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

usr.bin/env/env.1

@@ -28,7 +28,7 @@
 .\" SUCH DAMAGE.
 .\" 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 7, 2024
 .Dt ENV 1
 .Os
 .Sh NAME
@@ -171,6 +171,19 @@ 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
@@ -469,6 +482,11 @@ 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
@@ -514,14 +532,6 @@ options were added in
 .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
-The
-.Nm
 utility does not take multibyte characters into account when
 processing the
 .Fl S

usr.bin/env/tests/env_test.sh

@@ -89,6 +89,25 @@ altpath_body()
 		  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 -o match:"^magic=words$" \
+		  env -P "${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_init_test_cases()
 {
 	atf_add_test_case basic
@@ -97,4 +116,5 @@ atf_init_test_cases()
 	atf_add_test_case true
 	atf_add_test_case false
 	atf_add_test_case altpath
+	atf_add_test_case equal
 }