Summary: How to use Perl here documents, i.e., the Perl heredoc syntax.
Perl offers a convenient way of printing multiple lines of output through an interesting feature known as a "Perl here document". A here document, or heredoc, lets you easily store multiple lines of text in a Perl variable.
A multiline Perl here document works like this:
- The first line of your command will include the two characters
<<followed by a "special" identifier string, followed by a semi-colon. (For my example I will use the identifier string
FOO. More on this shortly.)
- Next, just enter all of the lines of output that you want to print.
- When you are ready to terminate the output, put your special identifier string on a line by itself to end the output.
A Perl here document example
Confused? Probably. Here's an example of how to use this. Imagine you wanted to print a few lines from the Gettysburg address from inside of a Perl program:
print <<FOO; Four score and seven years ago our fathers set onto this continent (keep going here ...) FOO
If you put this in a Perl program, and then run the program, this will print the lines in between "
print <<FOO;" and "
FOO", so you will see this output:
Four score and seven years ago our fathers set onto this continent (keep going here ...)
I don't know the history, so I can't tell you why they're called "here" documents, but I can tell you that it makes it easy to print multiple lines of output from a Perl program.
Perl here documents (heredoc) - Summary
I hope these Perl heredoc examples have been helpful. As you can see, the Perl heredoc syntax lets you easily store multiple lines of text in a Perl variable, and when you think about the alternative syntax required to achieve something like this, you realize how incredibly useful the Perl here document syntax is.