pty/unbuffer.c

This is pty/unbuffer.c, an example program file from the book, The Linux Programming Interface.

This file is not printed in the book; it is the solution to Exercise 64-7 (page 1398).

The source code file is copyright 2010, Michael Kerrisk, and is licensed under the GNU Affero General Public License, version 3.

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.

  Cover of The Linux Programming Interface

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

/* unbuffer.c

   Use a pseudoterminal to circumvent the block buffering performed by the
   stdio library when standard output is redirected to a file or pipe.
   When a program is started using 'unbuffer', its output is redirected to
   a pseudoterminal, and is consequently line-buffered.

   Usage: unbuffer prog [arg ...]
*/
#include <termios.h>
#if ! defined(__hpux)
/* HP-UX 11 doesn't have this header file */
#include <sys/select.h>
#endif
#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 */
ttyReset(void)
{
    if (tcsetattr(STDIN_FILENO, TCSANOW, &ttyOrig) == -1)
        errExit("tcsetattr");
}
int
main(int argc, char *argv[])
{
    char slaveName[MAX_SNAME];
    int masterFd;
    fd_set inFds;
    char buf[BUF_SIZE];
    ssize_t numRead;
    struct winsize ws;

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

    if (tcgetattr(STDIN_FILENO, &ttyOrig) == -1)
        errExit("tcgetattr");
    if (ioctl(STDIN_FILENO, TIOCGWINSZ, (char *) &ws) < 0)
        errExit("TIOCGWINSZ error");

    /* 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. */

    switch (ptyFork(&masterFd, slaveName, MAX_SNAME, &ttyOrig, &ws)) {
    case -1:
        errExit("ptyFork");

    case 0:     /* Child executes command given in argv[1]... */
        execvp(argv[1], &argv[1]);
        errExit("execvp");

    default:    /* Parent relays data between terminal and pty master */

        /* 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)
            errExit("atexit");

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

        for (;;) {
            FD_ZERO(&inFds);
            FD_SET(STDIN_FILENO, &inFds);
            FD_SET(masterFd, &inFds);
            if (select(masterFd + 1, &inFds, NULL, NULL, NULL) == -1)
                errExit("select");

            if (FD_ISSET(STDIN_FILENO, &inFds)) {
                numRead = read(STDIN_FILENO, buf, BUF_SIZE);
                if (numRead <= 0)
                    exit(EXIT_SUCCESS);

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

            if (FD_ISSET(masterFd, &inFds)) {
                numRead = read(masterFd, buf, BUF_SIZE);
                if (numRead <= 0)
                    exit(EXIT_SUCCESS);

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

 

Download pty/unbuffer.c