How to compose key in Linux

Question

This topic has been addressed on quite a few web pages of this website, however I do not yet understand the full extent of the things that we might be able to do with the Compose key. A user here has explained in How to type unicode characters in KDE? that, for example, we can do the following:

* Compose, v, C → Č
* Compose, ´, E → É
* Compose, _, u → ū
* Compose, ^, i → î
* Compose, ,, S → Ş
* Compose, +, o → ơ
* Compose, ;, a → ą
* Compose, U, g → ğ
* Compose, ", u → ü
* Compose, °, A → Å
* Compose, ~, N → Ñ
* Compose, +, - → ±
* Compose, ., > → ›
* Compose, ., . → …
* Compose, ., = → •
* Compose, P, ! → ¶
* Compose, !, ^ → ¦
* Compose, !, ! → ¡
* Compose, ?, ? → ¿
* Compose, s, s → ß
* Compose, o, e → œ
* Compose, O, E → Œ
* Compose, a, e → æ
* Compose, A, E → Æ

My impression from the above example is that we can combine two keys to produce the characters. Now, my questions are as follows:

1. Is it possible to combine multiple keys (for example, four keys) to achieve typing a greater range of Unicode characters?

2. Is it possible to define the key combinations arbitrarily? For example, if you press Ctrl+I+N+T to make an integral sign appear?

3. What about exotic characters? For example, the character ɔ is Unicode, but if we place a tilde sign over it, it’s not Unicode. So, can we define key sequences for these non-Unicode characters as well?

Answer 1

1. Yes. Via the use of a customized ~/.XCompose file (or whatever file is pointed to by $XCOMPOSEFILE one can create keymaps of seemingly arbitrary length; the following line

   <Multi_key> <l> <a> <l> <l> <l> : "lock and load little lizard"

   will, when one uses Compose, l, a, l, l, l will spout the quote from Gex.

2. Maybe? I'm not sure what an 'integral sign' sign is, but it seems this is the case, as the above example is cooked straight out of my own noggin, tested in xterm to work.

3. I don't think one can arbitrarily mash together characters with compose keys; eg, ñ is not an n with a tilde over it, it is a long established character in its own right to spanish speakers, called what I can best spell as an en-yay, and is needed to type valid spanish. Your backwards c+~ combo, afaik, is of no import to any language in the world, so the nice folks who developed X.org had no reason to include it.

Answer 2

SHIFT-CONTROL-U-hexidecimal-space will give you Unicode symbols. I used this on Windows years back and it still works for me on Linux using XFCE4. I think I remember this working on KDE as well.

For Unicode tables, I generally use Unicode Charts as a resource.

In KDE if I remember correctly, as it has been a while, I was forced to use the numeric keypad. The top row numbers would not work for it.