我如何使用bash的“<<”运算符？

我知道bash有一个>>运算符，可以将输出附加到文件中，但是<<运算符的用途是什么？

Answer 1

使用

 info bash 

然后搜索（键入’/’后跟’<<'）。
这是部分报价：

 Here Documents This type of redirection instructs the shell to read input from the current source until a line containing only delimiter (with no trailing blanks) is seen. All of the lines read up to that point are then used as the standard input for a command. The format of here-documents is: <<[-]word here-document delimiter No parameter expansion, command substitution, arithmetic expansion, or pathname expansion is performed on word. If any characters in word are quoted, the delimiter is the result of quote removal on word, and the lines in the here-document are not expanded. If word is unquoted, all lines of the here-document are subjected to parameter expansion, com‐ mand substitution, and arithmetic expansion. In the latter case, the character sequence \ is ignored, and \ must be used to quote the characters \, $, and `. If the redirection operator is <<-, then all leading tab characters are stripped from input lines and the line containing delimiter. This allows here-documents within shell scripts to be indented in a natural fashion. Here Strings A variant of here documents, the format is: << 

Answer 2

 $ cat < This is a test > EOF This is a test $