DECALN — Screen Alignment Display

Sequence	ESC # 8
Bytes	0x1B 0x23 0x38
Category	ESC (DEC private)
Mnemonic	DECALN
Otty support	✓ Implemented

Description

Fills the entire visible screen with the character E (uppercase) using the default attributes. Introduced on DEC VT terminal hardware so technicians could verify screen geometry and convergence.

After execution:

• The cursor is moved to home (row 1, column 1).
• Every cell of the active viewport is replaced with E.
• Active SGR attributes (color, weight, etc.) are reset for the filled cells.
• Scrollback is not affected.

Example

Send the sequence from any program:

printf '\e#8'

The visible terminal area fills with E characters:

EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
EEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEEE
…

You can drive it through the Otty CLI to test against a managed session:

otty cli send-raw $'\e#8'

Notes

• Only the visible viewport is affected; scrollback remains intact.
• DECALN does not change the cursor style or scrolling region.
• Combined with DECSTR (Soft Reset, ESC [ ! p), DECALN is the canonical way to put a terminal into a known-good state during tests.

Related

• ESC Sequences — the rest of the single-ESC category.
• DECSTR — soft reset, often paired with DECALN in tests.
• RIS — full reset to power-on state.