Don't gen string that ends with hyphen (#1899)

For CLI tests

fixes #1864

tests/cli/test_helper/fluvio_dev.bash

@@ -17,16 +17,20 @@ function debug_msg() {
 
 # Note: We only generate strings w/ *lowercase* alphanum or '-'
 # for topic naming compatibility
+# We don't check for minimum length, but $DEFAULT_LEN >= 3
+# or `shuf` will err when requested $BODY length less than zero
 function random_string() {
     DEFAULT_LEN=7
     STRING_LEN=${1:-$DEFAULT_LEN}
 
-    # Ensure we don't end up with a string that starts with '-'
+    # Ensure we don't end up with a string that starts or ends with '-'
+    # https://github.com/infinyon/fluvio/issues/1864
 
-    STRING1=$(shuf -zer -n1 {a..z} {0..9})
-    STRING2=$(shuf -zer -n"$(($STRING_LEN-1))" {a..z} {0..9} "-")
+    HEAD=$(shuf -zer -n1 {a..z} {0..9})
+    BODY=$(shuf -zer -n"$(($STRING_LEN-2))" {a..z} {0..9} "-")
+    FOOT=$(shuf -zer -n1 {a..z} {0..9})
 
-    RANDOM_STRING=$STRING1$STRING2
+    RANDOM_STRING=$HEAD$BODY$FOOT
 
     if [[ -n $DEBUG ]]; then
         echo "# DEBUG: Random str (len: $STRING_LEN): $RANDOM_STRING" >&3