env: Add a handful of test cases.

MFC after:	3 days
Sponsored by:	Klara, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D46996

(cherry picked from commit 334af5e4131b21c658203635bf713d6a59846585)

env: Improve documentation.

* The `env` utility's inability to run a command whose name contains an
  equal sign is a feature, not a bug, so move that paragraph up from the
  BUGS section to the DESCRIPTION section.

* Mention that this can be worked around by prefixing the command name
  with `command`, and add an example of this to the EXAMPLE section.

* Add a test case which verifies that `env` does not run a command with
  an equal sign in its name even if it exists, and also demonstrates the
  workaround.

MFC after:	3 days
Sponsored by:	Klara, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D46997

(cherry picked from commit a0dfb0668b45506de97beb4c7acbe3fd1ba69fc8)

env: Add an option to change the directory.

This mirrors the equivalent option in GNU coreutils env, but does not
add support for long options.

MFC after:	3 days
Relnotes:	yes
Sponsored by:	Klara, Inc.
Reviewed by:	0mp, bcr
Differential Revision:	https://reviews.freebsd.org/D47008

(cherry picked from commit 6f6166e49c78f6460732c02bbbba6fcc218221cf)

env: Check the status of stdout.

MFC after:	3 days
Sponsored by:	Klara, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D47009

(cherry picked from commit c2d93a803acef634bd0eede6673aeea59e90c277)

6 files changed, 222 insertions, 15 deletions

diff --git a/etc/mtree/BSD.tests.dist b/etc/mtree/BSD.tests.dist
index 95328d6d293f..a756236fd534 100644
--- a/etc/mtree/BSD.tests.dist
+++ b/etc/mtree/BSD.tests.dist
@@ -1057,6 +1057,8 @@
         ..
         du
         ..
+        env
+        ..
         factor
         ..
         file2c
diff --git a/usr.bin/env/Makefile b/usr.bin/env/Makefile
index af2e65dd5fc1..d7a34fce92aa 100644
--- a/usr.bin/env/Makefile
+++ b/usr.bin/env/Makefile
@@ -1,4 +1,5 @@
 #	From: @(#)Makefile	8.1 (Berkeley) 6/6/93
+.include <src.opts.mk>
 
 PACKAGE=	runtime
 PROG=	env
@@ -6,4 +7,7 @@ SRCS=	env.c envopts.c
 
 LIBADD=	util
 
+HAS_TESTS=
+SUBDIR.${MK_TESTS}=	tests
+
 .include <bsd.prog.mk>
diff --git a/usr.bin/env/env.1 b/usr.bin/env/env.1
index 8aa78e110505..4badea716143 100644
--- a/usr.bin/env/env.1
+++ b/usr.bin/env/env.1
@@ -30,7 +30,7 @@
 .\" From @(#)printenv.1	8.1 (Berkeley) 6/6/93
 .\" From FreeBSD: src/usr.bin/printenv/printenv.1,v 1.17 2002/11/26 17:33:35 ru Exp
 .\"
-.Dd March 3, 2021
+.Dd October 8, 2024
 .Dt ENV 1
 .Os
 .Sh NAME
@@ -44,6 +44,7 @@
 .Op Ar name Ns = Ns Ar value ...
 .Nm
 .Op Fl iv
+.Op Fl C Ar altwd
 .Op Fl L Ns | Ns Fl U Ar user Ns Op / Ns Ar class
 .Op Fl P Ar altpath
 .Op Fl S Ar string
@@ -81,6 +82,12 @@ The environment inherited
 by
 .Nm
 is ignored completely.
+.\"     -C
+.It Fl C Ar altwd
+Change to the specified alternate working directory before executing
+the specified
+.Ar utility
+program.
 .\"	-L | -U
 .It Fl L | Fl U Ar user Ns Op / Ns Ar class
 Add the environment variable definitions from
@@ -173,6 +180,19 @@ Both
 and
 .Ar utility
 may not be specified together.
+.Pp
+The
+.Nm
+utility does not handle values of
+.Ar utility
+which have an equals sign
+.Pq Ql =
+in their name, for obvious reasons.
+This can easily be worked around by interposing the
+.Xr command 1
+utility, which simply executes its arguments; see
+.Sx EXAMPLES
+below.
 .\"
 .Ss Details of -S (split-string) processing
 The processing of the
@@ -471,6 +491,11 @@ and
 options:
 .Pp
 .Dl "#!/usr/bin/env -S-P/usr/local/bin:/usr/bin:${PATH} perl"
+.Pp
+To execute a utility with an equal sign in its name:
+.Bd -literal -offset indent
+env name=value ... command foo=bar arg ...
+.Ed
 .Sh COMPATIBILITY
 The
 .Nm
@@ -490,7 +515,7 @@ The
 utility conforms to
 .St -p1003.1-2001 .
 The
-.Fl 0 , L , P , S , U , u
+.Fl 0 , C , L , P , S , U , u
 and
 .Fl v
 options are non-standard extensions supported by
@@ -513,15 +538,11 @@ and
 .Fl U
 options were added in
 .Fx 13.0 .
-.Sh BUGS
 The
-.Nm
-utility does not handle values of
-.Ar utility
-which have an equals sign
-.Pq Ql =
-in their name, for obvious reasons.
-.Pp
+.Fl C
+option was added in
+.Fx 14.2 .
+.Sh BUGS
 The
 .Nm
 utility does not take multibyte characters into account when
diff --git a/usr.bin/env/env.c b/usr.bin/env/env.c
index 784caa76063e..724a17d8be4f 100644
--- a/usr.bin/env/env.c
+++ b/usr.bin/env/env.c
@@ -72,7 +72,7 @@ static void usage(void) __dead2;
 int
 main(int argc, char **argv)
 {
-	char *altpath, **ep, *p, **parg, term;
+	char *altpath, *altwd, **ep, *p, **parg, term;
 	char *cleanenv[1];
 	char *login_class, *login_name;
 	struct passwd *pw;
@@ -83,6 +83,7 @@ main(int argc, char **argv)
 	int rtrn;
 
