What are different ways to type in a literal character in Bash and how are they done?

Question

In Bash, to type in a literal TAB character:

• hitting tab key doesn't work but will only invoke completion of readline used by Bash
• Ctrl-V-tab works
• $(echo $'\t') works

Questions

• Is it correct that the third way is actually done by Bash interpreting $'\t' as an ANSI C string for the tab character?
• How is the second way done? Also by readline used by Bash?
• Generally what are some ways to type in a literal character?

Originated from: https://unix.stackexchange.com/a/458074/674

Answer 1

How it's made

The so called by you "literal characters" are implemented as ordinary Unicode charachters. Let's look how it works for Tabulation and New line. Check Tabulation hex-encoding:

printf $'\t' | hexdump

The output is

0000000 0009                                   
0000001

The output means the \t character is ordinary UTF-8 character U+0009. You can print it in such the way:

printf '\x00\x09'

or with echo:

echo -e '\u0009'

Consider the following example for New line character:

bob@alice:~$ printf $'\n' | hexdump
0000000 000a                                   
0000001
bob@alice:~$ printf '\x00\x0A empty lines are above and below'; echo $'\n'

 empty lines are above and below

bob@alice:~$ echo -e '\u000a empty line is above'

 empty line is above
bob@alice:~$ 

How to input Unicode characters

There is so called ComposeKey or MultiKey in Linux. The key can be defined in xorg.conf.d/10-keyboard.conf file, just add the line to file:

Option "xkbOptions" "grp:alt_shift_toggle,terminate:ctrl_alt_bksp,compose:menu"`

UTF-8 (Unicode) compose sequence hints can be found in Compose file:

less /usr/share/X11/locale/en_US.UTF-8/Compose

In GUI terminals also works CTRL+SHIFT+U keybinding - press it and you'll see u letter. Input 266a and complete it with Space or Enter key - the Eights Note sign appears.

Additional information

1. ANSI-C Quoting
2. Ubuntu - ComposeKey
3. Wikipedia - Compose key
4. How to set a Compose Key in Ubuntu 18.04