Remove non-interactive mode.

2 files changed, 92 insertions, 74 deletions

diff --git a/pw.1 b/pw.1
index 167ec0d..00e106b 100644
--- a/pw.1
+++ b/pw.1
@@ -34,34 +34,15 @@ command | pw [-i interval] [-l interval] [-n number-of-lines] [-dEB]
 
 .SH DESCRIPTION
 .I pw
-stands for Pipe Watch. This is a utility which continuously reads textual input
-from a pipe or pipe-like source, and maintains a dynamic display of the
-most recently read
-.I N
-lines.
-
-If
-.I pw
-is invoked such that its standard input is a TTY, it simply reads lines
-and prints them in its characteristic way, with control characters replaced by
-caret codes, until end-of-file is encountered. Long lines aren't clipped,
-and there is no interactive mode.
-
-The intended use of
-.I pw
-is that its standard input is a pipe, such as the output of another command,
-or a pipe-like device such as a socket or whatever.
-In this situation,
-.I pw
-expects to be executed in a TTY session in which a
-.B /dev/tty
-device can be opened, for the purposes of obtaining interactive input.
-The remaining description pertains to this interactive mode.
+stands for Pipe Watch, a utility that continuously reads lines of
+text from a pipe or pipe-like source, passes them through a FIFO buffer, and
+maintains a display based on the occasional sampling the contents of the
+FIFO buffer, with useful features such as triggering and filtering.
 
-In interactive mode,
+Upon successful startup,
 .I pw
-simultaneously monitors its standard input for the arrival of new data,
-as well as the TTY for interactive commands.
+simultaneously monitors its standard input for the
+arrival of new data, as well as the TTY for interactive commands.
 Lines from standard input are placed into a FIFO buffer.
 While the FIFO buffer is not yet full, lines are displayed immediately.
 After the FIFO buffer fills up with the specified number of lines
@@ -69,13 +50,27 @@ After the FIFO buffer fills up with the specified number of lines
 .B -n
 option) then
 .I pw
-transitions into a mode in which, old lines are bumped from the tail of the
-FIFO as new ones are added to the head, and refresh operations are required in
-order to display the current FIFO contents.
+transitions into the free-running mode in which, old lines are removed from the
+tail of the FIFO as new ones are added to the head, and the display is no
+longer refreshed for every new line arriving into the FIFO.
 
-The display only refreshes with the latest FIFO data when
+In free-running mode, the display is automatically refreshed with the latest
+FIFO data only if:
 .IP 1.
-there is some keyboard activity from the terminal; or
+suspended mode is not in effect; and
+.IP 2.
+trigger mode is not in effect; and
+.IP 3.
+.I pw
+isn't executing in the background (see the
+.B Ctrl-Z
+command).
+.PP
+
+When the above conditions do not hold, and thus the display is being
+automatically refreshed, it is refreshed at these times:
+.IP 1.
+when there is some keyboard activity from the terminal; or
 .IP 2.
 when the interval period has expired
 without new input having been seen; or else
@@ -83,12 +78,22 @@ without new input having been seen; or else
 whenever the long period elapses.
 .PP
 
-In other words, while the pipe is spewing, and there is
-no keyboard input, the display is updated infrequently, only according to the
-long interval.
+In other words, while the input is rapidly producing data, and there is no
+keyboard input, the display is updated infrequently, only according to the long
+interval.
+
+If
+.I pw
+is executing in the foreground, and if display updates aren't suspended, and if
+trigger mode is effect, then the display updates automatically only when a
+trigger is activated by a pattern match on the FIFO contents. Trigger mode is
+activated using the
+.B >
+and
+.B ?
+commands below.
 
-The display is also updated when standard input indicates end-of-data.
-In this situation,
+When standard input indicates end-of-data.
 .I pw
 terminates, unless the
 .B -d
@@ -128,10 +133,9 @@ portion appears delimited by
 
 .SH COMMANDS
 
-When
+While reading data from standard input,
 .I pw
-enters closed loop operation, the following single-key commands are
-available.
+monitors the TTY for input, providing the following commands.
 
 The commands may be prefixed by a numeric argument, which is ignored by
 commands to which it is not applicable. The numeric argument is specified by
@@ -581,6 +585,27 @@ that is the default, this option has no effect unless it appears after a
 .B -E
 option.
 
