shift contents of long $() into filter_ids()

This was prompted by the fact that posh does not deal with $()
that contains comments where the comment includes an odd number
of single-quotes. It seems to get befuddled into trying to find
the matching quote.
Regardless, making a function for filtering the unneeded ids
seems much neater than avoiding apostrophes,
so that's what I've done.

SSH-Copy-ID-Upstream: 3dab3366a584427045c8a690a93282f02c09cf24

contrib/ssh-copy-id

@@ -169,26 +169,16 @@ if [ -z "$(eval $GET_ID)" ] ; then
   exit 1
 fi
 
-# populate_new_ids() uses several global variables ($USER_HOST, $SSH_OPTS ...)
-# and has the side effect of setting $NEW_IDS
-populate_new_ids() {
+# filter_ids()
+# tries to log in using the keys piped to it, and filters out any that work
+filter_ids() {
   L_SUCCESS="$1"
   L_TMP_ID_FILE="$SCRATCH_DIR"/popids_tmp_id
   L_OUTPUT_FILE="$SCRATCH_DIR"/popids_output
 
-  # shellcheck disable=SC2086
-  if [ "$FORCED" ] ; then
-    NEW_IDS=$(eval $GET_ID)
-    return
-  fi
-
   # repopulate "$@" inside this function
   eval set -- "$SSH_OPTS"
 
-  printf '%s: INFO: attempting to log in with the new key(s), to filter out any that are already installed\n' "$0" >&2
-  # shellcheck disable=SC2086
-  NEW_IDS=$(
-    eval $GET_ID | {
   while read -r ID || [ "$ID" ] ; do
     printf '%s\n' "$ID" > "$L_TMP_ID_FILE"
 
@@ -216,8 +206,20 @@ populate_new_ids() {
 
     cat "$L_TMP_ID_FILE"
   done
-    }
-  )
+}
+
+# populate_new_ids() uses several global variables ($USER_HOST, $SSH_OPTS ...)
+# and has the side effect of setting $NEW_IDS
+populate_new_ids() {
+  if [ "$FORCED" ] ; then
+    # shellcheck disable=SC2086
+    NEW_IDS=$(eval $GET_ID)
+    return
+  fi
+
+  printf '%s: INFO: attempting to log in with the new key(s), to filter out any that are already installed\n' "$0" >&2
+  # shellcheck disable=SC2086
+  NEW_IDS=$(eval $GET_ID | filter_ids $1)
 
   if expr "$NEW_IDS" : "^ERROR: " >/dev/null ; then
     printf '\n%s: %s\n\n' "$0" "$NEW_IDS" >&2