1.here文档
here文档允许我们调用一个交互式程序；可以从脚本程序中输出大量的文本，从而不必echo每行
例子1：
#!/bin/bash
cat<<!DATA!
This is a simple use of the here document.This data is the
input given to the above cat command
!DATA
其输出为：
This is a simple use of the here document.This data is the
input given to the above cat command
例子2（与grep搜索命令的交互）：
demo_dext 文件内容
#!/bin/bash
if [ $# -eq 0]
then
echo "Usage:$0 name"
exit 1
fi
user_input="$1"
grep -i $user_input<<!DIRECTORY!
John Doe 1234567 hahahah
David Nice 3248428 jjkjkll
Don Carr 8989897 jkdjasl
!DIRECTORY!
exit 0
执行：
$chmod u+x demo_dext
$./demo_dext John
John Doe 1234567 hahahah