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.

对上面的答案做一点扩展。后面的>将输入引导到文件中，覆盖现有内容。然而，一个特别方便的用法是双箭头>>追加，将您的新内容添加到文件的末尾，如:

cat <<EOF >> /etc/fstab
data_server:/var/sharedServer/authority/cert /var/sharedFolder/sometin/authority/cert nfs
data_server:/var/sharedServer/cert   /var/sharedFolder/sometin/vsdc/cert nfs
EOF

这将扩展fstab，而不必担心意外修改其中的任何内容。

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。

在Bash中处理多行文本时，cat <<EOF语法非常有用。当将多行字符串分配给shell变量、文件或管道时。

在Bash中使用cat <<EOF语法的例子:

1. 为shell变量分配多行字符串

$ sql=$(cat <<EOF
SELECT foo, bar FROM db
WHERE foo='baz'
EOF
)

$sql变量现在也保存换行字符。你可以用echo -e "$sql"来验证。

2. 在Bash中传递多行字符串到文件

$ cat <<EOF > print.sh
#!/bin/bash
echo \$PWD
echo $PWD
EOF

print.sh文件现在包含:

#!/bin/bash
echo $PWD
echo /home/user

3.在Bash中将多行字符串传递给管道

$ cat <<EOF | grep 'b' | tee b.txt
foo
bar
baz
EOF

b.txt文件包含bar和baz行。相同的输出被打印到stdout。

这并不一定是对最初问题的回答，而是分享我自己测试的一些结果。这样的:

<<test > print.sh
#!/bin/bash
echo \$PWD
echo $PWD
test

将生成与以下相同的文件:

cat <<test > print.sh
#!/bin/bash
echo \$PWD
echo $PWD
test

所以，我不明白使用cat命令的意义。