Makefile

@@ -32,7 +32,7 @@ RUSTLIBS = --extern getopt=build/o/libgetopt.rlib \
 CFLAGS += -I$(SYSEXITS)
 
 .PHONY: all
-all: dj false fop hru intcmp mm npc rpn scrut str strcmp swab true
+all: dj false fop hru intcmp mm npc rpn scroll scrut str strcmp swab true
 
 # keep build/include until bindgen(1) has stdin support
 # https://github.com/rust-lang/rust-bindgen/issues/2703
@@ -120,7 +120,12 @@ build/bin/mm: src/mm.rs build rustlibs
 .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: scroll
+scroll: build/bin/scroll
+build/bin/scroll: src/scroll.c build
+	$(CC) $(CFLAGS) -o $@ src/scroll.c
 
 .PHONY: rpn
 rpn: build/bin/rpn

docs/scroll.1

@@ -0,0 +1,52 @@
+.\" Copyright (c) 2024 DTB <trinity@trinity.moe>
+.\" Copyright (c) 2024 Emma Tebibyte <emma@tebibyte.media>
+.\"
+.\" This work is licensed under CC BY-SA 4.0. To see a copy of this license,
+.\" visit <http://creativecommons.org/licenses/by-sa/4.0/>.
+.\"
+.TH PG 1 2024-07-31 "Harakit X.X.X"
+.SH NAME
+scroll \(en present output
+.\"
+.SH SYNOPSIS
+
+scroll
+.RB ( -p
+.RB [ prompt ])
+.\"
+.SH DESCRIPTION
+
+Print standard input to standard output, accepting commands between pages.
+.\"
+.SH OPTIONS
+
+.IP -p
+Replace the default prompt (\(lq: \(rq) with the option argument.
+.\"
+.SH DIAGNOSTICS
+
+In the event of an error, a debug message will be printed and the program will
+exit with the appropriate
+.BR sysexits.h (3)
+error code.
+.\"
+.SH RATIONALE
+
+Plan 9 from Bell Labs had
+.BR p (1),
+a similar \(lqcooked\(rq-mode paginator (as opposed to \(lqraw\(rq mode, which a
+vast majority of paginators use).
+.\"
+.SH AUTHOR
+
+Written by DTB
+.MT trinity@trinity.moe
+.ME .
+.\"
+.SH COPYRIGHT
+
+Copyright \(co 2024 DTB. License AGPLv3+: GNU AGPL version 3 or later
+<https://gnu.org/licenses/agpl.html>.
+.\"
+.SH SEE ALSO
+.BR more (1p)

