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| 1 | +/******************************************************************************* |
| 2 | + * access() checks whether the calling process can access the file pathname. If |
| 3 | + * pathname is a symbolic link, it is dereferenced. |
| 4 | + * |
| 5 | + * The mode specifies the accessibility check(s) to be performed, and is either |
| 6 | + * the value F_OK, or a mask consisting of the bitwise OR of one or more of R_OK, |
| 7 | + * W_OK, and X_OK. F_OK tests for the existence of the file. R_OK, W_OK, and |
| 8 | + * X_OK test whether the file exists and grants read, write, and execute permis‐ |
| 9 | + * sions, respectively. |
| 10 | + * |
| 11 | + * The check is done using the calling process's real UID and GID, rather than |
| 12 | + * the effective IDs as is done when actually attempting an operation (e.g., |
| 13 | + * open(2)) on the file. Similarly, for the root user, the check uses the set of |
| 14 | + * permitted capabilities rather than the set of effective capabilities; and for |
| 15 | + * non-root users, the check uses an empty set of capabilities. |
| 16 | + ******************************************************************************/ |
| 17 | + |
| 18 | +#include <stdlib.h> |
| 19 | +#include <stdio.h> |
| 20 | +#include <string.h> |
| 21 | +#include <unistd.h> |
| 22 | + |
| 23 | + |
| 24 | +void print_help(char *msg, int rc) |
| 25 | +{ |
| 26 | + if (msg != NULL) fprintf(stderr, "%s\n", msg); |
| 27 | + fprintf(stderr, "my_access -h\n"); |
| 28 | + fprintf(stderr, "my_access -f file\n"); |
| 29 | + fprintf(stderr, "my_access [-r] [-w] [-x] file\n"); |
| 30 | + fprintf(stderr, "\t-h\tPrint this help message\n"); |
| 31 | + fprintf(stderr, "\t-f\tTest for existence of file\n"); |
| 32 | + fprintf(stderr, "\t-r\tTest whether effective user can read file\n"); |
| 33 | + fprintf(stderr, "\t-w\tTest whether effective user can write file\n"); |
| 34 | + fprintf(stderr, "\t-x\tTest whether effective user can execute file\n"); |
| 35 | + exit(rc); |
| 36 | +} |
| 37 | + |
| 38 | +int my_access(const char *pathname, int mode) |
| 39 | +{ |
| 40 | +} |
| 41 | + |
| 42 | +int |
| 43 | +main(int argc, char *argv[]) |
| 44 | +{ |
| 45 | + int fname; /* Location of filename argument in argv[] */ |
| 46 | + int opt; |
| 47 | + int f_mode = 0; /* F_OK maps to zero (0) */ |
| 48 | + int rwx_mode = 0; |
| 49 | + char *invalid_opt_msg_fmt = "'%c' is an invalid option"; |
| 50 | + char *invalid_opt_msg; |
| 51 | + char *file_missing_msg = "file name is missing"; |
| 52 | + char *conflict_args_msg = "specify either -f or a combination of -r -w -x"; |
| 53 | + |
| 54 | + invalid_opt_msg = malloc(strlen(invalid_opt_msg_fmt)); |
| 55 | + while ((opt = getopt(argc, argv, ":hfrwx")) != -1) |
| 56 | + { |
| 57 | + switch (opt) |
| 58 | + { |
| 59 | + case 'f': f_mode = 1; break; |
| 60 | + case 'h': print_help(NULL, EXIT_SUCCESS); break; |
| 61 | + case 'r': rwx_mode |= R_OK; break; |
| 62 | + case 'w': rwx_mode |= W_OK; break; |
| 63 | + case 'x': rwx_mode |= X_OK; break; |
| 64 | + case '?': |
| 65 | + sprintf(invalid_opt_msg, invalid_opt_msg_fmt, (char)optopt); |
| 66 | + print_help(invalid_opt_msg, EXIT_FAILURE); |
| 67 | + break; |
| 68 | + } |
| 69 | + } |
| 70 | + |
| 71 | + fname = optind; |
| 72 | + |
| 73 | + if (fname >= argc) print_help(file_missing_msg, EXIT_FAILURE); |
| 74 | + if (f_mode == 0) |
| 75 | + { |
| 76 | + if (rwx_mode == 0) print_help(conflict_args_msg, EXIT_FAILURE); |
| 77 | + } |
| 78 | + else |
| 79 | + { |
| 80 | + if (rwx_mode != 0) print_help(conflict_args_msg, EXIT_FAILURE); |
| 81 | + } |
| 82 | + |
| 83 | + exit(EXIT_SUCCESS); |
| 84 | +} |
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