[Chapter 9] 9.14 Using Here Documents for Form Letters, etc.
Author: Jerry Peek, Tim O'Reilly & Mike Loukides
Date: 1998-08-04T21:35:08Z

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| Chapter 9 Saving Time on the Command Line |

## 9.14 Using Here Documents for Form Letters, etc.

The here document operator `<<` (8.18) is used in shell scripts. It tells the shell to take lines from the script as standard input to a command. The example below shows a loop (45.17) that prints three nasty form letters with the lpr (43.2) command. Each letter has a different person's name and the current date at the top. You can put this loop into a shell script (44.2) or just type it in at a Bourne shell prompt (9.12, 9.13). 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

Warning! | This loop runs three lpr commands; each form letter prints on a separate page. 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 (9.16) run the date (51.10) 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

9.13 Multiline Commands, Secondary Prompts |  | 9.15 Throwaway Scripts for Complicated Commands