386 ** Used for =~ operations that modify their left-hand side (s/// and tr///)
387 **
388 ** Returns the number of successful matches, and
389 ** modifies the input string if there were any.
390 **/
391 int substitute(char *string[], char *pattern)
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392 {
393 char *command;
394 STRLEN length;
395 command = malloc(sizeof(char) * strlen(*string) + strlen(pattern) + 35);
96dbc785 396 sprintf(command, "$string = '%s'; $ret = ($string =~ %s)",
8ebc5c01 397 *string, pattern);
137443ea 398 perl_eval_pv(command, TRUE);
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399 free(command);
400 *string = SvPV(perl_get_sv("string", FALSE), length);
401 return SvIV(perl_get_sv("ret", FALSE));
cb1a09d0 402 }
cb1a09d0 403 /** matches(string, pattern, matches)
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404 **
405 ** Used for matches in an array context.
406 **
407 ** Returns the number of matches,
408 ** and fills in **matches with the matching substrings (allocates memory!)
409 **/
410 int matches(char *string, char *pattern, char **match_list[])
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411 {
412 char *command;
413 SV *current_match;
414 AV *array;
415 I32 num_matches;
416 STRLEN length;
417 int i;
cb1a09d0 418 command = malloc(sizeof(char) * strlen(string) + strlen(pattern) + 38);
96dbc785 419 sprintf(command, "$string = '%s'; @array = ($string =~ %s)",
8ebc5c01 420 string, pattern);
137443ea 421 perl_eval_pv(command, TRUE);
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422 free(command);
423 array = perl_get_av("array", FALSE);
424 num_matches = av_len(array) + 1; /** assume $[ is 0 **/
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425 *match_list = (char **) malloc(sizeof(char *) * num_matches);
426 for (i = 0; i <= num_matches; i++) {
cb1a09d0 427 current_match = av_shift(array);
96dbc785 428 (*match_list)[i] = SvPV(current_match, length);
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429 }
430 return num_matches;
431 }
c07a80fd 432 main (int argc, char **argv, char **env)
cb1a09d0 433 {
a6006777 434 char *embedding[] = { "", "-e", "0" };
96dbc785 435 char *text, **match_list;
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436 int num_matches, i;
437 int j;
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438 my_perl = perl_alloc();
439 perl_construct( my_perl );
96dbc785 440 perl_parse(my_perl, NULL, 3, embedding, NULL);
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441 perl_run(my_perl);
442
cb1a09d0 443 text = (char *) malloc(sizeof(char) * 486); /** A long string follows! **/
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444 sprintf(text, "%s", "When he is at a convenience store and the bill \
445 comes to some amount like 76 cents, Maynard is aware that there is \
446 something he *should* do, something that will enable him to get back \
447 a quarter, but he has no idea *what*. He fumbles through his red \
448 squeezey changepurse and gives the boy three extra pennies with his \
449 dollar, hoping that he might luck into the correct amount. The boy \
450 gives him back two of his own pennies and then the big shiny quarter \
451 that is his prize. -RICHH");
452 if (match(text, "m/quarter/")) /** Does text contain 'quarter'? **/
453 printf("match: Text contains the word 'quarter'.\n\n");
454 else
455 printf("match: Text doesn't contain the word 'quarter'.\n\n");
456 if (match(text, "m/eighth/")) /** Does text contain 'eighth'? **/
457 printf("match: Text contains the word 'eighth'.\n\n");
458 else
459 printf("match: Text doesn't contain the word 'eighth'.\n\n");
460 /** Match all occurrences of /wi../ **/
461 num_matches = matches(text, "m/(wi..)/g", &match_list);
462 printf("matches: m/(wi..)/g found %d matches...\n", num_matches);
463 for (i = 0; i < num_matches; i++)
464 printf("match: %s\n", match_list[i]);
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465 printf("\n");
466 for (i = 0; i < num_matches; i++) {
96dbc785 467 free(match_list[i]);
cb1a09d0 468 }
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469 free(match_list);
470 /** Remove all vowels from text **/
471 num_matches = substitute(&text, "s/[aeiou]//gi");
cb1a09d0 472 if (num_matches) {
96dbc785 473 printf("substitute: s/[aeiou]//gi...%d substitutions made.\n",
8ebc5c01 474 num_matches);
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475 printf("Now text is: %s\n\n", text);
476 }
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477 /** Attempt a substitution **/
478 if (!substitute(&text, "s/Perl/C/")) {
479 printf("substitute: s/Perl/C...No substitution made.\n\n");
cb1a09d0 480 }
cb1a09d0 481 free(text);
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482 perl_destruct(my_perl);
483 perl_free(my_perl);
484 }
485
96dbc785 486which produces the output (again, long lines have been wrapped here)
cb1a09d0 487
8a7dc658 488 match: Text contains the word 'quarter'.
