Course of Raku / Essentials / Strings

Escaping special characters

Imagine you want to print a price label, and you keep both the name of the product and its price in scalar variables?

my $product = 'Electricity';
my $price = 3.14;

How do you print the label if the price is meant to be in dollars? The expected output is: Electricity costs $3.14. A dollar sign in double-quoted strings is an indicator of a variable to be interpolated. To print the $ character itself, you need to escape it:

say "$product costs \$$price";

Of course, you can use string concatenation and avoid escaping $:

say $product ~ ' costs $' ~ $price;

This variant prints exactly the same string, but interpolation look more natural and easier to read. Note that the $ character was neither interpolated nor escaped in a single-quoted string: ' costs $'. That’s the main difference. Special characters in single quotes appear as-is.

Here is a few more special characters that have special meaning in double-quoted strings:

The way you quote the string defines how Raku treats special characters. Consider these two examples:

say 'One\nTwo';
say "Three\nFour";

If you run this program, you will see that the first string appears as is on a single line. The second string was split into two pieces:

One\nTwo
Three
Four

In double quotes, a special sequence \n was processed as a newline character, while in a string in single quotes it was a regular sequence of two characters: \ and n.

There’s an interesting exception for ' and \. In single quotes, you can escape a single quote by prefixing it with another \:

say '\''; # '

A backslash also has to be escaped if a single quote follows it:

say 'a\b\c\\'; # a\b\c\

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