#!/usr/bin/perl

system "/bin/echo", "hello";
# or
# system "/bin/echo hello";
# or 
# my $out = `/bin/echo hello`;

##</code><code>##

/* fakesys.c */
#include <unistd.h>   /* for execvp */
#include <dlfcn.h>    /* for dlsym */
#include <stdio.h>

static int (*real_execvp)(const char *file, char *const argv[]);

int execvp(const char *file, char *const argv[]) {
    char *msg;
    
    /* lookup original shared lib function */
    real_execvp = dlsym(RTLD_NEXT, "execvp");   /* see dlsym(3) */
    if ( (msg = dlerror() ) != NULL ) {
        fprintf(stderr, "dlopen of execvp() failed : %s\n", msg);
    }
    
    fprintf(stderr, "calling execvp(\"%s\", ...)\n", file);
    
    /* execute original lib function */
    return real_execvp(file, argv);
}

##</code><code>##

$ gcc -D_GNU_SOURCE -fPIC -shared fakesys.c -o libfakesys.so

##</code><code>##

$ LD_PRELOAD=./libfakesys.so perl ./685699.pl

##</code><code>##

calling execvp("/bin/echo", ...)
hello