96dbc785 489
8a7dc658 490 match: Text doesn't contain the word 'eighth'.
96dbc785 491
8a7dc658 492 matches: m/(wi..)/g found 2 matches...
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493 match: will
494 match: with
96dbc785 495
8a7dc658 496 substitute: s/[aeiou]//gi...139 substitutions made.
54310121 497 Now text is: Whn h s t cnvnnc str nd th bll cms t sm mnt lk 76 cnts,
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498 Mynrd s wr tht thr s smthng h *shld* d, smthng tht wll nbl hm t gt bck
499 qrtr, bt h hs n d *wht*. H fmbls thrgh hs rd sqzy chngprs nd gvs th by
500 thr xtr pnns wth hs dllr, hpng tht h mght lck nt th crrct mnt. Th by gvs
501 hm bck tw f hs wn pnns nd thn th bg shny qrtr tht s hs prz. -RCHH
502
8a7dc658 503 substitute: s/Perl/C...No substitution made.
96dbc785 504
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505=head2 Fiddling with the Perl stack from your C program
506
507When trying to explain stacks, most computer science textbooks mumble
508something about spring-loaded columns of cafeteria plates: the last
509thing you pushed on the stack is the first thing you pop off. That'll
510do for our purposes: your C program will push some arguments onto "the Perl
511stack", shut its eyes while some magic happens, and then pop the
512results--the return value of your Perl subroutine--off the stack.
96dbc785 513
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514First you'll need to know how to convert between C types and Perl
515types, with newSViv() and sv_setnv() and newAV() and all their
516friends. They're described in L<perlguts>.
517
518Then you'll need to know how to manipulate the Perl stack. That's
519described in L<perlcall>.
520
96dbc785 521Once you've understood those, embedding Perl in C is easy.
cb1a09d0 522
54310121 523Because C has no builtin function for integer exponentiation, let's
cb1a09d0 524make Perl's ** operator available to it (this is less useful than it
5f05dabc 525sounds, because Perl implements ** with C's I<pow()> function). First
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526I'll create a stub exponentiation function in I<power.pl>:
527
528 sub expo {
529 my ($a, $b) = @_;
530 return $a ** $b;
531 }
532
533Now I'll create a C program, I<power.c>, with a function
534I<PerlPower()> that contains all the perlguts necessary to push the
535two arguments into I<expo()> and to pop the return value out. Take a
536deep breath...
