组合键

What is a Compose Key?

The Compose key is a special keyboard key (or a regular key designated as Compose in software) that initiates a multi-keystroke sequence for typing special characters. After pressing Compose, the user types a sequence of ordinary keys — and the OS combines them into a single special character. No key needs to be held simultaneously; Compose acts as a latch, waiting for the sequence to complete.

For example: Compose, then e, then ' produces é. Compose, then c, then , produces ç. Compose, then <, then < produces «. The Compose key is particularly popular in Unix/Linux environments but is also available on macOS and Windows with third-party tools.

How Compose Sequences Work

The Compose system uses a compose table — a list of sequences and their resulting characters. On Linux/X11 systems, the default compose table is usually at /usr/share/X11/locale/en_US.UTF-8/Compose and contains thousands of entries. Users can create custom sequences in ~/.XCompose.

Setting Up a Compose Key

Linux (X11/Wayland): In GNOME, go to Settings → Keyboard → Special Character Entry → Compose Key. Common choices for the physical key: Right Alt, Caps Lock, Menu key, Right Ctrl.

Command line (X11):

# Set Compose to Right Alt for current session
setxkbmap -option compose:ralt

# Persistent: add to /etc/default/keyboard
XKBOPTIONS="compose:ralt"

macOS: Not built in. Use the free Ukelele app or install X Compose tools via Homebrew. The dead-key system (Option + key) is more native on macOS.

Windows: The WinCompose application adds a Compose key that uses the same X11 compose table format.

Custom Compose Sequences

On Linux, ~/.XCompose lets you define personal sequences:

# ~/.XCompose
include "%L"   # include default system sequences

# Custom entries
<Multi_key> <e> <m> : "📧"    # email emoji
<Multi_key> <t> <h> <e> : "the"  # abbreviation expansion
<Multi_key> <minus> <gt> : "→"   # arrow

Quick Facts