Course of Raku / Advanced / More about built-in types / Quoting constructs 🆕

Heredocs

A heredoc is a quoting form for multi-line text. Instead of delimiters around the text, you give a terminator word with :to, and the string runs from the next line until a line containing just that word:

my $text = q:to/END/;
Hello,
World!
END

print $text;

This prints:

Hello,
World!

The terminator (END here — any word will do) marks where the text ends. Note the print: the text keeps the newline that sits before the terminator, so it already ends in a line break — using say would add a second one and leave a trailing blank line. Because the heredoc starts with q:to, the text is not interpolated; use qq:to to interpolate variables:

my $name = 'Anna';

my $greeting = qq:to/EOF/;
Dear $name,
Welcome!
EOF

print $greeting;

A useful detail: the indentation of the closing terminator is stripped from every line of the text. This lets you indent a heredoc to match the surrounding code without that indentation ending up in the string:

sub greeting {
    return q:to/END/;
        Hello,
        World!
        END
}

print greeting;

This prints the same Hello, and World! as the first example. Here the closing END is indented by eight spaces, so eight spaces are removed from each line, and the returned string is just Hello,\nWorld! with no leading spaces.

The closing terminator sets how much is stripped, so every line of the text must be indented at least that much. If a line has fewer leading spaces, Raku cannot remove the full amount and warns — Asked to remove 8 spaces, but the shortest indent is 4 spaces. Keep the terminator no deeper than the shallowest line to avoid it. Heredocs are the natural choice for templates, messages, and any block of text that spans several lines.

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