537
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538 #include <EXTERN.h>
539 #include <perl.h>
96dbc785 540
cb1a09d0 541 static PerlInterpreter *my_perl;
96dbc785 542
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543 static void
544 PerlPower(int a, int b)
545 {
546 dSP; /* initialize stack pointer */
547 ENTER; /* everything created after here */
548 SAVETMPS; /* ...is a temporary variable. */
549 PUSHMARK(sp); /* remember the stack pointer */
550 XPUSHs(sv_2mortal(newSViv(a))); /* push the base onto the stack */
551 XPUSHs(sv_2mortal(newSViv(b))); /* push the exponent onto stack */
552 PUTBACK; /* make local stack pointer global */
553 perl_call_pv("expo", G_SCALAR); /* call the function */
554 SPAGAIN; /* refresh stack pointer */
555 /* pop the return value from stack */
556 printf ("%d to the %dth power is %d.\n", a, b, POPi);
96dbc785 557 PUTBACK;
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558 FREETMPS; /* free that return value */
559 LEAVE; /* ...and the XPUSHed "mortal" args.*/
560 }
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561
562 int main (int argc, char **argv, char **env)
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563 {
564 char *my_argv[2];
96dbc785 565
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566 my_perl = perl_alloc();
567 perl_construct( my_perl );
96dbc785 568
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569 my_argv[1] = (char *) malloc(10);
570 sprintf(my_argv[1], "power.pl");
96dbc785
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571
572 perl_parse(my_perl, NULL, argc, my_argv, NULL);
8ebc5c01 573 perl_run(my_perl);
96dbc785 574
cb1a09d0 575 PerlPower(3, 4); /*** Compute 3 ** 4 ***/
96dbc785 576
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577 perl_destruct(my_perl);
578 perl_free(my_perl);
579 }
96dbc785 580
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581
582
583Compile and run:
584
96dbc785
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585 % cc -o power power.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
586
587 % power
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588 3 to the 4th power is 81.
589
a6006777
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590=head2 Maintaining a persistent interpreter
591
8a7dc658
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592When developing interactive and/or potentially long-running
593applications, it's a good idea to maintain a persistent interpreter
594rather than allocating and constructing a new interpreter multiple
595times. The major reason is speed: since Perl will only be loaded into
54310121 596memory once.
8a7dc658
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597
598However, you have to be more cautious with namespace and variable
599scoping when using a persistent interpreter. In previous examples
600we've been using global variables in the default package C<main>. We
601knew exactly what code would be run, and assumed we could avoid
602variable collisions and outrageous symbol table growth.
603
604Let's say your application is a server that will occasionally run Perl
605code from some arbitrary file. Your server has no way of knowing what
606code it's going to run. Very dangerous.
607
608If the file is pulled in by C<perl_parse()>, compiled into a newly
609constructed interpreter, and subsequently cleaned out with
610C<perl_destruct()> afterwards, you're shielded from most namespace
611troubles.
612
613One way to avoid namespace collisions in this scenario is to translate
614the filename into a guaranteed-unique package name, and then compile
615the code into that package using L<perlfunc/eval>. In the example
616below, each file will only be compiled once. Or, the application
617might choose to clean out the symbol table associated with the file
618after it's no longer needed. Using L<perlcall/perl_call_argv>, We'll
619call the subroutine C<Embed::Persistent::eval_file> which lives in the
620file C<persistent.pl> and pass the filename and boolean cleanup/cache
a6006777
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621flag as arguments.
622
8a7dc658
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623Note that the process will continue to grow for each file that it
624uses. In addition, there might be C<AUTOLOAD>ed subroutines and other
625conditions that cause Perl's symbol table to grow. You might want to
626add some logic that keeps track of the process size, or restarts
627itself after a certain number of requests, to ensure that memory
628consumption is minimized. You'll also want to scope your variables
629with L<perlfunc/my> whenever possible.
