This is signals/sig_sender.c (Listing 20-6, page 412), 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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/* sig_sender.c

   Usage: sig_sender PID num-sigs sig [sig2]

   Send signals to sig_receiver.c.

   Sends 'num-sigs' signals of type 'sig' to the process with the specified PID.
   If a fourth command-line argument is supplied, send one instance of that
   signal, after sending the previous signals.
#include <signal.h>
#include "tlpi_hdr.h"
main(int argc, char *argv[])
    int numSigs, sig, j;
    pid_t pid;

    if (argc < 4 || strcmp(argv[1], "--help") == 0)
        usageErr("%s pid num-sigs sig-num [sig-num-2]\n", argv[0]);

    pid = getLong(argv[1], 0, "PID");
    numSigs = getInt(argv[2], GN_GT_0, "num-sigs");
    sig = getInt(argv[3], 0, "sig-num");

    /* Send signals to receiver */

    printf("%s: sending signal %d to process %ld %d times\n",
            argv[0], sig, (long) pid, numSigs);

    for (j = 0; j < numSigs; j++)
        if (kill(pid, sig) == -1)

    /* If a fourth command-line argument was specified, send that signal */

    if (argc > 4)
        if (kill(pid, getInt(argv[4], 0, "sig-num-2")) == -1)

    printf("%s: exiting\n", argv[0]);


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