2009-07-29
The shift-selection trick in X terminal programs
Seeing this today
reminded me of a relatively obscure feature and counter-feature in
xterm and similar imitators like gnome-terminal and konsole.
First, the feature (sometimes 'feature'): in order to let text mode
programs still have clickable objects, xterm lets programs steal left
mouse (button-1) clicks; instead of selecting text, the program gets
escape sequences that tell it about the click and it can do whatever it
wants with them. The most obvious application is text-mode web browsers
like links, which uses it to let you click on links.
(The Xterm Control Sequences documentation calls this 'mouse tracking'.)
This spawned an immediate demand for a counter-feature, and so in
xterm and its imitators shift plus left mouse button always selects
text, even if a program has put xterm in this special mouse tracking
mode. In xterm, all of the usual double and triple click selection
tricks work when shifted; your mileage may vary in gnome-terminal et al.
This doesn't seem to be documented in the xterm manpage, so I'm
not sure where I learned it; it may have been ambient X knowledge
at some point back in the days, and I just picked it up. It's
fortunate that it seems to have been well enough known to be
copied by the people writing gnome-terminal, konsole, and so on.
(xterm has a great deal of peculiar features that are at best half-known these days, or
that usually take careful study of the manpage to spot.)