Bash Reference Manual
3.6.5 Here Documents
This type of redirection instructs the shell to read input from the
current source until a line containing only word
(with no trailing blanks) is seen. All of
the lines read up to that point are then used as the standard
input for a command.
The format of here-documents is:
No parameter expansion, command substitution, arithmetic expansion,
or filename expansion is performed on
word. If any characters in word are quoted, the
delimiter is the result of quote removal on word,
and the lines in the here-document are not expanded.
If word is unquoted,
all lines of the here-document are subjected to parameter expansion,
command substitution, and arithmetic expansion. In the latter
case, the character sequence
\newline is ignored, and `\'
must be used to quote the characters
`\', `$', and ``'.
If the redirection operator is `<<-',
then all leading tab characters are stripped from input lines and the
line containing delimiter.
This allows here-documents within shell scripts to be indented in a