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Home: Perl Programming Help: Frequently Asked Questions:
Why don't my <<HERE documents work?



Jan 19, 2001, 3:04 PM

Post #1 of 1 (3764 views)
Why don't my <<HERE documents work? Can't Post

(From the Perl FAQ)

Why don't my <<HERE documents work?

Check for these three things:

1. There must be no space after the << part.
2. There (probably) should be a semicolon at the end.
3. You can't (easily) have any space in front of the tag.

If you want to indent the text in the here document, you can do this:

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

But the HERE_TARGET must still be flush against the margin. If you want that indented also, you'll have to quote in the indentation.

    ($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
$quote =~ s/\s*--/\n--/;

A nice general-purpose fixer-upper function for indented here documents follows. It expects to be called with a here document as its argument. It looks to see whether each line begins with a common substring, and if so, strips that off. Otherwise, it takes the amount of leading white space found on the first line and removes that much off each subsequent line.

    sub fix { 
local $_ = shift;
my ($white, $leader); # common white space and common leading string
if (/^\s*(?:([^\w\s]+)(\s*).*\n)(?:\s*\1\2?.*\n)+$/) {
($white, $leader) = ($2, quotemeta($1));
} else {
($white, $leader) = (/^(\s+)/, '');
return $_;

This works with leading special strings, dynamically determined:

    $remember_the_main = fix<<'    MAIN_INTERPRETER_LOOP'; 
@@@ int
@@@ runops() {
@@@ SAVEI32(runlevel);
@@@ runlevel++;
@@@ while ( op = (*op->op_ppaddr)() ) ;
@@@ return 0;
@@@ }

Or with a fixed amount of leading white space, with remaining indentation correctly preserved:

    $poem = fix<<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


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