pg(1): start work on a quoted strtok(3) and internal environment

Makefile

@@ -9,13 +9,23 @@
 # notice are preserved.  This file is offered as-is, without any warranty.
 
 .POSIX:
+
+# if using BSD make(1), remove these pragmas because they break it
 .PRAGMA: posix_202x # future POSIX standard support à la pdpmake(1)
 .PRAGMA: command_comment # breaks without this?
 
-PREFIX=/usr/local
+DESTDIR ?= dist
+PREFIX ?= /usr/local
 
-CC=cc
+SYSEXITS != printf '\043include <sysexits.h>\n' | cpp -M - | sed 's/ /\n/g' \
-RUSTC=rustc
+	| sed -n 's/sysexits\.h//p' || printf 'include\n'
+
+CC ?= cc
+RUSTC ?= rustc
+RUSTLIBS = --extern getopt=build/o/libgetopt.rlib \
+	--extern sysexits=build/o/libsysexits.rlib \
+	--extern strerror=build/o/libstrerror.rlib
+CFLAGS += -I$(SYSEXITS)
 
 .PHONY: all
 all: dj false fop hru intcmp mm npc rpn scrut str strcmp swab true
@@ -27,36 +37,40 @@ build:
 
 .PHONY: clean
 clean:
-	rm -rf build/ dist/
+	rm -rf build dist
 
 dist: all
-	mkdir -p dist/bin dist/share/man/man1
+	mkdir -p $(DESTDIR)/$(PREFIX)/bin $(DESTDIR)/$(PREFIX)/share/man/man1
-	cp build/bin/* dist/bin/
+	cp build/bin/* $(DESTDIR)/$(PREFIX)/bin
-	cp docs/*.1 dist/share/man/man1/
+	cp docs/*.1 $(DESTDIR)/$(PREFIX)/share/man/man1
 
 .PHONY: install
 install: dist
-	mkdir -p $(PREFIX)
+	cp -r $(DESTDIR)/* /
-	cp -r dist/* $(PREFIX)/
 
 .PHONY: test
 test: build
 	tests/posix-compat.sh
 	$(RUSTC) --test src/getopt-rs/lib.rs -o build/test/getopt
 
-build/o/libsysexits.rlib: build
+.PHONY: rustlibs
+rustlibs: build/o/libsysexits.rlib build/o/libgetopt.rlib \
+	build/o/libstrerror.rlib
+
+build/o/libgetopt.rlib: build src/getopt-rs/lib.rs
+	$(RUSTC) $(RUSTFLAGS) --crate-type=lib --crate-name=getopt \
+		-o $@ src/getopt-rs/lib.rs
+
+build/o/libstrerror.rlib: build src/strerror.rs
+	$(RUSTC) $(RUSTFLAGS) --crate-type=lib -o $@ \
+		src/strerror.rs
+
+build/o/libsysexits.rlib: build $(SYSEXITS)sysexits.h
 	# bandage solution until bindgen(1) gets stdin support
-	printf '#define EXIT_FAILURE 1\n' | cat - include/sysexits.h \
+	printf '#define EXIT_FAILURE 1\n' | cat - $(SYSEXITS)sysexits.h \
 		> build/include/sysexits.h 
 	bindgen --default-macro-constant-type signed --use-core --formatter=none \
-		"$$(printf '#include <sysexits.h>\n' \
+		build/include/sysexits.h | $(RUSTC) $(RUSTFLAGS) --crate-type lib -o $@ -
-			| cpp -M -idirafter "build/include" - \
-			| sed 's/ /\n/g' | grep sysexits.h)" \
-		| $(RUSTC) $(RUSTFLAGS) --crate-type lib -o build/o/libsysexits.rlib -
-
-build/o/libgetopt.rlib: src/getopt-rs/lib.rs
-	$(RUSTC) $(RUSTFLAGS) --crate-type=lib --crate-name=getopt \
-		-o build/o/libgetopt.rlib src/getopt-rs/lib.rs
 
 .PHONY: dj
 dj: build/bin/dj
@@ -70,17 +84,13 @@ build/bin/false: src/false.c build
 
