run(1) works

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 run scrut str strcmp swab true
 
 # keep build/include until bindgen(1) has stdin support
 # https://github.com/rust-lang/rust-bindgen/issues/2703
@@ -127,6 +127,11 @@ rpn: build/bin/rpn
 build/bin/rpn: src/rpn.rs build rustlibs
 	$(RUSTC) $(RUSTFLAGS) $(RUSTLIBS) -o $@ src/rpn.rs
 
+.PHONY: run
+run: build/bin/run
+build/bin/run: src/run.rs build
+	$(RUSTC) $(RUSTFLAGS) $(RUSTLIBS) -o $@ src/run.rs
+
 .PHONY: scrut
 scrut: build/bin/scrut
 build/bin/scrut: src/scrut.c build

docs/simexec.1

@@ -0,0 +1,79 @@
+.\" Copyright (c) 2022–2024 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 SIMEXEC 1 2024-07-23 "Harakit-overgrown X.X.X"
+.SH NAME
+simexec \(en execute a program with argv
+.\"
+.SH SYNOPSIS
+
+simexec
+.B binary argv...
+.SH DESCRIPTION
+Execute a binary with a certain argv.
+.SH CAVEATS
+
+Non-binary programs cannot be executed on their own. The PATH environment
+variable is not used and a valid pathname (relative or absolute) must be
+specified.
+
+.BR simexec (1)
+requires caution.
+.B argv
+are not just the operands for the binary but in fact the direct
+.B argv
+it will receive in runtime;
+the first argv entry is the program\(cqs name, and omitting this, though valid
+use of
+.BR simexec (1),
+can break false assumptions made by programmers.
+for example, the
+.BR true (1)
+implementation in the GNU coreutils project suffers a segmentation fault it is
+given no argv[0].
+
+While POSIX.1-2017 doesn't mandate there being an argv[0] per se, a Strictly
+Conforming POSIX Application must pass an argv[0]. It has also been said that
+those who do not pass an argv[0] are mean and nasty and smell of elderberries.
+
+.BR simexec (1)
+directly uses the
+.BR execv (3p)
+library function. It cannot execute shell scripts intelligently (via shebang).
+It is inadviseable to use
+.BR simexec (1)
+to simply execute a program when other methods would suffice.
+.\"
+.SH DIAGNOSTICS
+
+.BR simexec (1)
+exits with the returned value of
+.BR execv (3p),
+which will be 255 if an error occurs in execution, such as the binary not being
+found.
+This is indistinguishable from the executed binary exiting with the same
+status.
+
+Simexec will print a error message and return the proper
+.BR sysexits.h (3)
+value if invoked in an invalid manner.
+.\"
+.SH AUTHOR
+
+Written by DTB
+.MT trinity@trinity.moe
+.ME .
+.\"
+.SH COPYRIGHT
+.\"
+Copyright \(co 2022–2024 DTB. License AGPLv3+: GNU AGPL version 3 or later
+<https://gnu.org/licenses/gpl.html>.
+.\"
+.SH SEE ALSO
+.BR execv (3p)
+
+The C89 standard's draft, section 2.1.2.2: "Hosted environment".
+
+POSIX.1-2017 System Interfaces: execv. Particularly under the RATIONALE section header.

src/run.rs

@@ -0,0 +1,99 @@
+/*
+ * Copyright (c) 2022–2024 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/.
+ */
+
+use std::{
+	env::args,
+	io::Error,
+	os::unix::process::CommandExt,
+	process::{ Command, ExitCode }
+};
+
+extern crate getopt;
+use getopt::GetOpt;
+
+extern crate strerror;
+use strerror::StrError;
+
+extern crate sysexits;
+use sysexits::{ EX_UNAVAILABLE, EX_USAGE };
+
+fn error(p: &str, n: &str, e: Error) -> ExitCode {
+	eprintln!("{}: {}: {}", p, n, e.strerror());
+	ExitCode::from(EX_UNAVAILABLE as u8)
+}
+
+fn usage(s: &str) -> ExitCode {
+	eprintln!("Usage: {} command [argument...]", s);
+	ExitCode::from(EX_USAGE as u8)
+}
+
+fn main() -> ExitCode {
+	let argv = args().collect::<Vec<String>>();
+	let mut optind = 1;
+
+	/* arg0 is None if no argv[0] is meant to be given (argc will be 0),
+	 * however I don't know how to do this in Rust, so the option is currently
+	 * meaningless. -z will set this to None. */
+	let mut arg0: Option<String> = Some(String::default());
+	let mut dir = String::from("."); // $PWD for command
+
+	while let Some(opt) = argv.getopt("C:n:z") {
+		match opt.opt() {
+			// Consistent with precedent; git, make, tar, etc.
+			Ok("C") => dir = opt.arg().unwrap(),
+			Ok("n") => arg0 = Some(opt.arg().unwrap()),
+			// Ok("z") => arg0 = None,
+			_ => { return usage(&argv[0]); }
+		}
+		optind = opt.ind();
+	}
+
+	if argv.len() - optind < 1 { return usage(&argv[0]); }
+
+	let mut cmd = Command::new(argv[optind].clone());
+	cmd.current_dir(dir.clone());
+
+	match arg0 {
+		Some(a) if a != String::default() => { cmd.arg0(a); },
+		_ => () // TODO: argv[0]==NULL support
+	}
+
+	if argv.len() - optind > 1 { // there are arguments
+		let cmdargs = argv
+			.iter()
+			.clone()
+			.skip(optind + 1)
+			.collect::<Vec<&String>>();
+		cmd.args(cmdargs);
+	}
+
+	match cmd.spawn() {
+		Ok(mut child) => match child.wait() {
+			Ok(status) => match status.code() {
+				Some(code) => ExitCode::from(code as u8),
+				None => {
+					eprintln!("{}: {}: process terminated by signal",
+						argv[0], argv[2]);
+					ExitCode::FAILURE
+				}
+			},
+			Err(e) => error(&argv[0], &argv[optind], e)
+		},
+		Err(e) => error(&argv[0], &argv[optind], e)
+	}
+}