71 lines
1.3 KiB
C
71 lines
1.3 KiB
C
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/stat.h>
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#include <sys/types.h>
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static void usage (void);
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mode_t
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calculate_permission (char *arg_str)
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{
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const char perms[4] = "rwx";
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if (strlen (arg_str) != 3)
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{
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usage ();
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exit (EXIT_FAILURE);
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}
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mode_t permission = 0;
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for (size_t j = 0; j < 3; j++)
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{
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int perm = 1 << (2 - j);
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if (arg_str[j] == perms[j])
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{
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permission |= perm;
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}
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else if (arg_str[j] != '-')
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{
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usage ();
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exit (EXIT_FAILURE);
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}
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}
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return permission;
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}
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int
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main (int argc, char **argv)
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{
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if (argc != 5)
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{
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usage ();
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return EXIT_FAILURE;
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}
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mode_t user = calculate_permission (argv[1]);
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mode_t group = calculate_permission (argv[2]);
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mode_t other = calculate_permission (argv[3]);
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mode_t permissions = (user << 6) | (group << 3) | other;
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if (chmod (argv[4], permissions) == -1)
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{
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perror ("Failed to chmod");
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return EXIT_FAILURE;
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}
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return EXIT_SUCCESS;
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}
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static void
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usage (void)
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{
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printf ("chmod, changes permissions on a file\n");
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printf ("usage: chmod USR GRP OTH FILE\n\n");
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printf ("USR, GRP, and OTH must be of the rwx format,\n");
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printf ("with - indicating a permission is not allwed.\n");
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}
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