tty/test_tty_functions.c

This is tty/test_tty_functions.c (Listing 62-4, page 1313), 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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/* test_tty_functions.c

   Put the terminal in raw mode (or cbreak if a command-line argument is
   supplied), allowing the program to read input a character at a time, and
   read and echo characters.

   Usage: test_tty_functions [x]

   See also tty_functions.c.
*/

#include <termios.h>
#include <signal.h>
#include <ctype.h>
#include "tty_functions.h"              /* Declarations of ttySetCbreak()
                                           and ttySetRaw() */
#include "tlpi_hdr.h"

static struct termios userTermios;
                        /* Terminal settings as defined by user */
static void             /* General handler: restore tty settings and exit */
handler(int sig)
{
    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &userTermios) == -1)
        errExit("tcsetattr");
    _exit(EXIT_SUCCESS);
}
static void             /* Handler for SIGTSTP */
tstpHandler(int sig)
{
    struct termios ourTermios;          /* To save our tty settings */
    sigset_t tstpMask, prevMask;
    struct sigaction sa;
    int savedErrno;

    savedErrno = errno;                 /* We might change 'errno' here */

    /* Save current terminal settings, restore terminal to
       state at time of program startup */

    if (tcgetattr(STDIN_FILENO, &ourTermios) == -1)
        errExit("tcgetattr");
    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &userTermios) == -1)
        errExit("tcsetattr");

    /* Set the disposition of SIGTSTP to the default, raise the signal
       once more, and then unblock it so that we actually stop */

    if (signal(SIGTSTP, SIG_DFL) == SIG_ERR)
        errExit("signal");
    raise(SIGTSTP);

    sigemptyset(&tstpMask);
    sigaddset(&tstpMask, SIGTSTP);
    if (sigprocmask(SIG_UNBLOCK, &tstpMask, &prevMask) == -1)
        errExit("sigprocmask");

    /* Execution resumes here after SIGCONT */

    if (sigprocmask(SIG_SETMASK, &prevMask, NULL) == -1)
        errExit("sigprocmask");         /* Reblock SIGTSTP */

    sigemptyset(&sa.sa_mask);           /* Reestablish handler */
    sa.sa_flags = SA_RESTART;
    sa.sa_handler = tstpHandler;
    if (sigaction(SIGTSTP, &sa, NULL) == -1)
        errExit("sigaction");

    /* The user may have changed the terminal settings while we were
       stopped; save the settings so we can restore them later */

    if (tcgetattr(STDIN_FILENO, &userTermios) == -1)
        errExit("tcgetattr");

    /* Restore our terminal settings */

    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &ourTermios) == -1)
        errExit("tcsetattr");

    errno = savedErrno;
}
int
main(int argc, char *argv[])
{
    char ch;
    struct sigaction sa, prev;
    ssize_t n;

    sigemptyset(&sa.sa_mask);
    sa.sa_flags = SA_RESTART;

    if (argc > 1) {                     /* Use cbreak mode */
        if (ttySetCbreak(STDIN_FILENO, &userTermios) == -1)
            errExit("ttySetCbreak");

        /* Terminal special characters can generate signals in cbreak
           mode. Catch them so that we can adjust the terminal mode.
           We establish handlers only if the signals are not being ignored. */

        sa.sa_handler = handler;

        if (sigaction(SIGQUIT, NULL, &prev) == -1)
            errExit("sigaction");
        if (prev.sa_handler != SIG_IGN)
            if (sigaction(SIGQUIT, &sa, NULL) == -1)
                errExit("sigaction");

        if (sigaction(SIGINT, NULL, &prev) == -1)
            errExit("sigaction");
        if (prev.sa_handler != SIG_IGN)
            if (sigaction(SIGINT, &sa, NULL) == -1)
                errExit("sigaction");

        sa.sa_handler = tstpHandler;

        if (sigaction(SIGTSTP, NULL, &prev) == -1)
            errExit("sigaction");
        if (prev.sa_handler != SIG_IGN)
            if (sigaction(SIGTSTP, &sa, NULL) == -1)
                errExit("sigaction");
    } else {                            /* Use raw mode */
        if (ttySetRaw(STDIN_FILENO, &userTermios) == -1)
            errExit("ttySetRaw");
    }

    sa.sa_handler = handler;
    if (sigaction(SIGTERM, &sa, NULL) == -1)
        errExit("sigaction");

    setbuf(stdout, NULL);               /* Disable stdout buffering */

    for (;;) {                          /* Read and echo stdin */
        n = read(STDIN_FILENO, &ch, 1);
        if (n == -1) {
            errMsg("read");
            break;
        }

        if (n == 0)                     /* Can occur after terminal disconnect */
            break;

        if (isalpha((unsigned char) ch))        /* Letters --> lowercase */
            putchar(tolower((unsigned char) ch));
        else if (ch == '\n' || ch == '\r')
            putchar(ch);
        else if (iscntrl((unsigned char) ch))
            printf("^%c", ch ^ 64);     /* Echo Control-A as ^A, etc. */
        else
            putchar('*');               /* All other chars as '*' */

        if (ch == 'q')                  /* Quit loop */
            break;
    }

    if (tcsetattr(STDIN_FILENO, TCSAFLUSH, &userTermios) == -1)
        errExit("tcsetattr");
    exit(EXIT_SUCCESS);
}

 

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