Advanced Perl Programming

Examples

Let us now write some code to see this API in action. Suppose you have a Perl script, search.pl, containing subroutine search_files , defined in Example 19.1.

Example 19-1. search.pl

# search_files - a simple grep. Called as ...
#    search_files ("struct", "*.h")
sub search_files {
    my ($pattern, $filepattern) = @_;
    local (@ARGV) = glob($filepattern);
    return unless (@ARGV);
    while (<>) {       # Can do this because @ARGV has been primed
        if (/$pattern/o) {
            print "$ARGV\[$.\]: $_"; # File, line number, match line
        }
    }
}

search_files takes two string parameters and returns nothing. There are several ways of calling this procedure from C. Let’s start with perl_call_argv() , since it takes string arguments. The piece of code in Example 19.2 searches for the word “struct” in all C header files.

Example 19-2. ex.c: Embedding Perl

#include <EXTERN.h>
#include <perl.h>
static PerlInterpreter *my_perl;  
main(int argc, char **argv, char **env) {

    char *my_argv[] = {"struct", "*.h", NULL};
    my_perl = perl_alloc();
    perl_construct(my_perl);
    perl_parse(my_perl, NULL, argc, argv, env);


    perl_call_argv("search_files", G_DISCARD, my_argv);

    perl_destruct(my_perl);
    perl_free(my_perl);
}

By passing NULL instead of xs_init, we indicate to perl_parse that we are not interested in loading any extensions. In addition, instead of calling perl_run, we call search_files using perl_call_argv (with the G_DISCARD flag to tell it to discard all returned results). This is how I compile and link this code on a Linux box: ...