Perl in a Nutshell, 2nd Edition

Here Documents

A line-oriented form of quoting is based on the Unix shell “here-document” syntax. Following a <<, you specify a string to terminate the quoted material, and all lines following the current line down to the terminating string are the value of the item. This is of particular importance if you’re trying to print something like HTML that would be cleaner to print as a chunk instead of as individual lines. For example:

#!/usr/local/bin/perl -w

my $Price = 'right';
    
print <<"EOF";
The price is $Price.
EOF

The terminating string does not have to be quoted. For example, the previous example could have been written as:

#!/usr/local/bin/perl -w

my $Price = 'right';
    
print <<EOF;
The price is $Price.
EOF

You can assign here documents to a string:

my $assign_this_heredoc =<< "EOS";
This string is assigned to $whatever.
EOS

You can use a here document to execute commands:

#!/usr/local/bin/perl -w

print <<`CMD`;
ls -l
CMD

You can stack here documents:

#!/usr/local/bin/perl -w

print <<"joe", <<"momma"; # You can stack them
I said foo.
joe
I said bar.
momma

One caveat about here documents: you may have noticed in each of these examples that the quoted text is always left-justified. That’s because any whitespace used for indentation will be included in the string. For example:

#!/usr/local/bin/perl -w

print <<"    INDENTED";
    Same old, same old.
    INDENTED

Although you can use a trick of including whitespace in the terminating tag to keep it indented (as we did here), the string itself will have the ...