a6006777 630
54310121 631
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632 package Embed::Persistent;
633 #persistent.pl
54310121 634
a6006777
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635 use strict;
636 use vars '%Cache';
54310121 637
a6006777
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638 sub valid_package_name {
639 my($string) = @_;
640 $string =~ s/([^A-Za-z0-9\/])/sprintf("_%2x",unpack("C",$1))/eg;
641 # second pass only for words starting with a digit
642 $string =~ s|/(\d)|sprintf("/_%2x",unpack("C",$1))|eg;
54310121 643
a6006777
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644 # Dress it up as a real package name
645 $string =~ s|/|::|g;
646 return "Embed" . $string;
647 }
54310121 648
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649 #borrowed from Safe.pm
650 sub delete_package {
651 my $pkg = shift;
652 my ($stem, $leaf);
54310121 653
a6006777 654 no strict 'refs';
8ebc5c01 655 $pkg = "main::$pkg\::"; # expand to full symbol table name
a6006777 656 ($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
54310121 657
a6006777 658 my $stem_symtab = *{$stem}{HASH};
54310121 659
a6006777
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660 delete $stem_symtab->{$leaf};
661 }
54310121 662
a6006777
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663 sub eval_file {
664 my($filename, $delete) = @_;
665 my $package = valid_package_name($filename);
666 my $mtime = -M $filename;
667 if(defined $Cache{$package}{mtime}
668 &&
54310121 669 $Cache{$package}{mtime} <= $mtime)
a6006777 670 {
54310121 671 # we have compiled this subroutine already,
8ebc5c01
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672 # it has not been updated on disk, nothing left to do
673 print STDERR "already compiled $package->handler\n";
a6006777
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674 }
675 else {
8ebc5c01
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676 local *FH;
677 open FH, $filename or die "open '$filename' $!";
678 local($/) = undef;
679 my $sub = <FH>;
680 close FH;
54310121 681
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682 #wrap the code into a subroutine inside our unique package
683 my $eval = qq{package $package; sub handler { $sub; }};
684 {
685 # hide our variables within this block
686 my($filename,$mtime,$package,$sub);
687 eval $eval;
688 }
689 die $@ if $@;
54310121 690
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691 #cache it unless we're cleaning out each time
692 $Cache{$package}{mtime} = $mtime unless $delete;
a6006777 693 }
54310121 694
a6006777
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695 eval {$package->handler;};
696 die $@ if $@;
54310121 697
a6006777 698 delete_package($package) if $delete;
54310121 699
a6006777
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700 #take a look if you want
701 #print Devel::Symdump->rnew($package)->as_string, $/;
702 }
54310121 703
a6006777 704 1;
54310121 705
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706 __END__
707
708 /* persistent.c */
54310121
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709 #include <EXTERN.h>
710 #include <perl.h>
711
a6006777
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712 /* 1 = clean out filename's symbol table after each request, 0 = don't */
713 #ifndef DO_CLEAN
714 #define DO_CLEAN 0
715 #endif
54310121 716
a6006777 717 static PerlInterpreter *perl = NULL;
54310121 718
a6006777
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719 int
720 main(int argc, char **argv, char **env)
721 {
722 char *embedding[] = { "", "persistent.pl" };
723 char *args[] = { "", DO_CLEAN, NULL };
724 char filename [1024];
725 int exitstatus = 0;
54310121 726
a6006777 727 if((perl = perl_alloc()) == NULL) {
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728 fprintf(stderr, "no memory!");
729 exit(1);
a6006777 730 }
54310121
PP
731 perl_construct(perl);
732
a6006777 733 exitstatus = perl_parse(perl, NULL, 2, embedding, NULL);
54310121
PP
734
735 if(!exitstatus) {
8ebc5c01 736 exitstatus = perl_run(perl);
54310121 737
8ebc5c01 738 while(printf("Enter file name: ") && gets(filename)) {
54310121 739
8ebc5c01
PP
740 /* call the subroutine, passing it the filename as an argument */
741 args[0] = filename;
54310121 742 perl_call_argv("Embed::Persistent::eval_file",
8ebc5c01 743 G_DISCARD | G_EVAL, args);
54310121 744
8ebc5c01 745 /* check $@ */
54310121 746 if(SvTRUE(GvSV(errgv)))
8ebc5c01
PP
747 fprintf(stderr, "eval error: %s\n", SvPV(GvSV(errgv),na));
748 }
a6006777 749 }
54310121 750
a6006777 751 perl_destruct_level = 0;
54310121
PP
752 perl_destruct(perl);
753 perl_free(perl);
a6006777
PP
754 exit(exitstatus);
755 }
756
a6006777
PP
757Now compile:
758
54310121 759 % cc -o persistent persistent.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
a6006777
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760
761Here's a example script file:
762
763 #test.pl
764 my $string = "hello";
765 foo($string);
766
767 sub foo {
768 print "foo says: @_\n";
769 }
770
771Now run:
772
773 % persistent
774 Enter file name: test.pl
775 foo says: hello
776 Enter file name: test.pl
777 already compiled Embed::test_2epl->handler
778 foo says: hello
779 Enter file name: ^C
780
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781=head2 Maintaining multiple interpreter instances
782
8a7dc658
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783Some rare applications will need to create more than one interpreter
784during a session. Such an application might sporadically decide to
54310121 785release any resources associated with the interpreter.
