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 2024, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

This page shows the "distribution" or "book" version of the file (why are there two versions?), or the differences between the two versions. You can switch between the views using the tabs below.

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.

 

Download tty/test_tty_functions.c

  Cover of The Linux Programming Interface

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

#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);
}

 

Download tty/test_tty_functions.c

Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.

Valid XHTML 1.1