IRIX Base Documentation 2002 November/SGI IRIX Base Documentation 2002 November.iso/usr/share/catman/u_man/cat1/perlembed.z/perlembed

Text File | 2002-10-03 | 49.4 KB | 1,387 lines

PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



NNNNAAAAMMMMEEEE
     perlembed - how to embed perl in your C program

DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
     PPPPRRRREEEEAAAAMMMMBBBBLLLLEEEE

     Do you want to:

     UUUUsssseeee CCCC ffffrrrroooommmm PPPPeeeerrrrllll????
          Read the _p_e_r_l_x_s_t_u_t manpage, the _p_e_r_l_x_s manpage, the _h_2_x_s manpage,
          and the _p_e_r_l_g_u_t_s manpage.

     UUUUsssseeee aaaa UUUUnnnniiiixxxx pppprrrrooooggggrrrraaaammmm ffffrrrroooommmm PPPPeeeerrrrllll????
          Read about back-quotes and about system and exec in the _p_e_r_l_f_u_n_c
          manpage.

     UUUUsssseeee PPPPeeeerrrrllll ffffrrrroooommmm PPPPeeeerrrrllll????
          Read about the do entry in the _p_e_r_l_f_u_n_c manpage and the eval entry
          in the _p_e_r_l_f_u_n_c manpage and the require entry in the _p_e_r_l_f_u_n_c
          manpage and the use entry in the _p_e_r_l_f_u_n_c manpage.

     UUUUsssseeee CCCC ffffrrrroooommmm CCCC????
          Rethink your design.

     UUUUsssseeee PPPPeeeerrrrllll ffffrrrroooommmm CCCC????
          Read on...

     RRRROOOOAAAADDDDMMMMAAAAPPPP

     the section on _C_o_m_p_i_l_i_n_g _y_o_u_r _C _p_r_o_g_r_a_m

     the section on _A_d_d_i_n_g _a _P_e_r_l _i_n_t_e_r_p_r_e_t_e_r _t_o _y_o_u_r _C _p_r_o_g_r_a_m

     the section on _C_a_l_l_i_n_g _a _P_e_r_l _s_u_b_r_o_u_t_i_n_e _f_r_o_m _y_o_u_r _C _p_r_o_g_r_a_m

     the section on _E_v_a_l_u_a_t_i_n_g _a _P_e_r_l _s_t_a_t_e_m_e_n_t _f_r_o_m _y_o_u_r _C _p_r_o_g_r_a_m

     the section on _P_e_r_f_o_r_m_i_n_g _P_e_r_l _p_a_t_t_e_r_n _m_a_t_c_h_e_s _a_n_d _s_u_b_s_t_i_t_u_t_i_o_n_s _f_r_o_m
     _y_o_u_r _C _p_r_o_g_r_a_m

     the section on _F_i_d_d_l_i_n_g _w_i_t_h _t_h_e _P_e_r_l _s_t_a_c_k _f_r_o_m _y_o_u_r _C _p_r_o_g_r_a_m

     the section on _M_a_i_n_t_a_i_n_i_n_g _a _p_e_r_s_i_s_t_e_n_t _i_n_t_e_r_p_r_e_t_e_r

     the section on _M_a_i_n_t_a_i_n_i_n_g _m_u_l_t_i_p_l_e _i_n_t_e_r_p_r_e_t_e_r _i_n_s_t_a_n_c_e_s

     the section on _U_s_i_n_g _P_e_r_l _m_o_d_u_l_e_s, _w_h_i_c_h _t_h_e_m_s_e_l_v_e_s _u_s_e _C _l_i_b_r_a_r_i_e_s, _f_r_o_m
     _y_o_u_r _C _p_r_o_g_r_a_m

     the section on _E_m_b_e_d_d_i_n_g _P_e_r_l _u_n_d_e_r _W_i_n_3_2





                                                                        PPPPaaaaggggeeee 1111






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



     CCCCoooommmmppppiiiilllliiiinnnngggg yyyyoooouuuurrrr CCCC pppprrrrooooggggrrrraaaammmm

     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 _p_e_r_l _l_i_b_r_a_r_y.
     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 (/_u_s_r/_b_i_n/_p_e_r_l 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 _l_i_b
     directory.)

