From e26d8e0e1ba7336c8a4e3e26f3e06d69579c005a Mon Sep 17 00:00:00 2001
From: DTB <trinity@trinity.moe>
Date: Sun, 21 Apr 2024 06:21:15 -0600
Subject: [PATCH] pg(1): import from trinity/src

---
 Makefile  |  8 ++++++--
 docs/pg.1 | 24 ++++++++++++++++++++++++
 src/pg.c  | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 86 insertions(+), 2 deletions(-)
 create mode 100644 docs/pg.1
 create mode 100644 src/pg.c

diff --git a/Makefile b/Makefile
index 68efd20..c7dd463 100644
--- a/Makefile
+++ b/Makefile
@@ -102,11 +102,15 @@ mm: build/bin/mm
 build/bin/mm: src/mm.c build
 	$(CC) $(CFLAGS) -o $@ src/mm.c
 
-
 .PHONY: npc
 npc: build/bin/npc
 build/bin/npc: src/npc.c build
-	$(CC) $(CFLAGAS) -o $@ src/npc.c
+	$(CC) $(CFLAGS) -o $@ src/npc.c
+
+.PHONY: pg
+pg: build/bin/pg
+build/bin/pg: src/pg.c build
+	$(CC) $(CFLAGS) -o $@ src/pg.c
 
 .PHONY: rpn
 rpn: build/bin/rpn
diff --git a/docs/pg.1 b/docs/pg.1
new file mode 100644
index 0000000..e0f1f99
--- /dev/null
+++ b/docs/pg.1
@@ -0,0 +1,24 @@
+.TH P 1
+
+.SH NAME
+
+pg \(en paginate
+
+.SH DESCRIPTION
+
+Pg prints standard input to standard output, pausing every 22 lines and waiting
+for a line feed from the tty before continuing.
+
+.SH DIAGNOSTICS
+
+Pg returns an unsuccessful exit code if the tty couldn't be opened or if pg was
+invoked incorrectly (with any arguments).
+
+.SH RATIONALE
+
+Plan 9 from Bell Labs had p(1), a similar "cooked"-mode paginator (as opposed
+to "raw" mode, which a vast majority of paginators use).
+
+.SH SEE ALSO
+
+more(1)
diff --git a/src/pg.c b/src/pg.c
new file mode 100644
index 0000000..5cb02a1
--- /dev/null
+++ b/src/pg.c
@@ -0,0 +1,56 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#if !defined EX_USAGE || !defined EX_SOFTWARE
+#	include <sysexits.h>
+#endif
+
+/* Done while looking at plan9ports' src/cmd/p.c.
+ * Taken from plan9 are the interface (minus p(1)'s shell escaping and the
+ * ability to page multiple files) and the practice of reading /dev/tty to get
+ * keyboard input without going through stdin. Also, a newline is now printed
+ * before querying the keyboard. */
+
+static size_t l = 22; /* plan9 default */
+
+static char *program_name = "p";
+
+static int print_lines(FILE *f, size_t l){
+	int c;
+
+	while((c = getc(f)) != EOF)
+		if((c = putc(c, stdout)) == EOF || (l -= (c == '\n')) == 0)
+			break;
+
+	return c;
+}
+
+int main(int argc, char *argv[]){
+	unsigned char cmd[99+1];
+	char *p;
+	FILE *t;
+
+	if(argc == 0)
+		argv = &program_name;
+
+	if(argc > 1){
+		fprintf(stderr, "Usage: %s\n", argv[0]);
+		return EX_USAGE;
+	}
+
+	if((t = fopen("/dev/tty", "rb")) == NULL){
+		fprintf(stderr, "%s: Could not open /dev/tty\n", argv[0]);
+		return EX_SOFTWARE;
+	}
+
+	while(print_lines(stdin, l) != EOF){
+		fgets(cmd, (sizeof cmd) / (sizeof *cmd), t);
+		for(p = cmd; *p != '\0' && strchr(" \t", *p) != NULL; ++p);
+		if(feof(t) || (*p | 32) == 'q')
+			break;
+	}
+
+exit:	fclose(t);
+	return 0;
+}