 	altpath = NULL;
+	altwd = NULL;
 	login_class = NULL;
 	login_name = NULL;
 	pw = NULL;
@@ -90,7 +91,7 @@ main(int argc, char **argv)
 	login_as_user = false;
 	want_clear = 0;
 	term = '\n';
-	while ((ch = getopt(argc, argv, "-0iL:P:S:U:u:v")) != -1)
+	while ((ch = getopt(argc, argv, "-0C:iL:P:S:U:u:v")) != -1)
 		switch(ch) {
 		case '-':
 		case 'i':
@@ -99,6 +100,9 @@ main(int argc, char **argv)
 		case '0':
 			term = '\0';
 			break;
+		case 'C':
+			altwd = optarg;
+			break;
 		case 'U':
 			login_as_user = true;
 			/* FALLTHROUGH */
@@ -106,7 +110,7 @@ main(int argc, char **argv)
 			login_name = optarg;
 			break;
 		case 'P':
-			altpath = strdup(optarg);
+			altpath = optarg;
 			break;
 		case 'S':
 			/*
@@ -199,6 +203,9 @@ main(int argc, char **argv)
 	if (*argv) {
 		if (term == '\0')
 			errx(EXIT_CANCELED, "cannot specify command with -0");
+		if (altwd && chdir(altwd) != 0)
+			err(EXIT_CANCELED, "cannot change directory to '%s'",
+			    altwd);
 		if (altpath)
 			search_paths(altpath, argv);
 		if (env_verbosity) {
@@ -212,9 +219,16 @@ main(int argc, char **argv)
 		execvp(*argv, argv);
 		err(errno == ENOENT ? EXIT_ENOENT : EXIT_CANNOT_INVOKE,
 		    "%s", *argv);
+	} else {
+		if (altwd)
+			errx(EXIT_CANCELED, "must specify command with -C");
+		if (altpath)
+			errx(EXIT_CANCELED, "must specify command with -P");
 	}
 	for (ep = environ; *ep; ep++)
 		(void)printf("%s%c", *ep, term);
+	if (fflush(stdout) != 0)
+		err(1, "stdout");
 	exit(0);
 }
 