     When you use Perl from C, your C program will--usually--allocate, "run",
     and deallocate a _P_e_r_l_I_n_t_e_r_p_r_e_t_e_r 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 _E_X_T_E_R_N._h and _p_e_r_l._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, the section on
     _A_d_d_i_n_g _a _P_e_r_l _i_n_t_e_r_p_r_e_t_e_r _t_o _y_o_u_r _C _p_r_o_g_r_a_m, 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



                                                                        PPPPaaaaggggeeee 2222






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



     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 (_c_c, _g_c_c, 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
     (/_u_s_r/_l_o_c_a_l/_l_i_b/...) for your machine.  If your compiler complains that
     certain functions are undefined, or that it can't locate -_l_p_e_r_l, then you
     need to change the path following the -L.  If it complains that it can't
     find _E_X_T_E_R_N._h and _p_e_r_l._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
     EEEExxxxttttUUUUttttiiiillllssss::::::::EEEEmmmmbbbbeeeedddd module will determine all of this information for you:

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

     If the EEEExxxxttttUUUUttttiiiillllssss::::::::EEEEmmmmbbbbeeeedddd 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 EEEExxxxttttUUUUttttiiiillllssss::::::::EEEEmmmmbbbbeeeedddd kit on CPAN also contains all source code for the
     examples in this document, tests, additional examples and other
     information you may find useful.

     AAAAddddddddiiiinnnngggg aaaa PPPPeeeerrrrllll iiiinnnntttteeeerrrrpppprrrreeeetttteeeerrrr ttttoooo yyyyoooouuuurrrr CCCC pppprrrrooooggggrrrraaaammmm

     In a sense, perl (the C program) is a good example of embedding Perl (the
     language), so I'll demonstrate embedding with _m_i_n_i_p_e_r_l_m_a_i_n._c, included in
     the source distribution.  Here's a bastardized, nonportable version of
     _m_i_n_i_p_e_r_l_m_a_i_n._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    ***/











                                                                        PPPPaaaaggggeeee 3333






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



         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 _i_n_t_e_r_p._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_n_t_e_r_p 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 _a_r_g_v[_1] before
     calling _p_e_r_l__r_u_n.

     CCCCaaaalllllllliiiinnnngggg aaaa PPPPeeeerrrrllll ssssuuuubbbbrrrroooouuuuttttiiiinnnneeee ffffrrrroooommmm yyyyoooouuuurrrr CCCC pppprrrrooooggggrrrraaaammmm

     To call individual Perl subroutines, you can use any of the ppppeeeerrrrllll____ccccaaaallllllll____****
     functions documented in the _p_e_r_l_c_a_l_l manpage.  In this example we'll use
     perl_call_argv.

     That's shown below, in a program I'll call _s_h_o_w_t_i_m_e._c.

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

         static PerlInterpreter *my_perl;






                                                                        PPPPaaaaggggeeee 4444






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



         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 _s_h_o_w_t_i_m_e is a Perl subroutine that takes no arguments (that's the
     _G__N_O_A_R_G_S) and for which I'll ignore the return value (that's the
     _G__D_I_S_C_A_R_D).  Those flags, and others, are discussed in the _p_e_r_l_c_a_l_l
     manpage.

     I'll define the _s_h_o_w_t_i_m_e subroutine in a file called _s_h_o_w_t_i_m_e._p_l:

         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 _p_e_r_l__r_u_n, 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 _p_e_r_l__c_a_l_l__a_r_g_v.  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:
     the section on _F_i_d_d_l_i_n_g _w_i_t_h _t_h_e _P_e_r_l _s_t_a_c_k _f_r_o_m _y_o_u_r _C _p_r_o_g_r_a_m.





                                                                        PPPPaaaaggggeeee 5555






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



     EEEEvvvvaaaalllluuuuaaaattttiiiinnnngggg aaaa PPPPeeeerrrrllll ssssttttaaaatttteeeemmmmeeeennnntttt ffffrrrroooommmm yyyyoooouuuurrrr CCCC pppprrrrooooggggrrrraaaammmm

     Perl provides two API functions to evaluate pieces of Perl code.  These
     are the perl_eval_sv entry in the _p_e_r_l_g_u_t_s manpage and the perl_eval_pv
     entry in the _p_e_r_l_g_u_t_s manpage.

