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BK LISP: Break a Line at an Intersection in AutoCAD

September 18, 2020

Last updated July 28, 2026

This breaks a line where another line crosses it, and it sets the object snap for you so the break lands exactly on the intersection rather than near it.

That second part is the whole value. Breaking a line at a crossing is a two-command job otherwise — set the snap, run BREAK, use the First point option, pick, then pick the same point again — and if you forget the snap you get a break that looks right on screen and is a fraction of a millimetre off in the drawing. This does it in one command with the snap handled.

The file dates itself to 11 April 1989 and calls itself version 1.2.

The command is BK

Not BRK, which is what the download and the listing are called. The file’s own first line is a comment reading BK, so the author knew — it just never made it onto the label.

Two letters, so check it against your own aliases before loading.

How the zero-length break works

Worth understanding because it is the same trick the BreakPoint routine here uses, and it is a useful thing to know in its own right.

AutoCAD’s BREAK normally removes a piece of the line between two points. To split a line without removing anything, you give it the same point twice — the gap is zero length, so the line becomes two lines meeting at that spot with nothing missing.

This routine does that by supplying the point once and then using AutoCAD’s shorthand for “the same point again” as the second answer. So one pick from you becomes two identical points in the command.

It borrows your object snap and gives it back

Worth crediting, because plenty of routines in this library do the first half and forget the second.

The routine saves your running object snap setting, switches it to intersection only for the duration, and restores your original setting when it finishes. Command echo is handled the same way. So it does not leave your drawing environment altered behind it.

The one gap is that there is no error handler, so cancelling partway through will leave the snap set to intersection. If you escape out of it, reset your snaps.

How to load it

Unzip BRK.zip and load BRK.LSP with APPLOAD, or put it in the Startup Suite. No support files. Our AutoLISP guide covers loading.

Step-by-step usage

  1. Type BK.
  2. At “Choose Line to Break…” click the line you want split.
  3. At “Pick Break Point..” click near the intersection. The snap will pull it exactly onto the crossing point.
  4. The line is now two lines. Nothing is removed.

Because the snap is forced to intersection only, the pick will not land anywhere else — which is helpful when the crossing is in a crowded area, and a nuisance if what you actually wanted was a break somewhere other than a crossing. For that, use BreakPoint instead, which leaves your snaps alone.

Compatibility notes

1989, which puts it among the oldest files on this site. It reads and writes two system variables and drives the BREAK command with options that have not changed in the intervening decades, so there is very little in it that could age badly.

Plain AutoLISP with no dialog boxes and no Express Tools calls, so nothing requires the full product; LT users on LT 2024 or later, the release that brought AutoLISP to LT, should be able to run it. See what runs on AutoCAD LT.

Download

Name: BRK
Description: Will break a line at an intersection with another line.
Automatically sets OSNAPs to intersect.
Type: AutoCAD AutoLISP Routine
Author: Anon
File Size: 1 Kb
Cost: Free
Worked on: AutoCAD
Download File: BRK.zip

Related routines

  • BreakPoint — the same zero-length break without forcing a snap.
  • Trim to Point — trim rather than split.
  • FZ — make two lines meet at a sharp corner instead.

References

  • AutoLISP: the complete guide
  • Free LISP routines library
  • AutoLISP on AutoCAD LT

Filed Under: AutoLISP Routines

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