Here is a linguistic construct that originated in the Unix shell. It is a document literal that originates in the Unix shell, although similar facilities exist in other languages. In the context of programming, here means “this document” or “this file.”
The term “here” is used for documents with multiple lines of text. It is also used to refer to a single line of text, but it has different meanings in different languages. A here document is a multiline string Here. In Unix shells, you can pass the text in the form of a shell file or type it interactively at a prompt. The old way to use here documents was to specify the beginning and ending of the document with END. This means that you don’t need to use a space between the delimiting identifier and the redirection.
There are several ways to invoke here docs. Inline double quotes and single quotes have the same effect as a normal string literal. Single quotes do not enclose the tag. If you want to use double quotes, add them around the heredoc tag. Using double quotes is more common than using single quotes. Using backticks around the heredoc tag will run the contents of the file like a shell script.