This is sockets/ud_ucase_cl.c (Listing 57-7, page 1173), 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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#include "ud_ucase.h"
main(int argc, char *argv[])
    struct sockaddr_un svaddr, claddr;
    int sfd, j;
    size_t msgLen;
    ssize_t numBytes;
    char resp[BUF_SIZE];

    if (argc < 2 || strcmp(argv[1], "--help") == 0)
        usageErr("%s msg...\n", argv[0]);

    /* Create client socket; bind to unique pathname (based on PID) */

    sfd = socket(AF_UNIX, SOCK_DGRAM, 0);
    if (sfd == -1)

    memset(&claddr, 0, sizeof(struct sockaddr_un));
    claddr.sun_family = AF_UNIX;
    snprintf(claddr.sun_path, sizeof(claddr.sun_path),
            "/tmp/ud_ucase_cl.%ld", (long) getpid());

    if (bind(sfd, (struct sockaddr *) &claddr, sizeof(struct sockaddr_un)) == -1)

    /* Construct address of server */

    memset(&svaddr, 0, sizeof(struct sockaddr_un));
    svaddr.sun_family = AF_UNIX;
    strncpy(svaddr.sun_path, SV_SOCK_PATH, sizeof(svaddr.sun_path) - 1);

    /* Send messages to server; echo responses on stdout */

    for (j = 1; j < argc; j++) {
        msgLen = strlen(argv[j]);       /* May be longer than BUF_SIZE */
        if (sendto(sfd, argv[j], msgLen, 0, (struct sockaddr *) &svaddr,
                sizeof(struct sockaddr_un)) != msgLen)

        numBytes = recvfrom(sfd, resp, BUF_SIZE, 0, NULL, NULL);
        if (numBytes == -1)
        printf("Response %d: %.*s\n", j, (int) numBytes, resp);

    remove(claddr.sun_path);            /* Remove client socket pathname */


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