     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 the
     use entry in the _p_e_r_l_f_u_n_c manpage, the require entry in the _p_e_r_l_f_u_n_c
     manpage, and the do entry in the _p_e_r_l_f_u_n_c manpage to include external
     Perl files.

     _p_e_r_l__e_v_a_l__p_v lets us evaluate individual Perl strings, and then extract
     variables for coercion into C types.  The following program, _s_t_r_i_n_g._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;

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

            my_perl = perl_alloc();
            perl_construct( my_perl );

            perl_parse(my_perl, NULL, 3, embedding, NULL);
            perl_run(my_perl);

            /** Treat $a as an integer **/
            perl_eval_pv("$a = 3; $a **= 2", TRUE);
            printf("a = %d\n", SvIV(perl_get_sv("a", FALSE)));

            /** Treat $a as a float **/
            perl_eval_pv("$a = 3.14; $a **= 2", TRUE);
            printf("a = %f\n", SvNV(perl_get_sv("a", FALSE)));

            /** Treat $a as a string **/
            perl_eval_pv("$a = 'rekcaH lreP rehtonA tsuJ'; $a = reverse($a);", TRUE);
            printf("a = %s\n", SvPV(perl_get_sv("a", FALSE), PL_na));

            perl_destruct(my_perl);
            perl_free(my_perl);
        }

     All of those strange functions with _s_v in their names help convert Perl
     scalars to C types.  They're described in the _p_e_r_l_g_u_t_s manpage.




                                                                        PPPPaaaaggggeeee 6666






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



     If you compile and run _s_t_r_i_n_g._c, you'll see the results of using _S_v_I_V()
     to create an int, _S_v_N_V() to create a float, and _S_v_P_V() 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'd expression.  It is also possible
     and in most cases a better strategy to fetch the return value from
     _p_e_r_l__e_v_a_l__p_v() instead.  Example:

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

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

     PPPPeeeerrrrffffoooorrrrmmmmiiiinnnngggg PPPPeeeerrrrllll ppppaaaatttttttteeeerrrrnnnn mmmmaaaattttcccchhhheeeessss aaaannnndddd ssssuuuubbbbssssttttiiiittttuuuuttttiiiioooonnnnssss ffffrrrroooommmm yyyyoooouuuurrrr CCCC pppprrrrooooggggrrrraaaammmm

     The _p_e_r_l__e_v_a_l__s_v() function lets us evaluate strings of Perl code, so we
     can define some functions that use it to "specialize" in matches and
     substitutions: _m_a_t_c_h(), _s_u_b_s_t_i_t_u_t_e(), and _m_a_t_c_h_e_s().

        I32 match(SV *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/"), _m_a_t_c_h() returns 1 if the
     string matches the pattern and 0 otherwise.

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

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

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

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

     Here's a sample program, _m_a_t_c_h._c, that uses all three (long lines have
     been wrapped here):








                                                                        PPPPaaaaggggeeee 7777






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



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

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

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

          SPAGAIN;
          retval = POPs;
          PUTBACK;

          if (croak_on_error && SvTRUE(ERRSV))
             croak(SvPVx(ERRSV, PL_na));

          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(1099, 0), *retval;

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

          retval = my_perl_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.
      **/



                                                                        PPPPaaaaggggeeee 8888






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))




      I32 substitute(SV **string, char *pattern)
      {
          SV *command = NEWSV(1099, 0), *retval;

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

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

          *string = perl_get_sv("string", FALSE);
          return SvIV(retval);
      }

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

      I32 matches(SV *string, char *pattern, AV **match_list)
      {
          SV *command = NEWSV(1099, 0);
          I32 num_matches;

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

          my_perl_eval_sv(command, TRUE);
          SvREFCNT_dec(command);

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

          return num_matches;
      }

      main (int argc, char **argv, char **env)
      {
          PerlInterpreter *my_perl = perl_alloc();
          char *embedding[] = { "", "-e", "0" };
          AV *match_list;
          I32 num_matches, i;
          SV *text = NEWSV(1099,0);

          perl_construct(my_perl);
          perl_parse(my_perl, NULL, 3, embedding, NULL);

          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");



                                                                        PPPPaaaaggggeeee 9999






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))




          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(*av_fetch(match_list, i, FALSE),PL_na));
          printf("\n");

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

          /** 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);
      }

     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








                                                                       PPPPaaaaggggeeee 11110000






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



        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.


