Entering Unicode Characters

Input methods for unicode characters in editors and the shell

Perl 6 allows the use of unicode characters as variable names. Many operators are defined with unicode symbols (in particular the set/bag operators) as well as some quoting constructs. Hence it is good to know how to enter these symbols into editors, the Perl 6 shell and the command line, especially if the symbols aren't available as actual characters on a keyboard.

General information about entering unicode under various operating systems and environments can be found on the Wikipedia unicode input page.

XCompose (Linux)

Xorg includes digraph support using a Compose key . The default of AltGr + Shift can be remapped to something easier such as Capslock. In GNOME 2 and MATE this can be setup under Preferences → Keyboard → Layouts → Options → Position of Compose Key. So, for example, to input »+« you could type CAPSLOCK > > + CAPSLOCK < <

XCompose allows customising the digraph sequences using a .XCompose file and https://github.com/kragen/xcompose/blob/master/dotXCompose is an extremely complete one. In GNOME, XCompose was overridden and replaced with a hardcoded list, but it is possible to restore XCompose by setting GTK_IM_MODULE=xim in your environment. It might be necessary to install a xim bridge as well, such as uim-xim.

Getting Compose working in all Programs

You may have issues using the compose key in all programs. In that case you can try ibus.

    input_module=xim
    export GTK_IM_MODULE=$input_module
    export XMODIFIERS=@im=$input_module
    export QT_IM_MODULE=$input_module

If you want this to be for all users you can put this in a file /etc/profile.d/compose.sh, which is the easiest way, since you won't have to deal with how different GUI environments set up their environment variables.

If you use KDE you can put this file in ~/.config/plasma-workspace/env/compose.sh and that should work. Other desktop environments will be different. Look up how to set environment variables in yours or use the system-wide option above.

ibus

If you have problems entering high codepoint symbols such as 🐧 using the xim input module, you can instead use ibus. You will have to install the ibus package for your distribution. Then you will have to set it to start on load of your Desktop environment. The command that needs to be run is:

    ibus-daemon --xim --verbose --daemonize --replace

Setting --xim should also allow programs not using ibus to still use the xim input method and be backward compatible.

KDE

If you are using KDE, open the start menu and type in “Autostart” and click Autostart which should be the first result. In the settings window that opens, click Add program, type in ibus-daemon and click OK. Then go into the Application tab of the window that pops up. In the Command field, enter in the full ibus-daemon command as shown above, with the --desktop option set to --desktop=plasma. Click OK. It should now launch automatically when you log in again.

Editors and shells

Vim

In Vim, unicode characters are entered (in insert-mode) by pressing first Ctrl-V (also denoted ^V), then u and then the hexadecimal value of the unicode character to be entered. For example, the Greek letter λ (lambda) is entered via the key combination:

^Vu03BB

You can also use Ctrl-K/^K along with a digraph to type in some characters. So an alternative to the above using digraphs looks like this:

^Kl*

The list of digraphs Vim provides is documented here; you can add your own with the :digraph command.

Further information about entering special characters in Vim can be found on the Vim Wikia page about entering special characters.

Emacs

In Emacs, unicode characters are entered by first entering the chord C-x 8 RET at which point the text Unicode (name or hex): appears in the minibuffer. One then enters the unicode code point hexadecimal number followed by the enter key. The unicode character will now appear in the document. Thus, to enter the Greek letter λ (lambda), one uses the following key combination:

C-x 8 RET 3bb RET

Further information about unicode and its entry into Emacs can be found on the Unicode Encoding Emacs wiki page.

You can also use RFC 1345 character mnemonics by typing:

C-x RET C-\ rfc1345 RET

Or C-u C-\ rfc1345 RET.

To type special characters, type & followed by a mnemonic. Emacs will show the possible characters in the echo area. For example, Greek letter λ (lambda) can be entered by typing:

&l*

You can use C-\ to toggle input method.

