Fix handling of missing required env variable

Ensure the error message is displayed correctly when a required env
variable is missing: add missing "echo" command and put the variable
name in simple quotes instead of backticks so that it's not executed as
a command.

Fixes issue #1.

Author: bertrand-lorentz

8.0/scripts/___mysqlexport.sh

@@ -11,9 +11,9 @@ XDB_EXPORT_GZIP="$DB_EXPORT_GZIP"
 XDB_EXPORT=
 
 # Required env variables
-if [[ -z "$DB_NAME" ]]; then "ERROR: `DB_NAME` env variable is required."; exit 1; fi
-if [[ -z "$DB_USERNAME" ]]; then "ERROR: `DB_USERNAME` env variable is required."; exit 1; fi
-if [[ -z "$DB_PASSWORD" ]]; then "ERROR: `DB_PASSWORD` env variable is required."; exit 1; fi
+if [[ -z "$DB_NAME" ]]; then echo "ERROR: 'DB_NAME' env variable is required."; exit 1; fi
+if [[ -z "$DB_USERNAME" ]]; then echo "ERROR: 'DB_USERNAME' env variable is required."; exit 1; fi
+if [[ -z "$DB_PASSWORD" ]]; then echo "ERROR: 'DB_PASSWORD' env variable is required."; exit 1; fi
 
 # Optional env variables
 if [[ -z "$XDB_PROTO" ]]; then XDB_PROTO="tcp"; fi

8.0/scripts/___mysqlimport.sh

@@ -13,10 +13,10 @@ XDB_IMPORT_GZIP="$DB_IMPORT_GZIP"
 XDB_IMPORT=
 
 # Required env variables
-if [[ -z "$DB_NAME" ]]; then "ERROR: `DB_NAME` env variable is required."; exit 1; fi
-if [[ -z "$DB_USERNAME" ]]; then "ERROR: `DB_USERNAME` env variable is required."; exit 1; fi
-if [[ -z "$DB_PASSWORD" ]]; then "ERROR: `DB_PASSWORD` env variable is required."; exit 1; fi
-if [[ -z "$DB_IMPORT_FILE_PATH" ]]; then "ERROR: `DB_IMPORT_FILE_PATH` env variable is required."; exit 1; fi
+if [[ -z "$DB_NAME" ]]; then echo "ERROR: 'DB_NAME' env variable is required."; exit 1; fi
+if [[ -z "$DB_USERNAME" ]]; then echo "ERROR: 'DB_USERNAME' env variable is required."; exit 1; fi
+if [[ -z "$DB_PASSWORD" ]]; then echo "ERROR: 'DB_PASSWORD' env variable is required."; exit 1; fi
+if [[ -z "$DB_IMPORT_FILE_PATH" ]]; then echo "ERROR: 'DB_IMPORT_FILE_PATH' env variable is required."; exit 1; fi
 
 # Optional env variables
 if [[ -z "$XDB_PROTO" ]]; then XDB_PROTO="tcp"; fi