Section 2.4. Finding the Length of a String

2.3. Using Here-Documents

If you want to represent a long string spanning multiple lines, you can certainly use a regular quoted string:

str = "Once upon a midnight dreary,        While I pondered, weak and weary..."

However, the indentation will be part of the string.

Another way is the here-document, a string that is inherently multiline. (This concept and term are borrowed from older languages and contexts.) The syntax is the << symbol, followed by an end marker, then zero or more lines of text, and finally the same end marker on a line by itself:

str = <<EOF Once upon a midnight dreary, While I pondered weak and weary,... EOF

Be careful about things such as trailing spaces on the final end marker line. Current versions of Ruby will fail to recognize the end marker in those situations.

Note that here-documents may be "stacked"; for example, here is a method call with three such strings passed to it:

some_method(<<str1, <<str2, <<str3) first piece of text... str1 second piece... str2 third piece of text. str3

By default, a here-document is like a double-quoted stringthat is, its contents are subject to interpretation of escape sequences and interpolation of embedded expressions. But if the end marker is single-quoted, the here-document behaves like a single-quoted string:

str = <<'EOF' This isn't a tab: \t and this isn't a newline: \n EOF

If a here-document's end marker is preceded by a hyphen, the end marker may be indented. Only the spaces before the end marker are deleted from the string, not those on previous lines.

str = <<-EOF   Each of these lines   starts with a pair   of blank spaces. EOF

Here is a style I personally like. Let's assume the existence of the margin method defined here:

class String   def margin     arr = self.split("\n")             # Split into lines     arr.map! {|x| x.sub!(/\s*\|/,"")}  # Remove leading characters     str = arr.join("\n")               # Rejoin into a single line     self.replace(str)                  # Replace contents of string   end end

I've commented this fairly heavily for clarity. Parts of it involve features explained elsewhere in this chapter or later chapters.

It's used in this way:

str = <<end.margin   |This here-document has a "left margin"   |at the vertical bar on each line.   |   |  We can do inset quotations,   |  hanging indentions, and so on. end

The word end is used naturally enough as an end marker. (This, of course, is a matter of taste. It "looks" like the reserved word end but is really just an arbitrary marker.) Each line starts with a vertical bar, which is then stripped off each line (along with the leading whitespace).