Search for nft instead of assuming /usr/bin location

The script now locates the nft program rather than assuming it's
pathname. Also prints the location of the nft program. Thank you to
@jarppiko for finding this issue and submitting a pull request.
Fixes #32

When checking write access of pathnames for the geo_conf and errorlog
files, extract the pathname from the variable instead of assuming it's
location in /etc. Thank you to @electrofloat for finding this issue.
Fixes #30

Make error checking in the check_nftables function more robust.

Remove old commented out code line.

geo-nft.sh

@@ -15,24 +15,25 @@
 # https://github.com/wirefalls/geo-nft
 # https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2
 #
-# This script requires write access to /etc, /var/log and the install
-# directory (base_dir), which by default is: /etc/nftables/geo-nft.
+# This script requires write access to the pathnames of the geo_conf and
+# errorlog files as well as the install directory (base_dir), which by
+# default is: /etc/nftables/geo-nft.
 #
 # Supply the -s command line argument to silence verbose output.
 #======================================================================
 
 # Standard script variables.
 
 # Semantic version number of this script.
-geo_nft_ver=v2.2.9
+geo_nft_ver=v2.2.10
 
 # Filename of this script.
 script_name="geo-nft.sh"
 
-# User configuration file.
+# User configuration pathname/filename.
 geo_conf="/etc/geo-nft.conf"
 
-# Error log filename. This file logs errors in addition to the systemd Journal.
+# Error log pathname/filename. This file logs errors in addition to the systemd Journal.
 errorlog="/var/log/geo-nft-error.log"
 
 # Geolocation database filename.
@@ -100,14 +101,23 @@ error_log() {
 	fi
 }
 
+# Verify that the nft program is available and store it's pathname.
+nft="$(command -v nft)"
+if [ ! $? -eq 0 ]; then
+	error_log "Unable to find the 'nft' program to determine it's pathname. Verify that" \
+			"the nft program is located in a directory in your PATH environment" \
+			"variable. The nft program is part of the 'nftables' package. Exiting..."
+	exit 1
+fi
+
 # Verify the status of nftables
 check_nftables() {
 	nftables_status="$(systemctl is-active nftables.service)"
-	if [ "$nftables_status" = "inactive" ]; then
+	if [ "$nftables_status" != "active" ]; then
 		print_line "\n"
-		error_log "Nftables is not active. Verify that nftables is installed" \
+		error_log "nftables is not active. Verify that nftables is installed" \
 			"and running with: sudo systemctl status nftables" \
-			"Nftables can be restarted with: sudo systemctl restart nftables"
+			"nftables can be restarted with: sudo systemctl restart nftables"
 	fi
 }
 
@@ -361,16 +371,13 @@ check_dir() {
 
 # Verify that required programs are available.
 check_programs() {
-	local reqd_programs="awk curl grep gunzip nft sed sort stat"
+	local reqd_programs="awk curl grep gunzip sed sort stat"
 
 	for p in $reqd_programs
 	do
 		command -v "$p" > /dev/null 2>&1
 		if [ ! $? -eq 0 ]; then
 			error_log "This script requires the '$p' program, not found in \$PATH. Exiting..."
-			if [ "$p" = "nft" ]; then
-				error_log "The 'nft' program is part of the 'nftables' package."
-			fi
 			exit 1
 		fi
 	done
@@ -441,7 +448,7 @@ check_refill_config() {
 		print_line "\n" "Checking for settings in $refill_conf" "\n"
 
 		# Create an array to store the output that will be written to the refill-sets.nft script.
-		local refill_sets_array=("#!/usr/bin/nft -f")
+		local refill_sets_array=("#!${nft} -f")
 		refill_sets_array+=("")
 		refill_sets_array+=("#=====================================================")
 		refill_sets_array+=("# Auto-generated by $script_name $geo_nft_ver - Do not modify")
@@ -563,7 +570,6 @@ check_refill_config() {
 
 							# Test if the country code is already in the array (country code repeated in refill-sets.conf list).
 							if [[ "${cc4_array[*]}" =~ (^|[^[:alpha:]])$cc([^[:alpha:]]|$) ]]; then
-							#if [[ -v $cc4_array[$cc] ]]; then
 								error_log "Country code '$cc' is duplicated in your 'define-ipv4' line in $refill_conf." \
 									"Remove any duplicates from the line shown below. The duplicate entry will be skipped." \
 									"Bad line: $line"
@@ -1052,8 +1058,11 @@ main() {
 	# Start a timer for the script run time.
 	local starttime=$(date +%s)
 
-	# Verify that the /etc directory is writable.
-	check_dir "/etc"
+	# Verify that the $geo_conf directory exists and is writable.
+	check_dir "${geo_conf%/*}"
+
+	# Verify that the $errorlog directory exists and is writable.
+	check_dir "${errorlog%/*}"
 
 	# Verify that required programs are available.
 	check_programs
@@ -1073,6 +1082,9 @@ main() {
 	# Print the nftables version string from the nft program.
 	print_line "\n" "$(nft -v)" "\n"
 
+	# Print the location of the nft program.
+	print_line "\n" "Found 'nft' in: ${nft%/*}" "\n"
+
 	# Set user default settings.
 	set_defaults