 .PHONY: fop
 fop: build/bin/fop
-build/bin/fop: src/fop.rs build build/o/libgetopt.rlib build/o/libsysexits.rlib
+build/bin/fop: src/fop.rs build rustlibs
-	$(RUSTC) $(RUSTFLAGS) --extern getopt=build/o/libgetopt.rlib \
+	$(RUSTC) $(RUSTFLAGS) $(RUSTLIBS) -o $@ src/fop.rs
-		--extern sysexits=build/o/libsysexits.rlib \
-		-o $@ src/fop.rs
 
 .PHONY: hru
 hru: build/bin/hru
-build/bin/hru: src/hru.rs build build/o/libgetopt.rlib build/o/libsysexits.rlib
+build/bin/hru: src/hru.rs build rustlibs 
-	$(RUSTC) $(RUSTFLAGS) --extern getopt=build/o/libgetopt.rlib \
+	$(RUSTC) $(RUSTFLAGS) $(RUSTLIBS) -o $@ src/hru.rs
-		--extern sysexits=build/o/libsysexits.rlib \
-		-o $@ src/hru.rs
 
 .PHONY: intcmp
 intcmp: build/bin/intcmp
@@ -92,18 +102,20 @@ 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
-build/bin/rpn: src/rpn.rs build build/o/libsysexits.rlib
+build/bin/rpn: src/rpn.rs build rustlibs
-	$(RUSTC) $(RUSTFLAGS) \
+	$(RUSTC) $(RUSTFLAGS) $(RUSTLIBS) -o $@ src/rpn.rs
-		--extern sysexits=build/o/libsysexits.rlib \
-		-o $@ src/rpn.rs
 
 .PHONY: scrut
 scrut: build/bin/scrut

docs/pg.1

@@ -0,0 +1,41 @@
+.\" Copyright (c) 2024 DTB <trinity@trinity.moe>
+.\"
+.\" 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
+
+.SH NAME
+
+pg \(en paginate
+
+.SH SYNOPSIS
+
+pg
+.RB ( -p
+.RB [ prompt ])
+
+.SH DESCRIPTION
+
+Pg prints standard input to standard output, accepting commands between pages.
+
+.SH OPTIONS
+
+.B -p
+.RS
+Replaces the default prompt (": ") with the next argument.
+.RE
+
+.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)

src/dj.c

@@ -46,11 +46,31 @@ struct Io{
 /* Additionally, the following global variables are used to store user options.
  */
 
+/* (-a)  */ static int align; /* Only the lower 8b are used but align is
+                               * negative if no alignment is being done. */
+
+/* (-c)  */ static int count; /* 0 if dj(1) runs until no more reads are
+                               * possible. */
+
 /* ASCII field separator delimited statistics */
             static char *fmt_asv   = "%d\037%d\036%d\037%d\035%d\036%d\034";
-
+/* human-readable statistics */
-/* (-H) Human-readable statistics */
             static char *fmt_human = "%d+%d > %d+%d; %d > %d\n";
+/* pointer to chosen formatting */
+/* (-H)  */ static char *fmt_output; /* fmt_asv (default) or fmt_human (-H) */
+
+/* (-dq) */ static char debug;       /*
+ *  -d  increments             dj -qq | 0 - no diagnostic output whatsoever
+ *   -q decrements             dj -q  | 1 - typical output without
+ *                                    |     notifications on partial reads or
+ *                                    |     writes
+ *                             dj     | 2 - typical output (default)
+ *                             dj -d  | 3 - verbose status messages */
+
+/* (-n)  */ static char noerror;     /* 0 - exits on partial reads or writes
+                                      *     (default)
+                                      * 1 - retries on partial reads/writes
+                                      *     (-n) */
 
 /* Non-configurable defaults. */
 #define bs_default 1024 /* GNU dd(1) default; twice POSIX but a neat 2^10 */
@@ -60,8 +80,19 @@ static char *stdout_name = "<stdout>";
 static int read_flags = O_RDONLY; /* These flags are consistent with Busybox */
 static int write_flags = O_WRONLY | O_CREAT; /* dd(1). */
 