src/scroll.c

@@ -0,0 +1,288 @@
+/*
+ * Copyright (c) 2024 DTB <trinity@trinity.moe>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ *
+ * This program is free software: you can redistribute it and/or modify it under
+ * the terms of the GNU Affero General Public License as published by the Free
+ * Software Foundation, either version 3 of the License, or (at your option) any
+ * later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program. If not, see https://www.gnu.org/licenses/.
+ */
+
+#include <assert.h> /* assert(3) */
+#include <errno.h> /* errno */
+#include <stdbool.h> /* bool */
+#include <stdio.h> /* fclose(3), feof(3), fgetc(3), fgets(3), fopen(3),
+                    * fprintf(3), fputc(3), perror(3), stderr, stdin, stdout,
+                    * EOF, FILE, NULL */
+#include <stdlib.h> /* size_t */
+#include <string.h> /* strchr(3), strcmp(3) */
+#include <unistd.h> /* getopt(3) */
+
+/* Commands start with cmd_. They take an argc and NULL-terminated argv, like
+ * main, and return a status from <sysexits.h>. Return values other than EX_OK
+ * and EX_USAGE cause pg(1) to exit with that value, except EX_UNAVAILABLE,
+ * which causes pg(1) to exit with the status EX_OK. */
+#include <sysexits.h>
+
+#define CMDLINE_MAX 99+1 /* Maximum length of command line. */
+
+static char *whitespace = " \n\r\t\v";
+
+//static
+struct Tube {
+	char *name;   // command line
+	FILE *in;     // process stdin
+	FILE *out;    // process stdoout
+	size_t index; // in pipeline
+};
+
+static struct {
+	size_t quantity;
+	enum { LINES = 0, BYTES = 1 } type;
+} default_page_unit = { 22, LINES } /* Plan 9 default */;
+
+static char *prompt = ": ";
+static char *program_name = "pg";
+
+static char *
+permute_out(char *s, size_t i) {
+	for (
+		;
+		s[i] != '\0';
+		s[i] = s[i + 1], ++i
+	);
+
+	return s;
+}
+
+/* strtok(3p), but supports double-quotes and escapes (but only for escaping
+ * quotes).  Unmatched quotes in str are considered literal. The behavior of
+ * strtok_quoted when '\'', '"', or '\\' are in sep is undefined. Use of UTF-8
+ * separators with strtok_quoted is undefined. */
+static char *
+strtok_quoted(char *str, char *sep) {
+	static char *s;
+
+	if (str != NULL) { s = str; }
+
+	while (strchr(sep, *s) != NULL) { // skip beginning whitespace
+		if(*++s == '\0') { return NULL; } // no remaining except seps
+	}
+
+	{
+		bool in_escape = 0; // previous char was '\\'
+		char quote = '\0';  // quotation mark used, or '\0' if none
+
+		for (int i = 0; s[i] != '\0'; ++i)
+			switch (s[i]) {
+				case '\\':
+					// if literal "\\", permute out a backslash
+					if (in_escape) { (void)permute_out(s, i--); }
+					in_escape = !in_escape;
+					break;
+				case '\'': case '"':
+					if (in_escape) { // \"
+						s[i] = s[i - 1];
+						(void)permute_out(s, i--); // permute out backslash
+					} else if (s[i] == quote) {
+						quote = '\0';
+						(void)permute_out(s, i--); // second quote
+					} else {
+						quote = s[i];
+						if (strchr(&s[i + 1], quote) != NULL) { // has a match
+							(void)permute_out(s, i--); // permute out lquote
+						}
+					}
+					break;
+				case '\0': return s;
+				default:
+					if (!in_escape
+					    	&& quote == '\0'
+					    	&& (strchr(sep, s[i]) != NULL || s[i] == '\0')) {
+						char *t; // start of current token
+
+						t = s;
+						s = s[i] != '\0'
+							? &t[i + 1] // store start of next token,
+							: &t[i];    // or the address of the nul if found
+						s[i] = '\0'; // NUL terminate current token
+
+						return t;
+					}
+			}
+	}
+
+	return s;
+}
+
+/* Page at most l bytes from f without consideration of a buffer (print them to
+ * stdout). */
+static int
+pg_b_u(FILE *f, size_t l) {
+	int c;
+
+	while ((c = fgetc(f)) != EOF) {
