Datasheet

UNDO
The UNDO command displays the following options at the command prompt:
Auto/Control/BEgin/End/Mark/Back<Number>:
Auto Auto requires an additional specification of On or Off. When Auto is on, any opera-
tion taken from the menu, no matter how complicated, is treated as a single command,
reversible by a single U command.
Back Back takes the drawing back to the state it was in when the most recent mark was
entered. If you don’t enter a mark, the drawing goes back to the beginning of the editing
session. AutoCAD automatically places marks when some commands are used, but nor-
mally you must place them yourself. You can place multiple marks and UNDO each.
Control Control limits the UNDO operation or disables it completely. It offers the follow-
ing options:
• All enables the full UNDO feature.
• None disables U and UNDO commands.
• One limits U and UNDO to a single operation.
BEgin and End BEgin and End cause a group of commands to be treated as a single com-
mand for the purposes of U and UNDO. A group, once ended, is always treated as a single,
indivisible operation.
Mark Mark makes a special mark in the undo information, to which you can later back up
with the Back option. If you’re about to go off on a design tangent, you may want to set a
mark with UNDO so you can return to that point quickly if the tangent doesn’t work out.
Number Number (default is 1) specifies the number of preceding operations to be
undone. UNDO 1 is the equivalent of the U command. When you use a different value,
20 for example, 20 operations are undone at once. Typing REDO restores all 20. Using this
option allows you to search back through the drawing history (only during the current
editing session) for a specific point in the design process by typing in large values. Don’t
forget to save the drawing before doing this.
You can click the down arrow next to the Undo button to see a command history and select
the command you want to go back to. The Redo button has a similar command history.
This is useful when you’re writing an AutoLISP program. Place an UNDO BEgin at the begin-
ning of the program and an UNDO End at the end. If the user doesn’t like what the program
did, it only takes one U to undo it. Otherwise, a separate UNDO is required for each step exe-
cuted by the AutoLISP program.
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