+/* Macro to set defaults for user-configurable options. */
+#define setdefaults do{ \
+	align = -1; \
+	count = 0; \
+	debug = 2; \
+	fmt_output = fmt_asv; \
+	noerror = 0; \
+	ep[0].fl = read_flags; \
+	Io_setdefaults(&ep[0]); \
+	ep[1].fl = write_flags; \
+	Io_setdefaults(&ep[1]); }while(0)
+
 #define MIN(a, b) (((a) < (b)) ? (a) : (b))
-#define MAX(a, b) (((a) > (b)) ? (a) : (b))
 
 /* Macro to check if fd is a std* file, e.g. stdin. */
 #define fdisstd(fd) \
@@ -73,11 +104,38 @@ static int write_flags = O_WRONLY | O_CREAT; /* dd(1). */
  * particular io[2] used in main. Error conditions are not checked because this
  * is only used when the program is about to terminate (hence its name). */
 #define terminate(io) do{ \
-	free((io)[0].buf); \
+	Io_buffree(&(io)[0]); \
-	free((io)[1].buf); \
+	Io_buffree(&(io)[1]); \
 	Io_fdclose(&(io)[0]); \
 	Io_fdclose(&(io)[1]); }while(0)
 
+/* Allocates *io's buffer. Returns NULL if unsuccessful. */
+static void *
+Io_bufalloc(struct Io *io){
+
+	return (io->buf = malloc(io->bs * (sizeof *io->buf)));
+}
+
+/* Frees *io's buffer. Returns io. */
+static struct Io *
+Io_buffree(struct Io *io){
+
+	free(io->buf);
+
+	return io;
+}
+
+/* Fills the unused portion of io's buffer with padding, updating io->bufuse.
+ * Returns io. */
+static struct Io *
+Io_bufrpad(struct Io *io, int padding){
+	
+	memset(io->buf + io->bufuse, padding, io->bs - io->bufuse);
+	io->bufuse = io->bs;
+
+	return io;
+}
+
 /* Copies from the buffer in src as much as possible to the free space in the
  * dest buffer, removing the copied units from src and permuting the remaining
  * units in the src buffer to the start of the buffer, modifying both the src
@@ -109,10 +167,13 @@ Io_bufxfer(struct Io *dest, struct Io *src, int n){
 }
 
 /* Closes io->fn and returns -1 on error, otherwise io->fd. */
-#define Io_fdclose(io) \
+static int
-	(fdisstd((io)->fd) \
+Io_fdclose(struct Io *io){
-		? 0 \
+
-		: close((io)->fd))
+	return fdisstd(io->fd)
+		? 0
+		: close(io->fd);
+}
 
 /* Opens io->fn and saves the file descriptor into io->fd. Returns io->fd,
  * which will be -1 if an error occured. */
@@ -138,6 +199,7 @@ Io_fdopen(struct Io *io, char *fn){
  * be set to zero to indicate the seek occurred. */
 static int
 Io_fdseek(struct Io *io){
+	int (*op)(int, void *, size_t);
 	
 	if(!fdisstd(io->fd) && lseek(io->fd, io->seek, SEEK_SET) != -1)
 		return -1;
@@ -221,6 +283,19 @@ oserr(char *s){
 	return EX_OSERR;
 }
 
+/* Prints statistics regarding the use of dj, particularly partially and
+ * completely read and written records, accessing debug, ep, and fmt_output. */
+static void
+output(void){
+
+	if(debug >= 1)
+		fprintf(stderr, fmt_output,
+			ep[0].rec, ep[0].prec, ep[1].rec, ep[1].prec,
+			ep[0].bytes, ep[1].bytes);
+
+	return;
+}
+
 /* Parses the string s to an integer, returning either the integer or in the
  * case of an error a negative integer. This is used for argument parsing
  * (e.g. -B [int]) in dj and no negative integer would be valid anyway. */
@@ -246,30 +321,11 @@ usage(void){
 	return EX_USAGE;
 }
 