+		if ((c = fputc(c, stdout)) == EOF || --l == 0) { break; }
+	}
+
+	return c;
+}
+
+/* Page at most l lines, which are lengths of characters terminated by nl, from
+ * f without consideration of a buffer (print them to stdout). */
+static int
+pg_l_u(FILE *f, size_t l, char nl) {
+	int c;
+
+	while ((c = fgetc(f)) != EOF) {
+		if ((c = fputc(c, stdout)) == EOF || (l -= (c == nl)) == 0) { break; }
+	}
+
+	return c;
+}
+
+static int
+cmd_quit(int argc, char **argv, char **envp) { return EX_UNAVAILABLE; }
+
+static int
+cmd_default_page(int argc, char **argv, char **envp) {
+	if (argc > 1) { return EX_USAGE; } // should be impossible
+	else if (default_page_unit.type == BYTES) {
+		return pg_b_u(stdin, default_page_unit.quantity) == EOF
+			? EX_UNAVAILABLE
+			: EX_OK;
+	} else if (default_page_unit.type == LINES) {
+		return pg_l_u(stdin, default_page_unit.quantity, '\n') == EOF
+			? EX_UNAVAILABLE
+			: EX_OK;
+	} else { return EX_SOFTWARE; }
+}
+
+static int
+cmd_page_down_lines(int argc, char **argv, char **envp) {
+	switch (argc) {
+		case 1: return cmd_default_page(argc, argv, envp);
+		case 2: /* not implemented */
+		default:
+			(void)fprintf(stderr, "Usage: %s" /*" (lines)"*/ "\n", argv[0]);
+			return EX_USAGE;
+	}
+}
+
+/* A CmdMap must be NULL-terminated. */
+static struct CmdMap{ char *name; int (*fn)(int, char **, char **); }
+builtins[] = {
+	/* don't make the user feel trapped */
+	{ ":q", cmd_quit }, { ":q!", cmd_quit },
+	{ "exit", cmd_quit }, { "q", cmd_quit }, { "Q", cmd_quit },
+	{ "quit", cmd_quit }, { "ZZ", cmd_quit },
+	
+	{ NULL, NULL }
+};
+
+#define ARGV_MAX 10
+/* Find and execute the command in the command map, given a corresponding
+ * command line. */
+static int
+cmdline_exec(struct CmdMap *map, char *cmdline, char **envp) {
+	static int argc;
+	static char *argv[ARGV_MAX];
+
+	if ((argv[(argc = 0)] = strtok_quoted(cmdline, whitespace)) == NULL) {
+		while (cmdline[0] != '\0') { cmdline = &cmdline[1]; }
+		argv[argc] = cmdline;
+		argv[++argc] = NULL;
+	} else {
+		while (
+			(argv[++argc] = strtok_quoted(NULL, whitespace)) != NULL
+			&& argc < ARGV_MAX
+		);
+	}
+
+	for (; map->name != NULL; map = &map[1]) {
+		if(strcmp(map->name, argv[0]) == 0) {
+			return map->fn(argc, argv, envp);
+		}
+	}
+
+	(void)fprintf(stderr, "%s: %s: not found\n", program_name, argv[0]);
+	return EX_USAGE;
+}
+
+static int
+ioerr(char *argv0) {
+	perror(argv0);
+
+	return EX_IOERR;
+}
+
+static int
+usage(char *argv0) {
+	(void)fprintf(stderr, "Usage: %s [-p prompt]\n", argv0);
+
+	return EX_USAGE;
+}
+
+int main(int argc, char *argv[]) {
+	unsigned char cmd[CMDLINE_MAX];
+	FILE *t;
+
+	if (argc > 0) {
+		int c;
+
+		program_name = argv[0];
+
+		while ((c = getopt(argc, argv, "p:")) != -1) {
+			switch (c) {
+				case 'p': prompt = optarg; break;
+				default:  return usage(program_name);
+			}
+		}
+	}
+
+	if (argc > optind) { return usage(program_name); }
+
+
+	if ((t = fopen("/dev/tty", "rb")) == NULL) {
+		perror(program_name);
+
+		return EX_OSERR;
+	}
+
+	for (;;) {
+		if (fputs(prompt, stderr) == EOF) { return ioerr(program_name); }
+
+		// if the line...
+		if (fgets((char *)cmd, (sizeof cmd) / (sizeof *cmd), t) != NULL) {
+			if (strchr((char *)cmd, '\n') == NULL) { // was taken incompletely
+				int c;
+
+				while ((c = fgetc(t)) != '\n') { // ...fast-forward stream
+					if (c == EOF) { break; }
+				}
+			}
+		} else { fputc('\n', stdout); } // EOF at start of line; finish prompt
+
+		if (feof(t)) { return EX_OK; }
+
+		{
+			int r;
+
+			switch ((r = cmdline_exec(builtins, (char *)cmd, NULL))){
+				case EX_OK: case EX_USAGE: break;
+				case EX_UNAVAILABLE: return EX_OK;
+				default: return r;
+			}
+		}
+	}
+
+	/* UNREACHABLE */ assert(0);
+}