pty/script.c

+/* 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>
+#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];
     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)
         errExit("tcgetattr");
     if (ioctl(STDIN_FILENO, TIOCGWINSZ, &ws) < 0)
         errExit("ioctl-TIOCGWINSZ");
 
+    /* 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)
         errExit("ptyFork");
 
     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)
         errExit("atexit");
 
+    /* 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_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)) {   /* stdin --> pty */
             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)) {      /* pty --> stdout+file */
             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)");
             if (write(scriptFd, buf, numRead) != numRead)
                 fatal("partial/failed write (scriptFd)");
         }
     }
 }