fix unbound variable error

uberspace-backup.sh

@@ -29,8 +29,6 @@ else
   SSH_KEY=~/.ssh/id_rsa
 fi
 
-ARG1="$1"
-
 # Get current date
 DATE=$(date +"%Y-%m-%d_%H-%M")
 LOG="$CURDIR"/backup.log
@@ -54,8 +52,8 @@ while read -r line; do
 
   RHOST=$(echo "$line" | cut -d";" -f1 | trim)
 
-  # Jump to next line if this line's host does not match host of ARG1 (if given)
-  if [[ "${ARG1}" != "" ]] && [[ "${ARG1}" != "${RHOST}" ]]; then
+  # Jump to next line if this line's host does not match host of first argument (if given)
+  if [[ "${1-}" != "" ]] && [[ "${1-}" != "${RHOST}" ]]; then
     continue
   fi
   # Task ssh-checker.sh to check this host