Merge branch 'simexec' into overgrown

Makefile

@@ -32,7 +32,8 @@ RUSTLIBS = --extern getopt=build/o/libgetopt.rlib \
 CFLAGS += -I$(SYSEXITS)
 
 .PHONY: all
-all: dj false fop hru intcmp mm npc pschdir retval rpn scrut str strcmp swab true
+all: dj false fop hru intcmp mm npc pschdir retval rpn scrut simexec str \
+	strcmp swab true
 
 # keep build/include until bindgen(1) has stdin support
 # https://github.com/rust-lang/rust-bindgen/issues/2703
@@ -142,6 +143,11 @@ scrut: build/bin/scrut
 build/bin/scrut: src/scrut.c build
 	$(CC) $(CFLAGS) -o $@ src/scrut.c
 
+.PHONY: simexec
+simexec: build/bin/simexec
+build/bin/simexec: src/simexec.c build
+	$(CC) $(CFLAGS) -o $@ src/simexec.c
+
 .PHONY: str
 str: build/bin/str
 build/bin/str: src/str.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/simexec.c

@@ -0,0 +1,34 @@
+/*
+ * 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/.
+ */
+
+#include <stdio.h> /* fprintf(3), NULL */
+#include <unistd.h> /* execv(3), */
+#include <sysexits.h> /* EX_USAGE */
+
+char *program_name = "simexec";
+
+int main(int argc, char *argv[]){
+	if (argc < 2) {
+		fprintf(stderr, "Usage: %s binary argv...\n",
+			argv[0] == NULL ? program_name : argv[0]
+		);
+		return EX_USAGE;
+	}
+
+	execv(argv[1], &argv[2]);
+}