8a7dc658
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786
787The program must take care to ensure that this takes place I<before>
788the next interpreter is constructed. By default, the global variable
789C<perl_destruct_level> is set to C<0>, since extra cleaning isn't
790needed when a program has only one interpreter.
791
792Setting C<perl_destruct_level> to C<1> makes everything squeaky clean:
793
54310121 794 perl_destruct_level = 1;
8ebc5c01 795
8ebc5c01
PP
796 while(1) {
797 ...
798 /* reset global variables here with perl_destruct_level = 1 */
54310121 799 perl_construct(my_perl);
8ebc5c01
PP
800 ...
801 /* clean and reset _everything_ during perl_destruct */
54310121
PP
802 perl_destruct(my_perl);
803 perl_free(my_perl);
8ebc5c01
PP
804 ...
805 /* let's go do it again! */
806 }
807
54310121
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808When I<perl_destruct()> is called, the interpreter's syntax parse tree
809and symbol tables are cleaned up, and global variables are reset.
8ebc5c01 810
8a7dc658
JO
811Now suppose we have more than one interpreter instance running at the
812same time. This is feasible, but only if you used the
813C<-DMULTIPLICITY> flag when building Perl. By default, that sets
814C<perl_destruct_level> to C<1>.
8ebc5c01
PP
815
816Let's give it a try:
817
818
819 #include <EXTERN.h>
8a7dc658 820 #include <perl.h>
8ebc5c01
PP
821
822 /* we're going to embed two interpreters */
823 /* we're going to embed two interpreters */
824
8ebc5c01
PP
825 #define SAY_HELLO "-e", "print qq(Hi, I'm $^X\n)"
826
8ebc5c01
PP
827 int main(int argc, char **argv, char **env)
828 {
54310121 829 PerlInterpreter
8ebc5c01 830 *one_perl = perl_alloc(),
54310121 831 *two_perl = perl_alloc();
8ebc5c01
PP
832 char *one_args[] = { "one_perl", SAY_HELLO };
833 char *two_args[] = { "two_perl", SAY_HELLO };
834
835 perl_construct(one_perl);
836 perl_construct(two_perl);
837
838 perl_parse(one_perl, NULL, 3, one_args, (char **)NULL);
839 perl_parse(two_perl, NULL, 3, two_args, (char **)NULL);
840
841 perl_run(one_perl);
842 perl_run(two_perl);
843
844 perl_destruct(one_perl);
845 perl_destruct(two_perl);
846
847 perl_free(one_perl);
848 perl_free(two_perl);
849 }
850
851
852Compile as usual:
853
854 % cc -o multiplicity multiplicity.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
855
856Run it, Run it:
857
858 % multiplicity
859 Hi, I'm one_perl
860 Hi, I'm two_perl
861
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862=head2 Using Perl modules, which themselves use C libraries, from your C program
863
864If you've played with the examples above and tried to embed a script
865that I<use()>s a Perl module (such as I<Socket>) which itself uses a C or C++ library,
866this probably happened:
867
868
869 Can't load module Socket, dynamic loading not available in this perl.
870 (You may need to build a new perl executable which either supports
871 dynamic loading or has the Socket module statically linked into it.)
872
873
874What's wrong?
