UNDO in AutoCAD

UNDO takes back commands. A step is a whole command: everything one LINE drew goes at once, however many segments it had, and so does whatever a command set, such as LTSCALE. UNDO writes its current settings, then asks for the number of operations to undo or an option; Enter takes back one. It writes the names of the commands it took back on one line, CIRCLE LINE, and Everything has been undone when it runs out; after that, Nothing to undo. A command that changed nothing, such as ID or LIST, is a step too, and so is what ZOOM and PAN did to the view.

U is the short form: one step back, no question. Ctrl+Z at the Command prompt runs U; inside a command it is that command's own Undo, as AutoCAD's macro types it: LINE takes back its last segment and goes on. REDO, right after, puts back what the last U or UNDO took.

• Command: UNDO
• Panel: Inquiry & view
• Try it: Open the editor, type UNDO and press Enter.

At the command line

The engine draws it and writes its history as you would type it: the prompts in AutoCAD 2027's order, with the same option letters.

Options

Auto (A)

Asks ON or OFf, offering the current setting, which the settings line then shows. In AutoCAD it makes one step of the commands a menu item runs; no menu here runs more than one, so here it joins nothing.

Control (C)

Asks how much undo to keep, All by default. None drops every step kept and turns undo off: U then says U command disabled. Use UNDO command to turn it on, and UNDO asks for Control at once. One keeps only the last step, and UNDO then asks for 1 or Control. All turns full undo back on. Combine says whether consecutive ZOOMs and PANs are one step, and Layer whether consecutive edits in the Layer Properties Manager are, Yes by default for both. The settings are the drawing's, and not saved with it: a new or opened drawing starts at All, Combine Yes and Layer Yes.

BEgin (BE)

Starts a group: the commands run until End make one step, which U takes back whole and names GROUP with them. While a group is open, U, a number and Back stop at its start. BEgin with a group open closes it first.

End (E)

Closes the group BEgin opened.

Mark (M)

Leaves a mark in the steps. Back, U and a number stop at it, with Mark encountered.

Back (B)

Takes back every step to the last mark, and the mark with them. With no mark, it asks whether to undo everything, Yes by default.

What it does not do yet

Auto joins nothing, as no menu here runs more than one command. Combine and Layer last the browser session, where AutoCAD keeps them from one session to the next. The top bar's Undo and Redo buttons write nothing in the history, where AutoCAD's Quick Access Toolbar writes its own. Ctrl+Shift+Z redoes too, silently, though AutoCAD binds nothing to it.

What it does and still lacks, in detail (in English)

Questions

What is the shortcut for UNDO in AutoCAD?

Ctrl+Z, or U then Enter: one step back. UNDO has no alias; type it in full for a number of steps or its options, or _UNDO in any language of AutoCAD.

What is the difference between U and UNDO?

U takes back the last command and asks nothing. UNDO asks how many to take back, and has Mark and Back to go back to a point you marked, BEgin and End to make several commands one step, and Control to limit undo or turn it off.

How do I undo several commands at once?

Type UNDO and the number of commands, such as 5. Or choose Mark before a series you may want to drop, and Back to go back to it.

Why is the UNDO command not working?

Undo was turned off with Control None: U says so, and UNDO asks for Control. Answer All to turn it back on. Steps taken before that are gone.

How do I redo what I undid?

REDO right after U or UNDO puts back the whole of it. Ctrl+Y redoes one step at a time.

Related commands

• U: Undo the last action
• REDO in AutoCAD
• MREDO: Multiple redo
• ERASE in AutoCAD