     FFFFiiiiddddddddlllliiiinnnngggg wwwwiiiitttthhhh tttthhhheeee PPPPeeeerrrrllll ssssttttaaaacccckkkk ffffrrrroooommmm yyyyoooouuuurrrr CCCC pppprrrrooooggggrrrraaaammmm

     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 _n_e_w_S_V_i_v() and _s_v__s_e_t_n_v() and _n_e_w_A_V() and all their friends.  They're
     described in the _p_e_r_l_g_u_t_s manpage.

     Then you'll need to know how to manipulate the Perl stack.  That's
     described in the _p_e_r_l_c_a_l_l manpage.

     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 _p_o_w() function).  First I'll create a
     stub exponentiation function in _p_o_w_e_r._p_l:

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

     Now I'll create a C program, _p_o_w_e_r._c, with a function _P_e_r_l_P_o_w_e_r() that
     contains all the perlguts necessary to push the two arguments into _e_x_p_o()
     and to pop the return value out.  Take a deep breath...

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

         static PerlInterpreter *my_perl;









                                                                       PPPPaaaaggggeeee 11111111






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



         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[] = { "", "power.pl" };

           my_perl = perl_alloc();
           perl_construct( my_perl );

           perl_parse(my_perl, NULL, 2, my_argv, (char **)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.


     MMMMaaaaiiiinnnnttttaaaaiiiinnnniiiinnnngggg aaaa ppppeeeerrrrssssiiiisssstttteeeennnntttt iiiinnnntttteeeerrrrpppprrrreeeetttteeeerrrr

     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.






                                                                       PPPPaaaaggggeeee 11112222






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



     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 the eval entry in the _p_e_r_l_f_u_n_c manpage.  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 the perl_call_argv entry in
     the _p_e_r_l_c_a_l_l manpage, 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 the my entry in the
     _p_e_r_l_f_u_n_c manpage whenever possible.

      package Embed::Persistent;
      #persistent.pl

      use strict;
      use vars '%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;
      }






                                                                       PPPPaaaaggggeeee 11113333






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



      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>







                                                                       PPPPaaaaggggeeee 11114444






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



      /* 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(ERRSV))
                     fprintf(stderr, "eval error: %s\n", SvPV(ERRSV,PL_na));
             }
          }

          PL_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:





                                                                       PPPPaaaaggggeeee 11115555






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



      #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


     MMMMaaaaiiiinnnnttttaaaaiiiinnnniiiinnnngggg mmmmuuuullllttttiiiipppplllleeee iiiinnnntttteeeerrrrpppprrrreeeetttteeeerrrr iiiinnnnssssttttaaaannnncccceeeessss

     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 _b_e_f_o_r_e the
     next interpreter is constructed.  By default, the global variable
     PL_perl_destruct_level is set to 0, since extra cleaning isn't needed
     when a program has only one interpreter.

     Setting PL_perl_destruct_level to 1 makes everything squeaky clean:

      PL_perl_destruct_level = 1;

      while(1) {
          ...
          /* reset global variables here with PL_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 _p_e_r_l__d_e_s_t_r_u_c_t() 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 PL_perl_destruct_level to



                                                                       PPPPaaaaggggeeee 11116666






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



     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


     UUUUssssiiiinnnngggg PPPPeeeerrrrllll mmmmoooodddduuuulllleeeessss,,,, wwwwhhhhiiiicccchhhh tttthhhheeeemmmmsssseeeellllvvvveeeessss uuuusssseeee CCCC lllliiiibbbbrrrraaaarrrriiiieeeessss,,,, ffffrrrroooommmm yyyyoooouuuurrrr CCCC pppprrrrooooggggrrrraaaammmm

