SHELL中打印字符时用echo, 当打印N多行字符时，显然ECHO有点吃力。这时候就需要EOF上场了。

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cat <<"EOF"
 /$$   /$$           /$$ /$$                 /$$$$$$$$  /$$$$$$  /$$$$$$$$
| $$  | $$          | $$| $$                | $$_____/ /$$__  $$| $$_____/
| $$  | $$  /$$$$$$ | $$| $$  /$$$$$$       | $$      | $$  \ $$| $$      
| $$$$$$$$ /$$__  $$| $$| $$ /$$__  $$      | $$$$$   | $$  | $$| $$$$$   
| $$__  $$| $$$$$$$$| $$| $$| $$  \ $$      | $$__/   | $$  | $$| $$__/   
| $$  | $$| $$_____/| $$| $$| $$  | $$      | $$      | $$  | $$| $$      
| $$  | $$|  $$$$$$$| $$| $$|  $$$$$$/      | $$$$$$$$|  $$$$$$/| $$      
|__/  |__/ \_______/|__/|__/ \______/       |________/ \______/ |__/      
EOF

Here Document

　　专业术语Here Document,是一种特殊的IO重定向，EOF=End of File.

  1. EOF作为分隔符代号，可以写成任意字符，只需要保证前后一样即可.

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    cat <<abcdefo
Any char is
OK!
abcdefo

  2. 当不需要转义，即想输出变量值是。去掉双引号。 下面输出echo HELLO WORLD

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    VAR="HELLO WORLD"
cat <<var
echo ${VAR}
var

  3. 高级用法可以输出template文件。这们可以输出文件到template.txt。

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    NAME=wxdlong
AGE=18
cat <<template>template.txt
Hello ${NAME}
Your age is ${AGE}
template

  4. 定义带换行的变量值。 echo "${variable}"试试看输出？

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    variable=$(cat <<SETVAR
This variable
runs over multiple lines.
SETVAR
)

  5. 当注释用.

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    : <<COMMENTBLOCK
echo "This line will not echo."
This is a comment line missing the "#" prefix.
This is another comment line missing the "#" prefix.

&*@!!++=
The above line will cause no error message,
because the Bash interpreter will ignore it.
COMMENTBLOCK

  6. 替换交互输入。