tex-sx_readline

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> can latex in principle be built with readline support for keyboard shell
> interaction?

Some clarification in advance, Latex is just a format running on some TeX
interpreter. That means: byte code, not native code. As such, Latex has no
concept of *linking* a library. That needs to be done one layer below.

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Linking readline would violate the core principles of Luatex and Pdftex. (I
don’t know about Xetex -- perhaps they don’t like the license.) On the one hand
it means introducing a runtime dependency, on the other hand the library remains
platform specific, regardless of how widespread and popular it is. Not the best
foundation for extending a feature as controversial as the interactive mode!

An interactive interpreter without readline is quite inconvenient, though.
Luckily, that usability gap can be closed quite easily by installing the
``rlwrap(1)`` utility. It takes an existing, dumb interpreter and transparently
adds a readline layer over the input. This does not affect the output except
for what readline would do, e. g. displaying the “insert mode” indicator
(``show-mode-in-prompt``) -- so best avoid it in your scripts.