Another input method you can use to insert special characters is TeX. Select it by typing C-u C-\ TeX RET. You can enter a special character by using a prefix such as \. For example, to enter λ, type:

\lambda

To view characters and sequences provided by an input method, run the describe-input-method command:

C-h I TeX

Unix shell

At the bash shell, one enters unicode characters by using entering Ctrl-Shift-u, then the unicode code point value followed by enter. For instance, to enter the character for the element-of operator (∈) use the following key combination (whitespace has been added for clarity):

Ctrl-Shift-u 2208 Enter

This also the method one would use to enter unicode characters into the perl6 REPL, if one has started the REPL inside a Unix shell.

Screen

GNU Screen does sport a digraph command but with a rather limited digraph table. Thanks to bindkey and exec an external program can be used to insert characters to the current screen window.

bindkey ^K exec .! digraphs

This will bind control-k to the shell command digraphs. You can use digraphs if you prefer a Perl 6 friendly digraph table over RFC 1345 or change it to your needs.

Unicode characters useful in Perl 6

smart quotes

These characters are used in different languages as quotation marks. In Perl 6 they are used as quoting characters

Constructs such as these are now possible:

say What?!;
say Whoa!“;
say „This works too!;
say There are just too many ways;
say here: no problem at all!# You can nest them! 

This is very useful in shell:

perl6 -e 'say ‘hello world’'

since you can just copy and paste some piece of code and not worry about quotes.

Guillemets

These characters are used in French and German as quotation marks. In Perl 6 they are used as interpolation word quotes, hyper operators and as bracket alternative in POD6.

symbol unicode code point ascii equivalent
« U+00AB <<
» U+00BB >>

Thus constructs such as these are now possible:

say (12) »+« (34);     # OUTPUT: «(4 6)␤» - element-wise add 
[123] »+=» 42;         # add 42 to each element of @array 
say «moo»;                 # OUTPUT: «moo␤» 
 
my $baa = "foo bar";
say «$baa $baa ber».perl;  # OUTPUT: «("foo", "bar", "foo", "bar", "ber")␤» 

Set/bag operators

The set/bag operators operators all have set-theory-related symbols, the unicode code points and their ascii equivalents are listed below. To compose such a character, it is merely necessary to enter the character composition chord (e.g. Ctrl-V u in Vim; Ctrl-Shift-u in Bash) then the unicode code point hexadecimal number.

operator unicode code point ascii equivalent
U+2208 (elem)
U+2209 !(elem)
U+220B (cont)
U+220C !(cont)
U+2286 (<=)
U+2288 !(<=)
U+2282 (<)
U+2284 !(<)
U+2287 (>=)
U+2289 !(>=)
U+2283 (>)
U+2285 !(>)
U+227C (<+)
U+227D (>+)
U+222A (|)
U+2229 (&)
U+2216 (-)
U+2296 (^)
U+228D (.)
U+228E (+)

Mathematical symbols

Wikipedia contains a full list of mathematical operators and symbols in unicode as well as links to their mathematical meaning.

Greek characters

Greek characters may be used as variable names. For a list of Greek and Coptic characters and their unicode code points see the Greek in Unicode Wikipedia article.

For example, to assign the value 3 to π, enter the following in Vim (whitespace added to the compose sequences for clarity):

my $Ctrl-V u 03C0 = 3;  # same as: my $π = 3;
say $Ctrl-V u 03C0;     # 3    same as: say $π;

Superscripts and subscripts

A limited set of superscripts and subscripts can be created directly in unicode by using the U+207x, U+208x and (less often) the U+209x ranges. However, to produce a value squared (to the power of 2) or cubed (to the power of 3), one needs to use U+00B2 and U+00B3 since these are defined in the Latin1 supplement Unicode block.

Thus, to write the Taylor series expansion around zero of the function exp(x) one would input into e.g. vim the following:

exp(x) = 1 + x + xCtrl-V u 00B2/2! + xCtrl-V u 00B3/3!
+ ... + xCtrl-V u 207F/n!
# which would appear as
exp(x) = 1 + x + x²/2! + x³/3! + ... + xⁿ/n!

Or to specify the elements in a list from 1 up to k:

ACtrl-V u 2081, ACtrl-V u 2082, ..., ACtrl-V u 2096
# which would appear as
A₁, A₂, ..., Aₖ