https://github.com/kholtman/afio/pull/16
--- Makefile.orig
+++ Makefile
@@ -83,6 +83,7 @@ CC=gcc
 CFLAGS += $(CFLAGS1) $1 $2 $3 $4 $5 $6 $7 $8 $9 $a $b $c $d $e $(e2) $f $g $I
 LDFLAGS +=
 CPPFLAGS +=
+PREFIX = /usr/local

 afio : afio.o compfile.o exten.o match.o $M
 	$(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) \
@@ -95,8 +96,8 @@ clean:
 	cd regtest; /bin/sh regtest.clean

 install: afio
-	cp afio /usr/local/bin
-	cp afio.1 /usr/share/man/man1
+	cp afio $(DESTDIR)$(PREFIX)/bin
+	cp afio.1 $(DESTDIR)$(PREFIX)/share/man/man1

 # generate default list of -E extensions from manpage
 # note: on sun, I had to change awk command below to nawk or gawk