Here Document Example #1: Unformatted Form Letters (Unix Power Tools, 3rd Edition)

28.13. Here Document Example #1: Unformatted Form Letters

<<Section 27.16

The here document operator << (Section 27.16) is often used in shell scripts -- but it's also handy at a shell prompt, especially with zsh multiline editing or a throwaway script. But you also can just type it in at a Bourne shell prompt (Section 28.12). (If you use csh or tcsh, you can either use a foreach loop (Section 28.9) or start a subshell (Section 24.4).)

The example below shows a for loop (Section 28.9) that prints three friendly form letters with the lpr (Section 45.2) command. Each letter has a different person's name and the current date at the top. Each line of the loop body starts with a TAB character, which the <<- operator removes before the printer gets the text:

for person in "Mary Smith" "Doug Jones" "Alison Eddy"
do
   lpr <<- ENDMSG

   `date`

   Dear $person,

   This is your last notice. Buy me pizza tonight or
   else I'll type "rm -r *" when you're not looking.

   This is not a joak.

   Signed,
   The midnight skulker
   ENDMSG
done

The shell reads the standard input until it finds the terminator word, which in this case is ENDMSG. The word ENDMSG has to be on a line all by itself. (Some Bourne shells don't have the <<- operator to remove leading TAB characters. In that case, use << and don't indent the loop body.) The backquotes (Section 28.14) run the date command and output its date; $person is replaced with the person's name set at the top of the loop. The rest of the text is copied as is to the standard input of the lpr command.

-- JP