875
876Your interpreter doesn't know how to communicate with these extensions
877on its own. A little glue will help. Up until now you've been
878calling I<perl_parse()>, handing it NULL for the second argument:
879
880 perl_parse(my_perl, NULL, argc, my_argv, NULL);
881
882That's where the glue code can be inserted to create the initial contact between
883Perl and linked C/C++ routines. Let's take a look some pieces of I<perlmain.c>
884to see how Perl does this:
885
886
887 #ifdef __cplusplus
888 # define EXTERN_C extern "C"
889 #else
890 # define EXTERN_C extern
891 #endif
892
893 static void xs_init _((void));
894
895 EXTERN_C void boot_DynaLoader _((CV* cv));
896 EXTERN_C void boot_Socket _((CV* cv));
897
898
899 EXTERN_C void
900 xs_init()
901 {
902 char *file = __FILE__;
903 /* DynaLoader is a special case */
904 newXS("DynaLoader::boot_DynaLoader", boot_DynaLoader, file);
905 newXS("Socket::bootstrap", boot_Socket, file);
906 }
907
908Simply put: for each extension linked with your Perl executable
909(determined during its initial configuration on your
910computer or when adding a new extension),
911a Perl subroutine is created to incorporate the extension's
912routines. Normally, that subroutine is named
913I<Module::bootstrap()> and is invoked when you say I<use Module>. In
914turn, this hooks into an XSUB, I<boot_Module>, which creates a Perl
915counterpart for each of the extension's XSUBs. Don't worry about this
916part; leave that to the I<xsubpp> and extension authors. If your
917extension is dynamically loaded, DynaLoader creates I<Module::bootstrap()>
918for you on the fly. In fact, if you have a working DynaLoader then there
5f05dabc 919is rarely any need to link in any other extensions statically.
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920
921
922Once you have this code, slap it into the second argument of I<perl_parse()>:
923
924
925 perl_parse(my_perl, xs_init, argc, my_argv, NULL);
926
927
928Then compile:
929
8a7dc658 930 % cc -o interp interp.c `perl -MExtUtils::Embed -e ccopts -e ldopts`
96dbc785
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931
932 % interp
933 use Socket;
934 use SomeDynamicallyLoadedModule;
935
936 print "Now I can use extensions!\n"'
937
938B<ExtUtils::Embed> can also automate writing the I<xs_init> glue code.
939
8a7dc658 940 % perl -MExtUtils::Embed -e xsinit -- -o perlxsi.c
96dbc785
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941 % cc -c perlxsi.c `perl -MExtUtils::Embed -e ccopts`
942 % cc -c interp.c `perl -MExtUtils::Embed -e ccopts`
8a7dc658 943 % cc -o interp perlxsi.o interp.o `perl -MExtUtils::Embed -e ldopts`
96dbc785
PP
944
945Consult L<perlxs> and L<perlguts> for more details.
946
947
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948=head1 MORAL
949
950You can sometimes I<write faster code> in C, but
5f05dabc 951you can always I<write code faster> in Perl. Because you can use
cb1a09d0
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952each from the other, combine them as you wish.
953
954
955=head1 AUTHOR
956
9607fc9c
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957Jon Orwant and <F<orwant@tpj.com>> and Doug MacEachern <F<dougm@osf.org>>,
958with small contributions from Tim Bunce, Tom Christiansen, Hallvard Furuseth,
959Dov Grobgeld, and Ilya Zakharevich.
8a7dc658
JO
960
961Check out Doug's article on embedding in Volume 1, Issue 4 of The Perl
962Journal. Info about TPJ is available from http://tpj.com.
cb1a09d0 963
137443ea 964April 14, 1997
cb1a09d0 965
8a7dc658
JO
966Some of this material is excerpted from Jon Orwant's book: I<Perl 5
967Interactive>, Waite Group Press, 1996 (ISBN 1-57169-064-6) and appears
cb1a09d0 968courtesy of Waite Group Press.
8a7dc658
JO
969
970=head1 COPYRIGHT
971
972Copyright (C) 1995, 1996, 1997 Doug MacEachern and Jon Orwant. All
973Rights Reserved.
974
975Although destined for release with the standard Perl distribution,
976this document is not public domain, nor is any of Perl and its
977documentation. Permission is granted to freely distribute verbatim
978copies of this document provided that no modifications outside of
979formatting be made, and that this notice remain intact. You are
980permitted and encouraged to use its code and derivatives thereof in
981your own source code for fun or for profit as you see fit.