@@ 43,7 43,7 @@ T       diff
 T       du
 T       echo
 T       ed*
-T       env
+  D     env
     W   ex
 T       expand
 T       expr

@@ 37,6 37,8 @@ shell environment. These tools are used for tasks such as:
 :  Compare two sorted files
 |  *dirname*(1)
 :  Print the directory part of a pathname
+|  *env*(1)
+:  Run command with a specified environment
 |  *false*(1)
 :  Exit with status code 1
 |  *head*(1)

@@ 0,0 1,44 @@
+env(1) "ctools"
+
+# NAME
+
+env - set the environment to run a program
+
+# SYNOPSIS
+
+*env* [-i] [_name_=_value_]... [_utility_ [_argument_...]]
+
+# DESCRIPTION
+
+*env* will update the environment based on its arguments, then invoke
+_utility_, passing _arguments_ to it.
+
+If _utility_ is not provided, the resulting environment is written to standard
+output with one _name_=_value_ pair per line.
+
+# OPTIONS
+
+*-i*
+	Clear the inherited environment before setting new variables and invoking
+	_utility_.
+
+# UNSPECIFIED BEHAVIOR
+
+The POSIX standard does not unambiguously specify the behavior of this command
+under certain conditions. Under such conditions, the ctools implementation of
+*env* behaves as follows:
+
+- If the first argument is *'-'*, *env* will exit with an error.
+
+# NOTES
+
+The ctools implementation of *env* uses _execvp_ to execute _utility_. Should
+PATH be unset, _execvp_ may search some default path set by the system and/or
+C library.
+
+# DISCLAIMER
+
+This command is part of ctools and is compatible with POSIX-1.2017, and may
+optionally support XSI extensions. This man page is not intended to be a
+complete reference, and where it disagrees with the specification, the
+specification takes precedence.

@@ 13,6 13,7 @@ man_files = [
 	'cmp.1',
 	'comm.1',
 	'dirname.1',
+	'env.1',
 	'false.1',
 	'head.1',
 	'link.1',

@@ 20,6 20,7 @@ oneshots = [
 	'cmp',
 	'comm',
 	'dirname',
+	'env',
 	'false',
 	'head',
 	'logname',

@@ 0,0 1,78 @@
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+extern char **environ;
+
+static void
+usage(void)
+{
+	fputs("env [-i] [name=value]... [utility [argument...]]\n", stderr);
+}
+
+int
+main(int argc, char *argv[])
+{
+	if (argc > 1 && strcmp(argv[1], "-") == 0) {
+		usage();
+		return 1;
+	}
+
+	char opt;
+	bool clear = false;
+	while ((opt = getopt(argc, argv, "i")) != -1) {
+		switch (opt) {
+		case 'i':
+			clear = true;
+			break;
+		default:
+			usage();
+			return 1;
+		}
+	}
+
+	if (clear) {
+		environ = NULL;
+	}
+
+	argc = argc - optind;
+	argv = &argv[optind];
+
+	int cmd_idx = 0;
+	for (; cmd_idx < argc; cmd_idx++) {
+		if (!strchr(argv[cmd_idx], '=')) {
+			break;
+		}
+	}
+
+	for (int i = 0; i < cmd_idx; i++) {
+		if (putenv(argv[i]) != 0) {
+			perror("env");
+			return 1;
+		}
+	}
+
+	/* No command, print the env */
+	if (cmd_idx == argc) {
+		for (int i = 0; environ[i]; i++) {
+			puts(environ[i]);
+		}
+		return 0;
+	}
+
+	argv = &argv[cmd_idx];
+
+	execvp(argv[0], argv);
+
+	/* if exec returns, it's errored */
+	fprintf(stderr, "env: '%s': %s\n", argv[0], strerror(errno));
+	switch (errno) {
+	case ENOENT:
+		return 127;
+	default:
+		return 126;
+	}
+}

@@ 0,0 1,58 @@
+#!/bin/sh
+tool=env
+. "$HARNESS"
+
+export FOO=bar
+export BAZ=quux
+
+echo ls > "$TMPDIR"/test-script
+
+should_clear_env() (
+	ev="$(env -i)"
+	[ -z "$ev" ]
+)
+
+should_print_env() (
+	ev="$(env | grep '^FOO')"
+	[ "$ev" = "FOO=bar" ]
+	ev="$(env | grep '^BAZ')"
+	[ "$ev" = "BAZ=quux" ]
+)
+
+should_invoke_cmd() (
+	ev="$(env basename a/b/c.d)"
+	[ "$ev" = "c.d" ]
+)
+
+should_invoke_cmd_clean_env() (
+	ev=$(env -i BAR=foo env)
+	[ "$ev" = "BAR=foo" ]
+)
+
+should_invoke_cmd_with_options() (
+	ev=$(largefile | env -i PATH="$PATH" head -n 15)
+	largefile_head=$(largefile | head -n 15)
+	[ "$ev" = "$largefile_head" ]
+)
+
+should_fail_127() (
+	ev="$(env program-does-not-exist 2> /dev/null)"
+	[ $? = 127 ] && [ -z "$ev" ]
+)
+
+should_fail_126() (
+	ev="$(env "$TMPDIR"/test-script 2> /dev/null)"
+	[ $? = 126 ] && [ -z "$ev" ]
+)
+
+should_handle_ddash env cat /dev/null
+
+runtests \
+	should_handle_ddash \
+	should_clear_env \
+	should_print_env \
+	should_invoke_cmd \
+	should_invoke_cmd_clean_env \
+	should_invoke_cmd_with_options \
+	should_fail_127 \
+	should_fail_126

@@ 10,6 10,7 @@ test_files = [
 	'cmp',
 	'comm',
 	'dirname',
+	'env',
 	'false',
 	'head',
 	'logname',