Index: usr.bin/gzip/tests/Makefile
===================================================================
--- usr.bin/gzip/tests/Makefile
+++ usr.bin/gzip/tests/Makefile
@@ -2,8 +2,13 @@
 
 .include <bsd.own.mk>
 
+PACKAGE=	tests
+
+ATF_TESTS_SH=	zdiff_test
 NETBSD_ATF_TESTS_SH=	gzip_test
 
+${PACKAGE}FILES+=	foo.diff
+
 .include <netbsd-tests.test.mk>
 
 .include <bsd.test.mk>
Index: usr.bin/gzip/tests/foo.diff
===================================================================
--- /dev/null
+++ usr.bin/gzip/tests/foo.diff
@@ -0,0 +1,2 @@
+1a2
+> bar
Index: usr.bin/gzip/tests/zdiff_test.sh
===================================================================
--- /dev/null
+++ usr.bin/gzip/tests/zdiff_test.sh
@@ -0,0 +1,125 @@
+#
+# SPDX-License-Identifier: BSD-2-Clause-FreeBSD
+#
+# Copyright (c) 2022 Kyle Evans <kevans@FreeBSD.org>
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+#
+
+specials="foo'bar foo\"bar foo\$bar"
+
+prepare_files()
+{
+	compressfunc="$1"
+	compresssuffix="$2"
+
+	echo "foo" > foo
+
+	for f in $specials foo; do
+		[ "$f" == "foo" ] || cp foo "$f"
+		atf_check "$compressfunc" -k "$f"
+		atf_check tar -ckf "$f.tar" "$f"
+		atf_check -o save:"$f.$compresssuffix" \
+		    "$compressfunc" -c "$f.tar"
+
+		# Regenerate $f.tar to create a diff from the .$compresssuffix
+		# file, too.
+		echo "bar" >> "$f"
+		atf_check tar -ckf "$f.tar" "$f"
+	done
+}
+
+atf_test_case gzip
+gzip_body()
+{
+	prepare_files gzip tgz
+	cp foo.gz foo.Z
+
+	for f in foo $specials; do
+		atf_check -s exit:1 -o file:"$(atf_get_srcdir)"/foo.diff \
+		    zdiff "$f.gz"
+	done
+
+	atf_check -s exit:1 -o file:"$(atf_get_srcdir)"/foo.diff zdiff foo.Z
+
+	for f in foo $specials; do
+		rm "$f"
+		atf_check -s exit:1 -o match:"Binary files" zdiff "$f.tgz"
+	done
+}
+
+atf_test_case bzip
+bzip_body()
+{
+	prepare_files bzip2 tbz2
+	cp foo.bz2 foo.bz
+
+	for f in foo $specials; do
+		atf_check -s exit:1 -o file:"$(atf_get_srcdir)"/foo.diff \
+		    zdiff "$f.bz2"
+	done
+
+	atf_check -s exit:1 -o file:"$(atf_get_srcdir)"/foo.diff zdiff foo.bz
+
+	for f in foo $specials; do
+		rm "$f"
+		atf_check -s exit:1 -o match:"Binary files" zdiff "$f.tbz2"
+	done
+}
+
+atf_test_case xzip
+xzip_body()
+{
+	prepare_files xz txz
+	cp foo.xz foo.lzma
+
+	for f in foo $specials; do
+		atf_check -s exit:1 -o file:"$(atf_get_srcdir)"/foo.diff \
+		    zdiff "$f.xz"
+	done
+
+	atf_check -s exit:1 -o file:"$(atf_get_srcdir)"/foo.diff zdiff foo.lzma
+
+	for f in foo $specials; do
+		rm "$f"
+		atf_check -s exit:1 -o match:"Binary files" zdiff "$f.txz"
+	done
+}
+
+atf_test_case unknown
+unknown_body()
+{
+	prepare_files xz fxz
+
+	for f in foo $specials; do
+		atf_check -s exit:1 -e match:"unknown suffix$" zdiff "$f.fxz"
+	done
+}
+
+atf_init_test_cases()
+{
+
+	atf_add_test_case gzip
+	atf_add_test_case bzip
+	atf_add_test_case xzip
+	atf_add_test_case unknown
+}
Index: usr.bin/gzip/zdiff
===================================================================
--- usr.bin/gzip/zdiff
+++ usr.bin/gzip/zdiff
@@ -38,48 +38,48 @@
 check_suffix() {
 	case "$1" in
 	*[._-][Zz])
-		setvar $2 "${1%??}"
-		setvar $3 "gzip -cdqf"
+		eval "$2=\${1%??}"
+		eval "$3=\"gzip -cdqf\""
 		;;
 	*[._-]bz)
-		setvar $2 "${1%???}"
-		setvar $3 "bzip2 -cdqf"
+		eval "$2=\${1%???}"
+		eval "$3=\"bzip2 -cdqf\""
 		;;
 	*[._-]gz)
-		setvar $2 "${1%???}"
-		setvar $3 "gzip -cdqf"
+		eval "$2=\${1%???}"
+		eval "$3=\"gzip -cdqf\""
 		;;
 	*[._-]xz)
-		setvar $2 "${1%???}"
-		setvar $3 "xz -cdqf"
+		eval "$2=\${1%???}"
+		eval "$3=\"xz -cdqf\""
 		;;
 	*[._-]bz2)
-		setvar $2 "${1%????}"
-		setvar $3 "bzip2 -cdqf"
+		eval "$2=\${1%????}"
+		eval "$3=\"bzip2 -cdqf\""
 		;;
 	*[._-]lzma)
-		setvar $2 "${1%?????}"
-		setvar $3 "xz -cdqf"
+		eval "$2=\${1%?????}"
+		eval "$3=\"xz -cdqf\""
 		;;
 	*.t[ag]z)
-		setvar $2 "${1%??}"ar
-		setvar $3 "gzip -cdqf"
+		eval "$2=\${1%??}ar"
+		eval "$3=\"gzip -cdqf\""
 		;;
 	*.tbz)
-		setvar $2 "${1%??}"ar
-		setvar $3 "bzip2 -cdqf"
+		eval "$2=\${1%??}ar"
+		eval "$3=\"bzip2 -cdqf\""
 		;;
 	*.tbz2)
-		setvar $2 "${1%???}"ar
-		setvar $3 "bzip2 -cdqf"
+		eval "$2=\${1%???}ar"
+		eval "$3=\"bzip2 -cdqf\""
 		;;
 	*.t[lx]z)
-		setvar $2 "${1%??}"ar
-		setvar $3 "xz -cdqf"
+		eval "$2=\${1%??}ar"
+		eval "$3=\"xz -cdqf\""
 		;;
 	*)
-		setvar $2 "$1"
-		setvar $3 ""
+		eval "$2=\$1"
+		eval "$3=\"\""
 		;;
 	esac
 }