How do I rename many layers at once in AutoCAD?

What cadssistant does

1. Reads the layer table with tblnext and matches names with wcmatch "X-*".
2. Runs -RENAME Layer old new for each match in one AutoLISP pass; a target that already exists is skipped and reported.
3. Replies with old → new for every layer. Xref-dependent layers (names containing |) are left alone.

The same task in AutoLISP

(progn
  (setq def (tblnext "LAYER" T) names nil done nil)
  (while def
    (if (wcmatch (cdr (assoc 2 def)) "X-*") (setq names (cons (cdr (assoc 2 def)) names)))
    (setq def (tblnext "LAYER")))
  (foreach nm names
    (if (not (tblsearch "LAYER" (strcat "A-" (substr nm 3))))
      (progn
        (command "_.-RENAME" "_LA" nm (strcat "A-" (substr nm 3)))
        (setq done (cons nm done)))))
  done)

Collects the matching names first, then renames each unless the target exists. Returns the layers it renamed.

Good to know

• Renaming to a layer standard: paste the old-to-new mapping as a table in the message and it uses that instead of a pattern.
• Say "merge instead" and it runs LAYMRG, which moves the objects onto the target and deletes the source, a different operation.

More in edit in bulk

• How do I move all objects of one type to another layer in AutoCAD?
• How do I change the height of all text in an AutoCAD drawing at once?
• How do I replace one block with another throughout an AutoCAD drawing?
• How do I delete everything on a layer and purge it in AutoCAD?