This is files/t_chown.c (Listing 15-2, page 293), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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/* t_chown.c

   Demonstrate the use of the chown() system call to change the owner
   and group of a file.

   Usage: t_chown owner group [file...]

   Either or both of owner and/or group can be specified as "-" to
   leave them unchanged.
#include <pwd.h>
#include <grp.h>
#include "ugid_functions.h"             /* Declarations of userIdFromName()
                                           and groupIdFromName() */
#include "tlpi_hdr.h"
main(int argc, char *argv[])
    uid_t uid;
    gid_t gid;
    int j;
    Boolean errFnd;

    if (argc < 3 || strcmp(argv[1], "--help") == 0)
        usageErr("%s owner group [file...]\n"
                "        owner or group can be '-', "
                "meaning leave unchanged\n", argv[0]);

    if (strcmp(argv[1], "-") == 0) {            /* "-" ==> don't change owner */
        uid = -1;
    } else {                                    /* Turn user name into UID */
        uid = userIdFromName(argv[1]);
        if (uid == -1)
            fatal("No such user (%s)", argv[1]);

    if (strcmp(argv[2], "-") == 0) {            /* "-" ==> don't change group */
        gid = -1;
    } else {                                    /* Turn group name into GID */
        gid = groupIdFromName(argv[2]);
        if (gid == -1)
            fatal("No group user (%s)", argv[2]);

    /* Change ownership of all files named in remaining arguments */

    errFnd = FALSE;
    for (j = 3; j < argc; j++) {
        if (chown(argv[j], uid, gid) == -1) {
            errMsg("chown: %s", argv[j]);
            errFnd = TRUE;

    exit(errFnd ? EXIT_FAILURE : EXIT_SUCCESS);


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