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



                                                                       PPPPaaaaggggeeee 11117777






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



      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
     _p_e_r_l__p_a_r_s_e(), 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
     _p_e_r_l_m_a_i_n._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
     _M_o_d_u_l_e::_b_o_o_t_s_t_r_a_p() and is invoked when you say _u_s_e _M_o_d_u_l_e.  In turn,
     this hooks into an XSUB, _b_o_o_t__M_o_d_u_l_e, which creates a Perl counterpart
     for each of the extension's XSUBs.  Don't worry about this part; leave
     that to the _x_s_u_b_p_p and extension authors.  If your extension is
     dynamically loaded, DynaLoader creates _M_o_d_u_l_e::_b_o_o_t_s_t_r_a_p() 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
     _p_e_r_l__p_a_r_s_e():





                                                                       PPPPaaaaggggeeee 11118888






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



      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"'

     EEEExxxxttttUUUUttttiiiillllssss::::::::EEEEmmmmbbbbeeeedddd can also automate writing the _x_s__i_n_i_t 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 _p_e_r_l_x_s manpage and the _p_e_r_l_g_u_t_s manpage for more details.

EEEEmmmmbbbbeeeeddddddddiiiinnnngggg PPPPeeeerrrrllll uuuunnnnddddeeeerrrr WWWWiiiinnnn33332222
     At the time of this writing (5.004), there are two versions of Perl which
     run under Win32.  (The two versions are merging in 5.005.)  Interfacing
     to ActiveState's Perl library is quite different from the examples in
     this documentation, as significant changes were made to the internal Perl
     API.  However, it is possible to embed ActiveState's Perl runtime.  For
     details, see the Perl for Win32 FAQ at
     http://www.perl.com/perl/faq/win32/Perl_for_Win32_FAQ.html.

     With the "official" Perl version 5.004 or higher, all the examples within
     this documentation will compile and run untouched, although the build
     process is slightly different between Unix and Win32.

     For starters, backticks don't work under the Win32 native command shell.
     The ExtUtils::Embed kit on CPAN ships with a script called ggggeeeennnnmmmmaaaakkkkeeee, which
     generates a simple makefile to build a program from a single C source
     file.  It can be used like this:

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

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

      perl -MExtUtils::Embed -e xsinit

     Create a new project and Insert -> Files into Project: perlxsi.c,
     perl.lib, and your own source files, e.g. interp.c.  Typically you'll
     find perl.lib in CCCC::::\\\\ppppeeeerrrrllll\\\\lllliiiibbbb\\\\CCCCOOOORRRREEEE, if not, you should see the CCCCOOOORRRREEEE
     directory relative to perl -V:archlib.  The studio will also need this



                                                                       PPPPaaaaggggeeee 11119999






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))



     path so it knows where to find Perl include files.  This path can be
     added via the Tools -> Options -> Directories menu.  Finally, select
     Build -> Build interp.exe and you're ready to go.

MMMMOOOORRRRAAAALLLL
     You can sometimes _w_r_i_t_e _f_a_s_t_e_r _c_o_d_e in C, but you can always _w_r_i_t_e _c_o_d_e
     _f_a_s_t_e_r in Perl.  Because you can use each from the other, combine them as
     you wish.

AAAAUUUUTTTTHHHHOOOORRRR
     Jon Orwant <_o_r_w_a_n_t@_t_p_j._c_o_m> and Doug MacEachern <_d_o_u_g_m@_o_s_f._o_r_g>, with
     small contributions from Tim Bunce, Tom Christiansen, Guy Decoux,
     Hallvard Furuseth, Dov Grobgeld, and Ilya Zakharevich.

     Doug MacEachern has an article on embedding in Volume 1, Issue 4 of The
     Perl Journal (http://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.

     July 22, 1998

CCCCOOOOPPPPYYYYRRRRIIIIGGGGHHHHTTTT
     Copyright (C) 1995, 1996, 1997, 1998 Doug MacEachern and Jon Orwant.  All
     Rights Reserved.

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

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

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














                                                                       PPPPaaaaggggeeee 22220000






PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))                                                      PPPPEEEERRRRLLLLEEEEMMMMBBBBEEEEDDDD((((1111))))























































                                                                       PPPPaaaaggggeeee 22221111