This is pty/script.c (Listing 64-3, page 1392), 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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In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.


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Function list (Bold in this list means a function is not static)

/* script.c

   A simple version of script(1).
#include <sys/stat.h>
#include <fcntl.h>
#include <libgen.h>
#include <termios.h>
#if ! defined(__hpux)
/* HP-UX 11 doesn't have this header file */
#include <sys/select.h>
#include "pty_fork.h"           /* Declaration of ptyFork() */
#include "tty_functions.h"      /* Declaration of ttySetRaw() */
#include "tlpi_hdr.h"

#define BUF_SIZE 256
#define MAX_SNAME 1000

struct termios ttyOrig;
static void             /* Reset terminal mode on program exit */
    if (tcsetattr(STDIN_FILENO, TCSANOW, &ttyOrig) == -1)
main(int argc, char *argv[])
    char slaveName[MAX_SNAME];
    char *shell;
    int masterFd, scriptFd;
    struct winsize ws;
    fd_set inFds;
    char buf[BUF_SIZE];
    ssize_t numRead;
    pid_t childPid;

    /* Retrieve the attributes of terminal on which we are started */

    if (tcgetattr(STDIN_FILENO, &ttyOrig) == -1)
    if (ioctl(STDIN_FILENO, TIOCGWINSZ, &ws) < 0)

    /* Create a child process, with parent and child connected via a
       pty pair. The child is connected to the pty slave and its terminal
       attributes are set to be the same as those retrieved above. */

    childPid = ptyFork(&masterFd, slaveName, MAX_SNAME, &ttyOrig, &ws);
    if (childPid == -1)

    if (childPid == 0) {        /* Child: execute a shell on pty slave */

        /* If the SHELL variable is set, use its value to determine
           the shell execed in child. Otherwise use /bin/sh. */

        shell = getenv("SHELL");
        if (shell == NULL || *shell == '\0')
            shell = "/bin/sh";

        execlp(shell, shell, (char *) NULL);
        errExit("execlp");      /* If we get here, something went wrong */

    /* Parent: relay data between terminal and pty master */

    scriptFd = open((argc > 1) ? argv[1] : "typescript",
                        O_WRONLY | O_CREAT | O_TRUNC,
                        S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP |
                                S_IROTH | S_IWOTH);
    if (scriptFd == -1)
        errExit("open typescript");

    /* Place terminal in raw mode so that we can pass all terminal
     input to the pseudoterminal master untouched */

    ttySetRaw(STDIN_FILENO, &ttyOrig);

    if (atexit(ttyReset) != 0)

    /* Loop monitoring terminal and pty master for input. If the
       terminal is ready for input, then read some bytes and write
       them to the pty master. If the pty master is ready for input,
       then read some bytes and write them to the terminal. */

    for (;;) {
        FD_SET(STDIN_FILENO, &inFds);
        FD_SET(masterFd, &inFds);

        if (select(masterFd + 1, &inFds, NULL, NULL, NULL) == -1)

        if (FD_ISSET(STDIN_FILENO, &inFds)) {   /* stdin --> pty */
            numRead = read(STDIN_FILENO, buf, BUF_SIZE);
            if (numRead <= 0)

            if (write(masterFd, buf, numRead) != numRead)
                fatal("partial/failed write (masterFd)");

        if (FD_ISSET(masterFd, &inFds)) {      /* pty --> stdout+file */
            numRead = read(masterFd, buf, BUF_SIZE);
            if (numRead <= 0)

            if (write(STDOUT_FILENO, buf, numRead) != numRead)
                fatal("partial/failed write (STDOUT_FILENO)");
            if (write(scriptFd, buf, numRead) != numRead)
                fatal("partial/failed write (scriptFd)");


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