Perl Cookbook

Indenting Here Documents

Problem

When using the multiline quoting mechanism called a here document, the text must be flush against the margin, which looks out of place in the code. You would like to indent the here document text in the code, but not have the indentation appear in the final string value.

Solution

Use a s/// operator to strip out leading whitespace.

# all in one
($var = <<HERE_TARGET) =~ s/^\s+//gm;
    your text
    goes here
HERE_TARGET

# or with two steps
$var = <<HERE_TARGET;
    your text
    goes here
HERE_TARGET
$var =~ s/^\s+//gm;

Discussion

The substitution is straightforward. It removes leading whitespace from the text of the here document. The /m modifier lets the ^ character match at the start of each line in the string, and the /g modifier makes the pattern matching engine repeat the substitution as often as it can (i.e., for every line in the here document).

($definition = <<'FINIS') =~ s/^\s+//gm;
    The five varieties of camelids
    are the familiar camel, his friends
    the llama and the alpaca, and the
    rather less well-known guanaco
    and vicuña.
FINIS

Be warned: all the patterns in this recipe use \s , which will also match newlines. This means they will remove any blank lines in your here document. If you don’t want this, replace \s with [^\S\n] in the patterns.

The substitution makes use of the property that the result of an assignment can be used as the left-hand side of =~. This lets us do it all in one line, but it only works when you’re assigning to a variable. When you’re ...