In VI, when an arrow key is pressed, a character (e.g. “A“) is sent.

That usually happens when vi is running in a mode that doesn’t understand your terminal’s arrow key escape sequences.

Here’s why:

• Arrow keys don’t send a single character; they send an escape sequence (for example, the Up arrow sends ESC [ A).

• If vi (or more commonly the very old ex/vi implementation, not vim) doesn’t recognize these escape sequences, it just displays the trailing characters like A, B, C, D (or sometimes M) instead of moving the cursor.

Common reasons

1. You’re actually running vi, not vim.
   Some minimal Linux/Unix systems only ship with the original BSD vi, which lacks proper arrow key support.

2. Terminal