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1.11. Indenting Here DocumentsProblemWhen 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. SolutionUse a # 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 $var =~ s/^\s+//gm; DiscussionThe substitution is straightforward. It removes leading whitespace from the text of the here document. The ($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 vicuсa. FINIS Be warned: all the patterns in this recipe use The substitution makes use of the property that the result of an assignment can be used as the left-hand side of Not to worry, though, because there's an easy way around this, particularly if you're going to do this a lot in the program. Just write a subroutine to do it: sub fix { my $string = shift; $string =~ s/^\s+//gm; return $string; } print fix(<<"END"); My stuff goes here END # With function predeclaration, you can omit the parens: print fix <<"END"; My stuff goes here END As with all here documents, you have to place this here document's target (the token that marks its end, ($quote = <<' FINIS') =~ s/^\s+//gm; ...we will have peace, when you and all your works have perished--and the works of your dark master to whom you would deliver us. You are a liar, Saruman, and a corrupter of men's hearts. --Theoden in /usr/src/perl/taint.c FINIS $quote =~ s/\s+--/\n--/; #move attribution to line of its own If you're doing this to strings that contain code you're building up for an Another embellishment is to use a special leading string for code that stands out. For example, here we'll prepend each line with if ($REMEMBER_THE_MAIN) { $perl_main_C = dequote<<' MAIN_INTERPRETER_LOOP'; @@@ int @@@ runops() { @@@ SAVEI32(runlevel); @@@ runlevel++; @@@ while ( op = (*op->op_ppaddr)() ) ; @@@ TAINT_NOT; @@@ return 0; @@@ } MAIN_INTERPRETER_LOOP # add more code here if you want } Destroying indentation also gets you in trouble with poets. sub dequote; $poem = dequote<<EVER_ON_AND_ON; Now far ahead the Road has gone, And I must follow, if I can, Pursuing it with eager feet, Until it joins some larger way Where many paths and errands meet. And whither then? I cannot say. --Bilbo in /usr/src/perl/pp_ctl.c EVER_ON_AND_ON print "Here's your poem:\n\n$poem\n"; Here is its sample output:
The following sub dequote { local $_ = shift; my ($white, $leader); # common whitespace and common leading string if (/^\s*(?:([^\w\s]+)(\s*).*\n)(?:\s*\1\2?.*\n)+$/) { ($white, $leader) = ($2, quotemeta($1)); } else { ($white, $leader) = (/^(\s+)/, ''); } s/^\s*?$leader(?:$white)?//gm; return $_; } If that pattern makes your eyes glaze over, you could always break it up and add comments by adding if (m{ ^ # start of line \s * # 0 or more whitespace chars (?: # begin first non-remembered grouping ( # begin save buffer $1 [^\w\s] # one byte neither space nor word + # 1 or more of such ) # end save buffer $1 ( \s* ) # put 0 or more white in buffer $2 .* \n # match through the end of first line ) # end of first grouping (?: # begin second non-remembered grouping \s * # 0 or more whitespace chars \1 # whatever string is destined for $1 \2 ? # what'll be in $2, but optionally .* \n # match through the end of the line ) + # now repeat that group idea 1 or more $ # until the end of the line }x ) { ($white, $leader) = ($2, quotemeta($1)); } else { ($white, $leader) = (/^(\s+)/, ''); } s{ ^ # start of each line (due to /m) \s * # any amount of leading whitespace ? # but minimally matched $leader # our quoted, saved per-line leader (?: # begin unremembered grouping $white # the same amount ) ? # optionalize in case EOL after leader }{}xgm; There, isn't that much easier to read? Well, maybe not; sometimes it doesn't help to pepper your code with insipid comments that mirror the code. This may be one of those cases. See AlsoThe "Scalar Value Constructors" section of perldata (1) and the "Here Documents" section of Chapter 2 of Programming Perl; the |