-/* For use in main only.
- * Prints statistics regarding the use of dj, particularly partially and
- * completely read and written records, accessing ep, and fmt_output. */
-#define output fprintf(stderr, fmt_output, \
-	ep[0].rec, ep[0].prec, ep[1].rec, ep[1].prec, ep[0].bytes, ep[1].bytes \
-)
-
 int main(int argc, char *argv[]){
-	int align; /* Only the lower 8b are used, negative if no alignment. */
+	int c;
-	int count;
+	int i;
-	int c, i;
-	enum { QUIETER = 0, TYPICAL = 1, VERBOSE = 2 } debug;
-	enum { GIVEUP = 0, RETRY = 1 } error;
-	char *fmt_output = fmt_asv;
 
-	ep[0].fl = read_flags;
+	setdefaults;
-	Io_setdefaults(&ep[0]);
-	ep[1].fl = write_flags;
-	Io_setdefaults(&ep[1]);
-
-	align = -1;
-	count = 0;
-	debug = TYPICAL;
-	error = GIVEUP;
 
 	if(argc > 0){
 		program_name = argv[0];
@@ -286,10 +342,10 @@ int main(int argc, char *argv[]){
 				terminate(ep);
 				return oserr(optarg);
 			case 'A': align = '\0'; break;
-			case 'd': debug = VERBOSE; break;
+			case 'd': ++debug; break;
-			case 'n': error = RETRY; break;
+			case 'n': noerror = 1; break;
 			case 'H': fmt_output = fmt_human; break;
-			case 'q': debug = QUIETER; break;
+			case 'q': --debug; break;
 			case 'a':
 				if(optarg[0] != '\0' && optarg[1] == '\0'){
 					align = optarg[0];
@@ -311,15 +367,14 @@ int main(int argc, char *argv[]){
 			}
 	}
 
-	if(debug >= VERBOSE)
+	if(debug >= 3)
 		fprintf(stderr,
 			"argv0=%s\n"
 			"in=%s\tibs=%d\tskip=%ld\talign=%hhx\tcount=%d\n"
-			"out=%s\tobs=%d\tseek=%ld\tdebug=%2d\terror=%s\n",
+			"out=%s\tobs=%d\tseek=%ld\tdebug=%2d\tnoerror=%d\n",
 			program_name,
 			ep[0].fn, ep[0].bs, ep[0].seek, align, count,
-			ep[1].fn, ep[1].bs, ep[1].seek, debug,
+			ep[1].fn, ep[1].bs, ep[1].seek, debug, noerror);
-		    error == GIVEUP ? "GIVEUP" : "RETRY");
 
 	if(argc > optind){
 		terminate(ep);
@@ -327,37 +382,36 @@ int main(int argc, char *argv[]){
 	}
 
 	for(i = 0; i <= 1; ++i){
-		if((ep[i].buf = malloc(ep[i].bs * (sizeof ep[i].buf))) == NULL){
+		if(Io_bufalloc(&ep[i]) == NULL){
 			fprintf(stderr, "%s: Failed to allocate %d bytes\n",
-				program_name, ep[i].bs * (sizeof ep[i].buf));
+				program_name, ep[i].bs);
 			terminate(ep);
 			return EX_OSERR;
-		}else if(ep[i].seek > 0 && (c = Io_fdseek(&ep[i])) != -1){
+		}else if(ep[i].seek > 0)
-			output;
+			switch(Io_fdseek(&ep[i])){
+			case EX_OK:
+				output();
 				terminate(ep);
-			return c;
+				return EX_OK;
 			}
 	}
 
 	do{	/* read */
 		Io_read(&ep[0]);
-		if(error == RETRY && ep[0].bufuse == 0)
+		if(!noerror && ep[0].bufuse == 0)
 			Io_read(&ep[0]); /* second chance */
 		if(ep[0].bufuse == 0) /* that's all she wrote */
 			break;
 		else if(ep[0].bufuse < ep[0].bs){
 			++ep[0].prec;
-			if(debug >= TYPICAL){
+			if(debug >= 2){
 				fprintf(stderr, "%s: Partial read:\n\t", program_name);
-				output;
+				output();
 			}
-			if(error == GIVEUP)
+			if(!noerror)
 				count = 1;
-			if(align >= 0){
+			if(align >= 0)
-				memset(ep[0].buf + ep[0].bufuse, align,
+				Io_bufrpad(&ep[0], align);
-					ep[0].bs - ep[0].bufuse);
-				ep[0].bufuse = ep[0].bs;
-			}
 		}else
 			++ep[0].rec;
 
