Fixing github tests on macos.

Added pure shell function to get relative path between two dirs.

Makefile

@@ -1,7 +1,6 @@
 SHELL := bash
 INSTALL ?= install
-UNAME := $(shell uname);
-REALPATH := $(shell if [ "$(UNAME)" == "Darwin" ]; then echo grealpath; else echo realpath; fi)
+UNAME := $(shell uname)
 
 # Make sure we have git:
 ifeq ($(shell which git),)
@@ -24,7 +23,7 @@ INSTALL_BIN  ?= $(PREFIX)/bin
 INSTALL_LIB  ?= $(PREFIX)/share/$(NAME)
 INSTALL_EXT  ?= $(INSTALL_LIB)/$(NAME).d
 INSTALL_MAN1 ?= $(PREFIX)/share/man/man1
-LINK_REL_DIR := $(shell $(REALPATH) --relative-to=$(INSTALL_BIN) $(INSTALL_LIB))
+LINK_REL_DIR := $(shell bash share/pnrelpath.sh $(INSTALL_BIN) $(INSTALL_LIB))
 
 # Docker variables:
 DOCKER_TAG ?= 0.0.6

share/pnrelpath.sh

@@ -0,0 +1,25 @@
+#!/bin/bash
+#
+# from: https://unix.stackexchange.com/questions/573047/how-to-get-the-relative-path-between-two-directories
+#
+# Expects two parameters, source-dir and target-dir, both absolute canonicalized
+# non-empty pathnames, either may be /-ended, neither need exist.
+# Returns result in shell variable $REPLY as a relative path from source-dir
+# to target-dir without trailing /, . if void.
+#
+# Algorithm is from a 2005 comp.unix.shell posting which has now ascended to
+# archive.org.
+
+pnrelpath() {
+    set -- "${1%/}/" "${2%/}/" ''               ## '/'-end to avoid mismatch
+    while [ "$1" ] && [ "$2" = "${2#"$1"}" ]    ## reduce $1 to shared path
+    do  set -- "${1%/?*/}/"  "$2" "../$3"       ## source/.. target ../relpath
+    done
+    REPLY="${3}${2#"$1"}"                       ## build result
+    # unless root chomp trailing '/', replace '' with '.'
+    [ "${REPLY#/}" ] && REPLY="${REPLY%/}" || REPLY="${REPLY:-.}"
+}
+
+pnrelpath "$1" "$2"
+
+echo $REPLY