Linux Shell Here Document

Here Document code block there is a special use, and he uses the redirection IO recorded in the form of text or some temporary interaction commands, and these text or commands are sequentially transmitted to a program or a command, as his runtime standard input.

Here document syntax is

void@void-ThinkPad-E450:~/linuxShellArg$ command << delimiter
> document
> docuemnt
> document
> delimiter

<< bash as the operator inputs an instruction, the latter is an identifier of the start and end delimiter identifier, the output will always bash> prompt, the user waits for input data, up to the second user input until the delimiter identifier he indicates that the input end. Delimiter between two data will be used as a standard command command input.

Delimiter identifier may be any string, but only a word delimiter, intervening spaces or Tab.

Here document often used to help function o Shell scripts, for example, the android build / envsetup.sh

function hmm() {
cat <<EOF
Invoke ". build/envsetup.sh" from your shell to add the following functions to your environment:
- lunch:   lunch <product_name>-<build_variant>
- tapas:   tapas [<App1> <App2> ...] [arm|x86|mips|armv5] [eng|userdebug|user]
- croot:   Changes directory to the top of the tree.
- m:       Makes from the top of the tree.
- mm:      Builds all of the modules in the current directory, but not their dependencies.
- mmm:     Builds all of the modules in the supplied directories, but not their dependencies.
- mma:     Builds all of the modules in the current directory, and their dependencies.
- mmma:    Builds all of the modules in the supplied directories, and their dependencies.
- cgrep:   Greps on all local C/C++ files.
- jgrep:   Greps on all local Java files.
- resgrep: Greps on all local res/*.xml files.
- godir:   Go to the directory containing a file.

Look at the source to view more functions. The complete list is:
EOF
    T=$(gettop)
    local A
    A=""
    for i in `cat $T/build/envsetup.sh | sed -n "/^function /s/function \([a-z_]*\).*/\1/p" | sort`; do
      A="$A $i"
    done
    echo  $A
}

In the HMM function () is shown here document some help information, here document where the output to the screen by the cat command, and uses the delimiter identifier EOF.