@@ -371,18 +425,18 @@ int main(int argc, char *argv[]){
 
 			c = ep[1].bufuse;
 			Io_write(&ep[1]);
-			if(error == GIVEUP && ep[1].bufuse == c)
+			if(!noerror && ep[1].bufuse == c)
 				Io_write(&ep[1]); /* second chance */
 			if(c == ep[1].bufuse){ /* no more love */
 				count = 1;
 				break;
 			}else if(c > ep[1].bufuse && ep[1].bufuse > 0){
 				ep[1].prec += 1;
-				if(debug >= TYPICAL){
+				if(debug >= 2){
 					fprintf(stderr, "%s: Partial write:\n\t", program_name);
-					output;
+					output();
 				}
-				if(error == GIVEUP)
+				if(!noerror)
 					count = 1;
 			}else if(ep[1].bufuse == 0 && c < ep[1].bs)
 				++ep[1].prec;
@@ -391,7 +445,7 @@ int main(int argc, char *argv[]){
 		}while(ep[0].bufuse > 0);
 	}while(count == 0 || --count > 0);
 
-	output;
+	output();
 	terminate(ep);
 
 	return EX_OK;

src/fop.rs

@@ -22,10 +22,12 @@ use std::{
 	process::{ Command, exit, Stdio },
 };
 
-extern crate sysexits;
 extern crate getopt;
+extern crate strerror;
+extern crate sysexits;
 
 use getopt::{ Opt, Parser };
+use strerror::StrError;
 use sysexits::{ EX_DATAERR, EX_IOERR, EX_UNAVAILABLE, EX_USAGE };
 
 fn main() {
@@ -55,7 +57,7 @@ fn main() {
 	});
 
 	let index = argv[index_arg].parse::<usize>().unwrap_or_else(|e| {
-		eprintln!("{}: {}: {}.", argv[0], argv[1], e);
+		eprintln!("{}: {}: {}", argv[0], argv[1], e);
 		exit(EX_DATAERR);
 	});
 
@@ -75,13 +77,13 @@ fn main() {
 		.stdout(Stdio::piped())
 		.spawn()
 		.unwrap_or_else( |e| {
-			eprintln!("{}: {}: {}.", argv[0], argv[command_arg], e);
+			eprintln!("{}: {}: {}", argv[0], argv[command_arg], e.strerror());
 			exit(EX_UNAVAILABLE);
 		});
 
 	let field = fields.get(index).unwrap_or_else(|| {
 		eprintln!(
-			"{}: {}: No such index in input.",
+			"{}: {}: No such index in input",
 			argv[0],
 			index.to_string(),
 		);
@@ -94,7 +96,7 @@ fn main() {
 	}
 
 	let output = spawned.wait_with_output().unwrap_or_else(|e| {
-		eprintln!("{}: {}: {}.", argv[0], argv[command_arg], e);
+		eprintln!("{}: {}: {}", argv[0], argv[command_arg], e.strerror());
 		exit(EX_IOERR);
 	});
 
@@ -103,7 +105,7 @@ fn main() {
 	if replace.pop() != Some(b'\n') { replace = output.stdout; }
 
 	let new_field = String::from_utf8(replace).unwrap_or_else(|e| {
-		eprintln!("{}: {}: {}.", argv[0], argv[command_arg], e);
+		eprintln!("{}: {}: {}", argv[0], argv[command_arg], e);
 		exit(EX_IOERR);
 	});
 
@@ -112,7 +114,7 @@ fn main() {
 	stdout().write_all(
 		fields.join(&d.to_string()).as_bytes()
 	).unwrap_or_else(|e| {
-		eprintln!("{}: {}.", argv[0], e);
+		eprintln!("{}: {}", argv[0], e.strerror());
 		exit(EX_IOERR);
 	});
 }

src/hru.rs

@@ -23,8 +23,10 @@ use std::{
 	process::{ ExitCode, exit },
 };
 
