Here documents

The final concept we'll introduce in this chapter is the here document. Here documents, also called heredocs, are used to supply input to certain commands, slightly different to stdin redirection. Notably, it is an easy way to give multiline input to a command. It works with the following syntax:

cat << EOF
input
more input
the last input
EOF

If you run this in your Terminal, you'll see the following:

reader@ubuntu:~/scripts/chapter_12$ cat << EOF
> input
> more input
> the last input
> EOF
input
more input
the last input

The << syntax lets Bash know you want to use a heredoc. Right after that, you're supplying a delimiting identifier. This might seem complicated, but it really means that you supply a string that will terminate the input. So, in our example, we supplied the commonly used EOF (short for end of file).

Now, if the heredoc encounters a line in the input that exactly matches the delimiting identifier, it stops listening for further input...