8.18 Here Documents

So far, we've talked about three different kinds of quoting: backslashes ( \ ), single quotes ( ' ), and double quotes ( <"> ). The shells support yet one more kind of quoting, called here documents . A here document is useful when you need to read something from standard input, but you don't want to create a file to provide that input; you want to put that input right into your shell script (or type it directly on the command line). To do so, use the << operator, followed by a special word:

sort >file <<EndOfSort zygote abacus EndOfSort

This is very useful because variables ( 6.8 , 6.1 ) are evaluated during this operation. Here is a way to transfer a file using anonymous ftp ( 52.7 ) from a shell script:

#!/bin/sh # Usage: #     ftpfile machine file # set -x SOURCE=$1 FILE=$2 GETHOST="uname -n" BFILE=`basename $FILE` ftp -n $SOURCE <<EndFTP ascii user anonymous $USER@`$GETHOST` get $FILE /tmp/$BFILE EndFTP

As you can see, variables and command substitutions ( 9.16 ) are done. If you don't want those to be done, put a backslash in front of the name of the word:

cat >file <<\FunkyStriNG

Notice the funky string. This is done because it is very unlikely that I will want to put that particular combination of characters in any file. You should be warned that the C shell expects the matching word (at the end of the list) to be escaped the same way, i.e., \FunkyStriNG , while the Bourne shell does not. See article 45.26 .

[Most Bourne shells also have the <<- operator. The dash ( - ) at the end tells the shell to strip any TAB characters from the beginning of each line. Use this in shell scripts to indent a section of text without passing those TABs to the command's standard input. -JP ]