+extern crate strerror;
 extern crate sysexits;
 
+use strerror::StrError;
 use sysexits::{ EX_DATAERR, EX_IOERR, EX_SOFTWARE };
 
 const LIST: [(u32, &str); 10] = [
@@ -49,7 +51,7 @@ fn convert(input: u128) -> Result<(f64, (u32, &'static str)), String> {
 		let c = match 10_u128.checked_pow(n) {
 			Some(c) => c,
 			None => {
-				return Err(format!("10^{}: Integer overflow.", n.to_string()));
+				return Err(format!("10^{}: Integer overflow", n.to_string()));
 			},
 		};
 
@@ -79,7 +81,7 @@ fn main() -> ExitCode {
 				f
 			},
 			Err(err) => {
-				eprintln!("{}: {}.", argv[0], err);
+				eprintln!("{}: {}", argv[0], err);
 				return ExitCode::from(EX_DATAERR as u8);
 			},
 		};
@@ -87,7 +89,7 @@ fn main() -> ExitCode {
 		let (number, prefix) = match convert(n) {
 			Ok(x) => x,
 			Err(err) => {
-				eprintln!("{}: {}.", argv[0], err);
+				eprintln!("{}: {}", argv[0], err);
 				return ExitCode::from(EX_SOFTWARE as u8);
 			},
 		};
@@ -98,7 +100,7 @@ fn main() -> ExitCode {
 
 		stdout().write_all(format!("{} {}\n", out, si_prefix).as_bytes())
 			.unwrap_or_else(|e| {
-				eprintln!("{}: {}.", argv[0], e);
+				eprintln!("{}: {}", argv[0], e.strerror());
 				exit(EX_IOERR);
 			});
 	}

src/pg.c

@@ -0,0 +1,260 @@
+/*
+ * 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 <errno.h> /* errno */
+#include <stdio.h> /* fclose(3), feof(3), fgetc(3), fgets(3), fopen(3),
+                    * fprintf(3), fputc(3), stderr, stdin, stdout, EOF, FILE,
+                    * NULL */
+#include <stdlib.h> /* size_t */
+#include <string.h> /* strchr(3), strcmp(3), strerror(3), strtok(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 {
+	size_t quantity;
+	enum { LINES = 0, BYTES = 1 } type;
+} default_page_unit = { 22, LINES } /* Plan 9 default */;
+static FILE *input;
+static char *prompt = ": ";
+static char *program_name = "pg";
+
+static char *permute_out(char *str, size_t index){
+	size_t j;
+
+	for(j = index; str[j - 1] != '\0'; ++j)
+		str[j - 1] = str[j];
+
+	return str;
+}
+
+/* strtok(3p), but supports double-quotes and escapes (but only for escaping
+ * quotes). UTF-8 is safe only in str. Unmatched quotes in str are considered
+ * literal. The behavior of strtok_quoted when '"' or '\\' are in sep is
+ * undefined. */
+/* TODO: Seems to only ever return NULL. */
+static char *strtok_quoted(char *str, char *sep){
+	static char *s;
+	size_t i;
+	size_t j;
+
+	if(str != NULL)
+		s = str;
+
+	while(strchr(sep, *s) == NULL)
+		if(*++s == '\0')
+			return NULL; /* no remaining characters except seperators */
+
+	{
+		char in_escape;
+		int in_quotes;
+
+		in_escape = 0;
+		in_quotes = -1;
+		for(i = 0; s[i] != '\0'; ++i)
+			switch(s[i]){
+			case '\\':
+				if(in_escape)
+					permute_out(s, i--);
+				in_escape = !in_escape;
+				break;
+			case '"':
+				if(in_escape){
+					s[i] = s[i - 1];
+					permute_out(s, i--);
+				}else if(in_quotes != -1){
+					permute_out(s, in_quotes);
+					--i;
+					permute_out(s, i--);
+					in_quotes = -1;
+				}else
+					in_quotes = i;
+				break;
+			case '\0':
+				return s;
+			default:
+				if(!in_escape && strchr(sep, s[i]) != NULL){
+					s[i] = '\0';
+					return s;
+				}
+			}
+	}
+
+	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) /* This shouldn't be possible. */
+		return EX_USAGE;
+	if(default_page_unit.type == BYTES)
+		return pg_b_u(input, default_page_unit.quantity) == EOF
+			? EX_UNAVAILABLE
+			: EX_OK;
+	else if(default_page_unit.type == LINES)
+		return pg_l_u(input, 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:
+		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[] = {
+	{ "", cmd_default_page },
+	{ "+", cmd_page_down_lines },
+
+	/* 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){
+	/* Command line word splitting is naive and based on whitespace ONLY; no
+	 * fancy quoting or escaping here. Adding that would (ideally) entail
+	 * replacing strtok(3) with something specific to this task. */
+	static int argc;
+	static char *argv[ARGV_MAX];
+
+	if((argv[(argc = 0)] = strtok(cmdline, whitespace)) == NULL){
+		while(cmdline[0] != '\0')
+			cmdline = &cmdline[1];
+		argv[argc] = cmdline;
+		argv[++argc] = NULL;
+	}else{
+		while((argv[++argc] = strtok(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);
+
+	fprintf(stderr, "%s: %s: not found\n", program_name, argv[0]);
+	return EX_USAGE;
+}
+
+int usage(char *s){
+	fprintf(stderr, "Usage: %s (-p [prompt])\n", s);
+	return EX_USAGE;
+}
+
+int main(int argc, char *argv[]){
+	unsigned char cmd[CMDLINE_MAX];
+	FILE *t;
+
+	input = stdin;
+
+	if(argc < 1)
+		program_name = argv[0];
+	else{
+		int c;
+
+		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){
+		fprintf(stderr, "%s: /dev/tty: %s\n", program_name, strerror(errno));
+		return EX_OSERR;
+	}
+
+	for(;;){
+		fputs(prompt, stderr);
+		fgets((char *)cmd, (sizeof cmd) / (sizeof *cmd), t);
+		if(strchr((char *)cmd, '\n') == NULL){ /* fast-forward stream */
+			int c;
+
+			while((c = fgetc(t)) != '\n')
+				if(c == EOF)
+					break;
+		}
+
+		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 */
+	return EX_SOFTWARE;
+}

