这被称为heredoc格式，用于向stdin提供字符串。详情见https://en.wikipedia.org/wiki/Here_document#Unix_shells。

来自man bash:

Here Documents This type of redirection instructs the shell to read input from the current source until a line containing only word (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, command substitution, and arithmetic expansion. In the latter case, the character sequence \<newline> 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.

长话短说，EOF标记(但也可以使用不同的文字)是一种heredoc格式，允许您以多行方式提供输入。 很多困惑来自于猫实际上是如何工作的。 你可以使用cat >>或>，如下所示:

$ cat >> temp.txt
line 1
line 2

虽然在手动写入控制台时可以这样使用cat，但如果我想以一种更声明性的方式提供输入，以便工具可以重用它，并保留缩进、空格等，则不方便。 Heredoc允许定义您的整个输入，就好像您不是在使用stdin，而是在单独的文本编辑器中输入一样。这是维基百科文章的意思:

它是源代码文件的一个部分，它被当作 单独的文件中。

这被称为heredoc格式，用于向stdin提供字符串。详情见https://en.wikipedia.org/wiki/Here_document#Unix_shells。

来自man bash:

Here Documents This type of redirection instructs the shell to read input from the current source until a line containing only word (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, command substitution, and arithmetic expansion. In the latter case, the character sequence \<newline> 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.

创建json文件的示例:

cat << EoF > ./allaccess.json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:*"
      ],
      "Resource": [
        "arn:aws:s3:::*"
      ]
    }
  ]
}
EoF

结果是:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:*"
      ],
      "Resource": [
        "arn:aws:s3:::*"
      ]
    }
  ]
}

值得注意的是，这里的文档也在bash循环中工作。 下面的例子展示了如何获取table的列列表:

export postgres_db_name='my_db'
export table_name='my_table_name'

# start copy 
while read -r c; do test -z "$c" || echo $table_name.$c , ; done < <(cat << EOF | psql -t -q -d $postgres_db_name -v table_name="${table_name:-}"
SELECT column_name
FROM information_schema.columns
WHERE 1=1
AND table_schema = 'public'
AND table_name   =:'table_name'  ;
EOF
)
# stop copy , now paste straight into the bash shell ...

output: 
my_table_name.guid ,
my_table_name.id ,
my_table_name.level ,
my_table_name.seq ,

或者甚至没有新的线条

while read -r c; do test -z "$c" || echo $table_name.$c , | perl -ne 
's/\n//gm;print' ; done < <(cat << EOF | psql -t -q -d $postgres_db_name -v table_name="${table_name:-}"
 SELECT column_name
 FROM information_schema.columns
 WHERE 1=1
 AND table_schema = 'public'
 AND table_name   =:'table_name'  ;
 EOF
 )

 # output: daily_issues.guid ,daily_issues.id ,daily_issues.level ,daily_issues.seq ,daily_issues.prio ,daily_issues.weight ,daily_issues.status ,daily_issues.category ,daily_issues.name ,daily_issues.description ,daily_issues.type ,daily_issues.owner

<< EoF的基本意思是:

<< - "读取从下一行开始的多行输入，并将其视为单独文件中的代码"

EoF -“在多行输入中发现单词EoF后立即停止阅读”

正如其他答案所解释的，多行输入称为Here文档

Here Document通常用于生成要传递给后续进程的输出。例如，cat << EoF可以使用Here Document生成所需的输出。

下面是一个使用Here Document动态创建文本文档的例子:

cat << EoF > ./my-document.txt
Hello world
Have a nice day
EoF