@@ -222,7 +236,7 @@ static void
 usage(void)
 {
 	(void)fprintf(stderr,
-	    "usage: env [-0iv] [-L|-U user[/class]] [-P utilpath] [-S string] [-u name]\n"
-	    "           [name=value ...] [utility [argument ...]]\n");
+	    "usage: env [-0iv] [-C workdir] [-L|-U user[/class]] [-P utilpath] [-S string]\n"
+	    "           [-u name] [name=value ...] [utility [argument ...]]\n");
 	exit(1);
 }
diff --git a/usr.bin/env/tests/Makefile b/usr.bin/env/tests/Makefile
new file mode 100644
index 000000000000..3d2f77b34b67
--- /dev/null
+++ b/usr.bin/env/tests/Makefile
@@ -0,0 +1,6 @@
+PACKAGE=	tests
+
+ATF_TESTS_SH=	env_test
+BINDIR=		${TESTSDIR}
+
+.include <bsd.test.mk>
diff --git a/usr.bin/env/tests/env_test.sh b/usr.bin/env/tests/env_test.sh
new file mode 100644
index 000000000000..2dc8f1a4c911
--- /dev/null
+++ b/usr.bin/env/tests/env_test.sh
@@ -0,0 +1,160 @@
+#
+# Copyright (c) 2024 Klara, Inc.
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+
+magic_words="Squeamish $$ Ossifrage"
+
+atf_test_case basic
+basic_head()
+{
+	atf_set "descr" "Basic test case"
+}
+basic_body()
+{
+	atf_check -o match:"^magic_words=${magic_words}\$" \
+		  env magic_words="${magic_words}"
+	export MAGIC_WORDS="${magic_words}"
+	atf_check -o match:"^MAGIC_WORDS=${magic_words}\$" \
+		  env
+	unset MAGIC_WORDS
+}
+
+atf_test_case unset
+unset_head()
+{
+	atf_set "descr" "Unset a variable"
+}
+unset_body()
+{
+	export MAGIC_WORDS="${magic_words}"
+	atf_check -o not-match:"^MAGIC_WORDS=" \
+		  env -u MAGIC_WORDS
+	unset MAGIC_WORDS
+}
+
+atf_test_case empty
+empty_head()
+{
+	atf_set "descr" "Empty environment"
+}
+empty_body()
+{
+	atf_check env -i
+}
+
+atf_test_case true
+true_head()
+{
+	atf_set "descr" "Run true"
+}
+true_body()
+{
+	atf_check env true
+}
+
+atf_test_case false
+false_head()
+{
+	atf_set "descr" "Run false"
+}
+false_body()
+{
+	atf_check -s exit:1 env false
+}
+
+atf_test_case false
+false_head()
+{
+	atf_set "descr" "Run false"
+}
+false_body()
+{
+	atf_check -s exit:1 env false
+}
+
+atf_test_case altpath
+altpath_head()
+{
+	atf_set "descr" "Use alternate path"
+}
+altpath_body()
+{
+	echo "echo ${magic_words}" >magic_words
+	chmod 0755 magic_words
+	atf_check -s exit:125 -e match:"must specify command" \
+		  env -P "${PWD}"
+	atf_check -s exit:127 -e match:"No such file" \
+		  env magic_words
+	atf_check -o inline:"${magic_words}\n" \
+		  env -P "${PWD}" magic_words
+}
+
+atf_test_case equal
+equal_head()
+{
+	atf_set "descr" "Command name contains equal sign"
+}
+equal_body()
+{
+	echo "echo ${magic_words}" >"magic=words"
+	chmod 0755 "magic=words"
+	atf_check -o match:"^${PWD}/magic=words$" \
+		  env "${PWD}/magic=words"
+	atf_check -s exit:125 -e match:"must specify command" \
+		  env -P "${PATH}:${PWD}" "magic=words"
+	atf_check -o inline:"${magic_words}\n" \
+		  env command "${PWD}/magic=words"
+	atf_check -o inline:"${magic_words}\n" \
+		  env PATH="${PATH}:${PWD}" command "magic=words"
+}
+
+atf_test_case chdir
+chdir_head()
+{
+	atf_set "descr" "Change working directory"
+}
+chdir_body()
+{
+	local subdir="dir.$$"
+	atf_check -o inline:"${PWD}\n" \
+		  env pwd
+	atf_check -s exit:125 -e match:"must specify command" \
+		  env -C "${subdir}"
+	atf_check -s exit:125 \
+		  -e match:"cannot change directory to '${subdir}':" \
+		  env -C "${subdir}" pwd
+	atf_check mkdir "${subdir}"
+	atf_check -o inline:"${PWD}/${subdir}\n" \
+		  env -C "${subdir}" pwd
+}
+
+atf_test_case stdout
+stdout_head()
+{
+	atf_set descr "Failure to write to stdout"
+}
+stdout_body()
+{
+	(
+		trap "" PIPE
+		env 2>stderr
+		echo $? >result
+	) | true
+	atf_check -o inline:"1\n" cat result
+	atf_check -o match:"stdout" cat stderr
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case basic
+	atf_add_test_case unset
+	atf_add_test_case empty
+	atf_add_test_case true
+	atf_add_test_case false
+	atf_add_test_case altpath
+	atf_add_test_case equal
+	atf_add_test_case chdir
+	atf_add_test_case stdout
+}