How do I hatch a selected area with a pattern in AutoCAD from a sentence?

What cadssistant does

1. Takes the boundary from your selection, or asks "Select the boundary:" in the drawing.
2. Runs AutoCAD's command-line -HATCH, as one command or one AutoLISP form: pattern ANSI31, scale 1, angle 0, then Select objects with your selection. The hatch is associative to that boundary when HPASSOC is on, which is the default.
3. Replies with the pattern, scale and angle it used. Revert in the chat removes it if the scale is wrong; say the scale next time.

By hand, at the command line

Command: -HATCH
Specify internal point or [Properties/Select objects/...]: P
Enter a pattern name or [?/Solid/User defined] <ANSI31>: ANSI31
Specify a scale for the pattern <1.0000>: 1
Specify an angle for the pattern <0>: 0
Specify internal point or [Properties/Select objects/...]: S
Select objects: (pick the boundary) ↵
Specify internal point or [Properties/Select objects/...]: ↵

By hand: the command-line HATCH, which is also what cadssistant drives.

Good to know

• A boundary made of separate lines must be closed with no gaps, or HATCH reports an open boundary. Say "join the lines first" and it runs PEDIT Join before hatching.
• Pattern names are the ones in your acad.pat or acadiso.pat: ANSI31, ANSI32, AR-CONC, DOTS, SOLID and so on. An unknown name fails on the command line and it reports the error.

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