From e61a2da6f7509d0ce2766bf46095279036646329 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Mon, 2 May 2022 22:31:01 -0700
Subject: Relax restrictions on stdout; improve error reporting.

---
 pw.1 | 10 ++++------
 pw.c | 46 +++++++++++++++++++++++-----------------------
 2 files changed, 27 insertions(+), 29 deletions(-)

diff --git a/pw.1 b/pw.1
index 00e106b..4da72ad 100644
--- a/pw.1
+++ b/pw.1
@@ -596,14 +596,12 @@ environment variable, requiring an ANSI terminal.
 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.
+device,
+.IP 2.
+Standard input is either not a TTY device, or else not the same TTY device as
+.BR /dev/tty .
 .PP
 
 .SH TERMINATION STATUS
diff --git a/pw.c b/pw.c
index b8f3fa3..a288d9f 100644
--- a/pw.c
+++ b/pw.c
@@ -93,6 +93,7 @@ typedef struct dstr {
 
 #define dstr_of(str) ((dstr *) ((str) - sizeof (dstr)))
 
+static char *pw_name;
 static int poll_interval = 1000;
 static int long_interval = 10000;
 static int regex_flags = 0;
@@ -117,6 +118,7 @@ static void panic(const char *fmt, ...)
 {
   va_list vl;
   va_start (vl, fmt);
+  fprintf(stderr, "%s: ", pw_name);
   vfprintf(stderr, fmt, vl);
   abort();
 }
@@ -126,8 +128,8 @@ static void error(const char *fmt, ...)
 {
   va_list vl;
   va_start (vl, fmt);
+  fprintf(stderr, "%s: ", pw_name);
   vfprintf(stderr, fmt, vl);
-  exit(EXIT_FAILURE);
 }
 
 static char *dsref(char *str)
@@ -233,16 +235,22 @@ static char *addchesc(char *line, int ch)
   return line;
 }
 
-static void usage(const char *name)
+static void usage(void)
 {
   fprintf(stderr,
-          "\nUsage: %s [options]\n\n"
+          "\nUsage: <command> | %s [options]\n\n"
           "-i realnum      poll interval (s)\n"
           "-l realnum      long update interval (s)\n"
           "-n integer      display size (# of lines)\n"
-          "-d              do not quit on end-of-input\n\n"
+          "-d              do not quit on end-of-input\n"
+          "-E              treat regular expressions as extended\n"
+          "-B              treat regular expressions as basic (default)\n\n"
+          "<command> represents an arbitrary command that generates the\n"
+          "output to be monitored by %s.\n\n"
+          "Standard input must be redirected; it cannot be the same device\n"
+          "as the controlling tty (/dev/tty) of the terminal session.\n\n"
           "For a full description, see the manual page.\n\n",
-          name);
+          pw_name, pw_name);
   exit(EXIT_FAILURE);
 }
 
@@ -683,7 +691,6 @@ int main(int argc, char **argv)
   int maxlines = 15, nlines = 0, maxed = 0;
   int opt;
   int ifd = fileno(stdin);
-  int ofd = fileno(stdout);
   int ttyfd = tty ? fileno(tty) : -1;
   char **circbuf;
   struct termios tty_saved, tty_new;
@@ -700,31 +707,22 @@ int main(int argc, char **argv)
   static struct sigaction sa;
 #endif
 
-  if (ifd < 0)
-    panic("unable to obtain input file descriptor\n");
+  pw_name = argv[0] ? argv[0] : "pw";
 
-  if (ofd < 0)
+  if (ifd < 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\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");
+    if (igrp == tgrp) {
+      error("standard input cannot be the TTY used for display\n");
+      usage();
+    }
   }
 
   while ((opt = getopt(argc, argv, "n:i:l:dEB")) != -1) {
@@ -764,12 +762,14 @@ int main(int argc, char **argv)
       regex_flags = 0;
       break;
     default:
-      usage(argv[0]);
+      usage();
     }
   }
 
-  if (maxlines <= 0 || maxlines > 1000)
+  if (maxlines <= 0 || maxlines > 1000) {
     error("%d is an unreasonable number of lines to display\n", maxlines);
+    return EXIT_FAILURE;
+  }
 
   if ((circbuf = calloc(sizeof *circbuf, maxlines)) == 0)
     panic("out of memory");
-- 
cgit v1.2.3