BSD 4_4 development

[unix-history] / usr / src / contrib / rc-1.4 / execve.c

/* execve.c: an execve() for geriatric unices without #! */

/*
  NOTE: this file depends on a hack in footobar.c which places two free spots before
  av[][] so that execve does not have to call malloc.
*/

#include <errno.h>
#include "rc.h"

#define giveupif(x) { if (x) goto fail; }

extern int my_execve(const char *path, const char **av, const char **ev) {
       int fd, len, fst, snd, end;
       bool noarg;
       char pb[256]; /* arbitrary but generous limit */
       execve(path, av, ev);
       if (errno != ENOEXEC)
               return -1;
       fd = rc_open(path, rFrom);
       giveupif(fd < 0);
       len = read(fd, pb, sizeof pb);
       close(fd);
       /* reject scripts which don't begin with #! */
       giveupif(len <= 0 || pb[0] != '#' || pb[1] != '!');
       for (fst = 2; fst < len && (pb[fst] == ' ' || pb[fst] == '\t'); fst++)
               ; /* skip leading whitespace */
       giveupif(fst == len);
       for (snd = fst; snd < len && pb[snd] != ' ' && pb[snd] != '\t' && pb[snd] != '\n'; snd++)
               ; /* skip first arg */
       giveupif(snd == len);
       noarg = (pb[snd] == '\n');
       pb[snd++] = '\0'; /* null terminate the first arg */
       if (!noarg) {
               while (snd < len && (pb[snd] == ' ' || pb[snd] == '\t'))
                       snd++; /* skip whitespace to second arg */
               giveupif(snd == len);
               noarg = (pb[snd] == '\n'); /* could have trailing whitespace after only one arg */
               if (!noarg) {
                       for (end = snd; end < len && pb[end] != ' ' && pb[end] != '\t' && pb[end] != '\n'; end++)
                               ; /* skip to the end of the second arg */
                       giveupif(end == len);
                       if (pb[end] == '\n') {
                               pb[end] = '\0'; /* null terminate the first arg */
                       } else {                /* else check for a spurious third arg */
                               pb[end++] = '\0';
                               while (end < len && (pb[end] == ' ' || pb[end] == '\t'))
                                       end++;
                               giveupif(end == len || pb[end] != '\n');
                       }
               }
       }
       *av = path;
       if (!noarg)
               *--av = pb + snd;
       *--av = pb + fst;
       execve(*av, av, ev);
       return -1;
fail:   errno = ENOEXEC;
       return -1;
}