From fdda5c19432ad7dc7f1b1823a058f6444f463372 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Tue, 3 May 2022 20:34:41 -0700
Subject: New -g option to pre-load the grep stack.

---
 pw.1 | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 pw.c | 32 +++++++++++++++++++++++++++++++-
 2 files changed, 86 insertions(+), 1 deletion(-)

diff --git a/pw.1 b/pw.1
index e423baa..15f3d2f 100644
--- a/pw.1
+++ b/pw.1
@@ -588,6 +588,61 @@ that is the default, this option has no effect unless it appears after a
 .B -E
 option.
 
+.IP "\fB-g\fP [\fB!\fP]\fIpattern\fP"
+
+Push
+.I pattern
+onto the grep stack as if using the
+.B :v
+or
+.B :g
+commands, but prior to startup, and hence prior to reading any input.
+
+For more detail, see the
+.B :g
+and
+.B :v
+run-time commands.
+
+A leading
+.B !
+before the pattern indicates inversion, like what is arranged by the
+.B :v
+command. Similarly to the convention in the trigger command syntax,
+to specify a non-inverted pattern which starts with a literal
+.B !
+character, precede that
+.B !
+character with a backslash. This convention is part of the
+.B -g
+option's argument syntax, and not a regular expression escape sequence,
+and is not recognized other than before a non-inverted pattern.
+
+If the
+.B -g
+option is used one or more times, the status display will show
+.B GREP
+followed by the patterns enclosed in parentheses, as usual.
+Patterns pushed by
+.B -g
+may be removed interactively with the
+.B :r
+command.
+
+Whether the
+.I pattern
+argument of a
+.B -g
+is compiled as a BRE or ERE depends on whether a
+.B -B
+or
+.B -E
+option more recently appeared before that
+.B -g
+option. If neither option is used, then
+.I pattern
+is interpreted as a BRE.
+
 .SH ENVIRONMENT
 
 .I pw
diff --git a/pw.c b/pw.c
index c9d9bbf..8da30a4 100644
--- a/pw.c
+++ b/pw.c
@@ -245,6 +245,7 @@ static void usage(void)
           "-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"
+          "-g [!]pattern   add pattern to grep stack; ! inverts.\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"
@@ -725,7 +726,7 @@ int main(int argc, char **argv)
     }
   }
 
-  while ((opt = getopt(argc, argv, "n:i:l:dEB")) != -1) {
+  while ((opt = getopt(argc, argv, "n:i:l:dEBg:")) != -1) {
     switch (opt) {
     case 'n':
       {
@@ -761,6 +762,35 @@ int main(int argc, char **argv)
     case 'B':
       regex_flags = 0;
       break;
+    case 'g':
+      {
+        grep *gr = &grepstack[ngrep];
+        char *pat = optarg;
+        int inv = 0;
+
+        if (ngrep >= maxgrep) {
+          error("too many patterns specified with -g\n");
+          return EXIT_FAILURE;
+        }
+
+        if (*pat == '!') {
+          inv = 1;
+          pat++;
+        } else if (strncmp(pat, "\\!", 2) == 0) {
+          pat++;
+        }
+
+        if ((grinit(gr, dsdup(pat), inv, dsdrop)) != 0) {
+          char grmsg[cmdsize];
+          grerrstr(gr, grmsg, sizeof grmsg);
+          error("-%c option: bad pattern %s: %s\n", opt, pat, grmsg);
+          return EXIT_FAILURE;
+        }
+
+        ngrep++;
+        stat |= stat_grep;
+      }
+      break;
     default:
       usage();
     }
-- 
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