Be more strict when validating YES/NO configuration variables.

This way users won't be surprised when misspelling "no" as "np" and
getting a "yes" behavior...

Signed-off-by: Mauro Giachero <mauro.giachero@gmail.com>

ChangeLog-current.txt

@@ -20,4 +20,5 @@ enhancements:
   * Add the ability to run multiple sbopkg instances simultaneously. This has
     been suggested many times in the past. Users should read the sbopkg.conf
     man page before using this option (which is disabled by default).
+  * Be more strict validating YES/NO configuration variables.
 +--------------------------+

src/usr/sbin/sbopkg

@@ -135,15 +135,9 @@ EOF
     fi
 
     # Convert some YES/NO variables into 'set/unset' ones.
-    if [[ $KEEPLOG == [Nn][Oo] ]]; then
-        unset KEEPLOG
-    fi
-    if [[ $CLEANUP == [Nn][Oo] ]]; then
-        unset CLEANUP
-    fi
-    if [[ $ALLOW_MULTI == [Nn][Oo] ]]; then
-        unset ALLOW_MULTI
-    fi
+    yesno_to_setunset KEEPLOG
+    yesno_to_setunset CLEANUP
+    yesno_to_setunset ALLOW_MULTI
 
     # If multiple instances of sbopkg are allowed, they need their own
     # private $SBOPKGTMP.
@@ -190,6 +184,35 @@ EOF
     [[ -x /usr/bin/tput ]] && HAS_NCURSES=1
 }
 
+yesno_to_setunset() {
+    # Convert a yes/no variable to a set/unset one.
+    # $1 = variable name
+    # If the variable value is different from "yes" and "no" (case
+    # insensitive) spit an error message and exit.
+
+    # Note: $(eval echo \$$1) is the value of the variable (remember that
+    # $1 is the variable _name_).
+
+    if [[ $(eval echo \$$1) == [Nn][Oo] ]]; then
+        unset $1
+    elif [[ $(eval echo \$$1) != [Yy][Ee][Ss] ]]; then
+        cat <<EOF
+
+ERROR
+$SCRIPT: Unexpected value in $1
+
+The configuration variable $1 is expected to be set to either YES or NO
+(case insensitive). Its current value instead is $(eval echo \$$1).
+
+Please fix this error by setting the appropriate value in
+/etc/sbopkg/sbopkg.conf and/or in ~/.sbopkg.conf
+and restart $SCRIPT.
+
+EOF
+        exit 1
+    fi
+}
+
 load_repositories() {
     # Fill the REPOSITORIES array with the data from the .repo files