From b5cd33bfe6e88575d0cbac27d737156d3c3fa4cd Mon Sep 17 00:00:00 2001
From: DTB <trinity@trinity.moe>
Date: Tue, 23 Jul 2024 18:14:24 -0600
Subject: [PATCH] simexec(1): import from trinity/src

---
 docs/simexec.1 | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 src/simexec.c  | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 84 insertions(+)
 create mode 100644 docs/simexec.1
 create mode 100644 src/simexec.c

diff --git a/docs/simexec.1 b/docs/simexec.1
new file mode 100644
index 0000000..5d79338
--- /dev/null
+++ b/docs/simexec.1
@@ -0,0 +1,49 @@
+.TH SIMEXEC 1
+
+.SH NAME
+
+simexec \(en execute a program with the given argv
+
+.SH SYNOPSIS
+
+simexec
+.RB [ pathname ]
+.RB [ argv... ]
+
+.SH DESCRIPTION
+
+Simexec executes a given program with the given argv.
+
+.SH PITFALLS
+
+Non-binary programs cannot be executed. The PATH environment variable is not used and a valid pathname (relative or absolute) must be specified.
+.PP
+Simexec relies on the user to take proper precautions.
+argv is not just the operands for the program but in fact directly the argv it will receive in runtime;
+the first argv entry is the program's name, and forgoing this, though acceptable by simexec, can break customary assumptions.
+for example, the true(1) implementation in the GNU coreutils suffers a segmentation fault if there is no argv[0].
+.PP
+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.
+.PP
+Simexec directly uses the execv library function. It cannot execute shell scripts intelligently (via shebang).
+It is inadviseable to use simexec as an alternative to simply calling a program, and in fact probably inadviseable to use simexec at all.
+
+.SH DIAGNOSTICS
+
+Simexec returns the value of execv(3), which will be -1 (or 0xFF; 255) if an error occurs.
+This is not distinguishable from the executed program returning the same exit status.
+.PP
+Simexec will print a error message and return the proper sysexits(3) value if used in an invalid manner.
+
+.SH COPYRIGHT
+
+Public domain.
+
+.SH SEE ALSO
+
+exec(3)
+.PP
+The C89 standard's draft, section 2.1.2.2: "Hosted environment".
+.PP
+POSIX.1-2017 System Interfaces: execv. Particularly under the RATIONALE section header.
diff --git a/src/simexec.c b/src/simexec.c
new file mode 100644
index 0000000..54f087b
--- /dev/null
+++ b/src/simexec.c
@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2023 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]);
+}