How to change which characters are selected by double-clicking in xterm

Various terminal emulators on Linux (e.g. xterm, gnome-terminal, rxvt) have word selection: when you double-click a character, it selects the entire word containing the character. This blog post explains how to customize which characters are part of a word in xterm.

The various defaults are for ASCII characters (in addition to digits and the letters a-z and A-Z):

• gnome-terminal: # % & + , - . / = ? @ \ _ ~
• rxvt: ! # $ % + - . / : _
• xterm default: _
• xterm in Ubuntu: ! # % & + , - . / : = ? @ _ ~

It's possible to customize which characters are part of a word in xterm by specifying the charClass resource. The values :48 mean: consider these characters part of a word. Other numbers are character ranges, for example 43-47 mean the ASCII characters 43 (+), 44 (,), 45 (-), 46 (.) and 47 (/).

Here is how to trigger various default behaviors from the command-line:

• gnome-terminal: xterm -xrm '*.VT100.charClass: 35:48,37:48,38:48,43-47:48,61:48,63-64:48,92:48,95:58,126:48'
• rxvt: xterm -xrm '*.VT100.charClass: 33:48,35-37:48,43:48,45-47:48,58:48,95:58'
• xterm default: xterm -xrm '*.VT100.charClass: 95:48'
• xterm in Ubuntu: xterm -xrm '*.VT100.charClass: 33:48,35:48,37-38:48,43-47:48,58:48,61:48,63-64:48,95:48,126:48'

To save the setting permanently, add a line like this to your ~/.Xresources file (create it if it doesn't exist):

! Here is a pattern that is useful for double-clicking on a URL (default xterm in Ubuntu):
XTerm.VT100.charClass: 33:48,35:48,37-38:48,43-47:48,58:48,61:48,63-64:48,95:48,126:48

Make sure above that the line containing charClass doesn't start with !, because that would be a comment.

The change takes affect automatically the next time you log in. To make it take effect earlier (for all xterms you start), run: xrdb -merge ~/.Xresources