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execve()               COHERENT System Call              execve()




Execute a load module

eexxeeccvvee(_f_i_l_e, _a_r_g_v, _e_n_v)
cchhaarr *_f_i_l_e, *_a_r_g_v[], *_e_n_v[];

The COHERENT  system includes six functions  that allow a process
to execute another  executable file (or load module, as described
in the header  l.out.h).  execve specifies arguments as a single,
NULL-terminated array  of parameters, called  argv.  The argument
env is the address of an array of pointers to strings that define
file's environment.  This allows execve to pass a new environment
to the  program being executed.  For  more information on program
execution, see execl.

***** Example *****

The  following example  demonstrates execve,  as well  as tmpnam,
getenv,  and  path.  It  finds  all lines  with  more than  LIMIT
characters and call MicroEMACS to edit them.


#include <stdio.h>
#include <path.h>
#include <sys/stat.h>



#define LIMIT 70



extern char *getenv(), **environ, *tempnam();



main(argc, argv)
char *argv[];
{
        /*                me     -e   tmp   file */
        char *cmda[5] = { NULL, "-e", NULL, NULL, NULL };
        FILE *ifp, *tmp;
        char line[256];
        int  ct, len;



        if ((NULL == (cmda[3] = argv[1])) ||
            (NULL == (ifp = fopen(argv[1], "r")))) {
                fprintf(stderr, "Cannot open %s\n", argv[1]);
                exit(1);
        }





COHERENT Lexicon                                           Page 1




execve()               COHERENT System Call              execve()




        if (cmda[0] = path(getenv("PATH"), "me", AEXEC) == NULL) {
                fprintf(stderr, "Cannot locate me\n");
                exit(1);
        }



        if (NULL == (tmp = fopen((cmda[2] = tempnam(NULL, "lng")), "w"))) {
                fprintf(stderr, "Cannot open tmpfile\n");
                exit(1);
        }



        for (ct = 1; NULL != fgets(line, sizeof(line), ifp); ct++)
                if (((len = strlen(line)) > LIMIT) ||
                    ('\n' != line[len -1]))
                        fprintf(tmp, "%d: %d characters long\n", ct, len);



        fclose(tmp);
        fclose(ifp);



        if (execve(cmda[0], cmda, environ) < 0) {
                fprintf(stderr, "cannot execute me\n");
                exit(1);
        }
        /* We never reach here ! */
}


***** See Also *****

COHERENT system calls, environ, execution

***** Diagnostics *****

execve does not return  if successful.  It returns -1 for errors,
such as file  being nonexistent, not accessible with execute per-
mission, having a bad format, or too large to fit in memory.













COHERENT Lexicon                                           Page 2

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