base: preserve sysupdates channel on initial setup

the first run of update.sh sets up a cron job to run itself
periodically. the update script takes one position argument, the git
branch to pull changes from, which is also known as "sysupdates channel"
- master for stable, dev for testing.

the sysupdates channel was lost in the cron job setup, always defaulting
to master (stable). this commit preserves the original arg value given
to update.sh during the initial run.

base/voidlinux.sh

@@ -1,4 +1,8 @@
 #!/bin/sh
+# base OS tweaks.
+# the script assumes SYSUPDATES_CHANNEL env var is set to the desired changes
+# channel, whatever the update.sh accept which is typically "dev" or "master".
+
 # try to ensure sysupdates are running regularily before doing anoything else
 xbps-install -y snooze
 ln -sfT /etc/sv/snooze-hourly /var/service/snooze-hourly
@@ -11,7 +15,7 @@ if [ ! -f /etc/cron.hourly/sysupdate ]; then
         # run updates approx. every hour
         cat <<EOF > /etc/cron.hourly/sysupdate
 #!/bin/sh
-exec /ssd/sysupdates/update.sh
+exec /ssd/sysupdates/update.sh "$SYSUPDATES_CHANNEL"
 EOF
         chmod +x /etc/cron.hourly/sysupdate
     fi

update.sh

@@ -9,6 +9,7 @@
 # after user confirmation.
 
 # git branch to pull from. defaults to master.
+# another value is "dev", for a development aka unstable version.
 BRANCH="${1:-master}"
 # output everything to a temp file and print its contents only in case of an error,
 # so that when run via a cronjob, the output is empty on success which prevents
@@ -45,6 +46,7 @@ if [ $? -ne 0 ]; then
 fi
 
 # run repo's update script
+export SYSUPDATES_CHANNEL="$BRANCH"
 ./apply.sh >> $LOGFILE 2>&1
 if [ $? -ne 0 ]; then
     echo "ERROR: apply failed"