src/rpn.rs

@@ -172,7 +172,7 @@ fn eval(
 					};
 				} else {
 					return Err(EvaluationError {
-						message: format!("{}: Unexpected operation.", op),
+						message: format!("{}: Unexpected operation", op),
 						code: EX_DATAERR,
 					})
 				}

src/strerror.rs

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2024 Emma Tebibyte <emma@tebibyte.media>
+ * SPDX-License-Identifier: FSFAP
+ *
+ * Copying and distribution of this file, with or without modification, are
+ * permitted in any medium without royalty provided the copyright notice and
+ * this notice are preserved.  This file is offered as-is, without any warranty.
+ */
+
+use std::ffi::{ c_int, c_char, CStr };
+
+pub trait StrError { fn strerror(&self) -> String; }
+
+impl StrError for std::io::Error {
+	/* wrapper function for use in Rust */
+	fn strerror(&self) -> String {
+		/* Get the raw OS error. If it’s None, what the hell is going on‽ */
+		let errno = self.raw_os_error().unwrap_or(0) as c_int;
+
+		/* Get a CStr from the error message so that it’s referenced and then
+		 * convert it to an owned value. If the string is not valid UTF-8,
+		 * return that error instead. */
+		match unsafe { CStr::from_ptr(strerror(errno)) }.to_str() {
+			Ok(s) => s.to_owned(), // yay!! :D
+			Err(e) => e.to_string(), // awww :(
+		}
+	}
+}
+
+/* binding to strerror(3p) */
+extern "C" { fn strerror(errnum: c_int) -> *mut c_char; }

src/test.rs

@@ -0,0 +1,10 @@
+extern crate strerror;
+
+use strerror::raw_message;
+
+fn main() {
+	stdout.write_all(b"meow\n").unwrap_or_else(|e| {
+		eprintln!("{}", raw_message(e));
+		std::process::exit(1);
+	});
+}