TIL - X11 Clipboard System

28 Nov, 2024

Key Points

Unix/X11 maintains 3 separate clipboards:

• CLIPBOARD (Ctrl+C/V)
• PRIMARY (highlight + middle click)
• SECONDARY (rarely used)

Clipboard doesn't store data directly - just references to source apps. Data transfer happens only on paste.

Clipboard Formats

Apps advertise available formats using MIME types. Common formats:

• text/plain
• text/html
• application/octet-stream (raw bytes)
• UTF8_STRING
• image/png
• text/uri-list

Debugging Commands

# See available formats
xclip -selection clipboard -o -t TARGETS

# Get specific format
xclip -selection clipboard -o -t text/plain
xclip -selection clipboard -o -t text/html
xclip -selection clipboard -o -t application/octet-stream

# Format HTML/XML output
xclip -selection clipboard -o -t text/html | tidy -qi --wrap 0
xclip -selection clipboard -o | xmllint --format -