+.SH ENVIRONMENT
+
+.I pw
+ignores the
+.B TERM
+environment variable, requiring an ANSI terminal.
+
+.I pw
+requires the following conditions to hold in regard to its execution environment,
+otherwise it terminates with an error diagnostic:
+.IP 1.
+Standard output must be a TTY device.
+.IP 2.
+Standard input is either not a TTY device, or else not the same TTY device
+as standard output.
+.IP 3.
+It must be possible to open the
+.B /dev/tty
+device, which is the same TTY as standard output.
+.PP
+
 .SH TERMINATION STATUS
 
 If
diff --git a/pw.c b/pw.c
index 379bc8a..b8f3fa3 100644
--- a/pw.c
+++ b/pw.c
@@ -233,26 +233,6 @@ static char *addchesc(char *line, int ch)
   return line;
 }
 
-static char *getln(FILE *stream)
-{
-  char *line = 0;
-
-  for (;;) {
-    int ch = getc(stream);
-
-    if (ch == EOF)
-      return line;
-
-    if (ch == '\n') {
-      if (line)
-        return line;
-      return addch(line, 0);
-    }
-
-    line = addchesc(line, ch);
-  }
-}
-
 static void usage(const char *name)
 {
   fprintf(stderr,
@@ -702,7 +682,8 @@ int main(int argc, char **argv)
   FILE *tty = fopen("/dev/tty", "r+");
   int maxlines = 15, nlines = 0, maxed = 0;
   int opt;
-  int fd = fileno(stdin);
+  int ifd = fileno(stdin);
+  int ofd = fileno(stdout);
   int ttyfd = tty ? fileno(tty) : -1;
   char **circbuf;
   struct termios tty_saved, tty_new;
@@ -719,11 +700,32 @@ int main(int argc, char **argv)
   static struct sigaction sa;
 #endif
 
-  if (fd < 0)
-    panic("unable to obtain input file descriptor");
+  if (ifd < 0)
+    panic("unable to obtain input file descriptor\n");
+
+  if (ofd < 0)
+    panic("unable to obtain input file descriptor\n");
+
+  if (!isatty(ofd))
+    error("standard output must be a TTY\n");
 
   if (ttyfd < 0)
-    panic("unable to open /dev/tty");
+    panic("unable to open /dev/tty\n");
+
+  {
+    pid_t ogrp = tcgetpgrp(ofd);
+    pid_t igrp = tcgetpgrp(ifd);
+    pid_t tgrp = tcgetpgrp(ttyfd);
+
+    if (ogrp < 0)
+      error("standard output isn't a job control TTY\n");
+
+    if (ogrp != tgrp)
+      error("/dev/tty isn't the same as the standard output TTY\n");
+
+    if (igrp == ogrp)
+      error("standard input and standard output are the same TTY\n");
+  }
 
   while ((opt = getopt(argc, argv, "n:i:l:dEB")) != -1) {
     switch (opt) {
@@ -774,15 +776,6 @@ int main(int argc, char **argv)
   if ((snapshot[0] = calloc(sizeof *snapshot[0], maxlines)) == 0)
     panic("out of memory");
 
-  if (isatty(fd)) {
-    while ((line = getln(stdin))) {
-      puts(line);
-      dsdrop(line);
-    }
-
-    return 0;
-  }
-
   if (ioctl(ttyfd, TIOCGWINSZ, &ws) == 0 && ws.ws_row != 0) {
     if (maxlines >= ws.ws_row) {
       maxlines = ws.ws_row - 1;
@@ -804,7 +797,7 @@ int main(int argc, char **argv)
 
   setvbuf(tty, NULL, _IONBF, 0);
 
-  if (fcntl(fd, F_SETFL, O_NONBLOCK) < 0)
+  if (fcntl(ifd, F_SETFL, O_NONBLOCK) < 0)
     panic("unable to set stdin nonblocking");
 
   if (!isbkgnd(stdout))
@@ -826,7 +819,7 @@ int main(int argc, char **argv)
     int force = 0, nfds = 2, pollms = poll_interval;
     struct pollfd pe[2] = {
       { .fd = ttyfd, .events = POLLIN | POLLHUP | POLLERR },
-      { .fd = fd, .events = POLLIN | POLLHUP | POLLERR },
+      { .fd = ifd, .events = POLLIN | POLLHUP | POLLERR },
     };
 
     if ((stat & stat_eof) == 0) {