^U in readline isn't an emacs command (that keystroke does something else in emacs); it's the old teletype protocol for line input. So if you aren't using read

^U in readline isn't an emacs command (that keystroke does something else in emacs); it's the old teletype protocol for line input. So if you aren't using readline, ^U deletes everything back to the beginning of the line. Readline preserves that because us pre-readline old farts have it wired into our fingers. Before display terminals there were just printing terminals: IIRC # deleted a character and @ everything to the beginning of the line. This goes back to Multics and was carried forward in early releases of Unix at Bell Labs. This is obviously pretty inconvenient when you have a display terminal but I am pretty sure that code remains in the bowels of the BSD TTY IO system at least and can probably be enabled. Maybe it even survived into linux for some compatibility reasons. Also I WUZ THERE and I think Chet has it backwards on the POSIX controls issue: bfox talked about the TWENEX line input JSYS that had that stuff built in (I believe it was also, perhaps even earlier, in VMS, and maybe TENEX, and surely he had talked to some of those folks too)