From the ksh man page:
<<[-]word The shell input is read up to a line that matches word, or to an end-of-file. No parameter
substitution, command substitution, or file name generation is performed on word. The resulting
document, called a here-document, becomes the standard input. If any character of word is quoted,
no interpretation is placed upon the characters of the document. Otherwise, parameter and command
substitution occurs, \new-line is ignored, and \ must be used to quote the characters \, $, `, and
the first character of word. If - is appended to <<, all leading tabs are stripped from word and
from the document.
Also, take a look at: changepass automate password changes on multiple systems