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。

POSIX 7

kennytm引用了man bash，但其中大部分也是POSIX 7: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_07_04:

The redirection operators "<<" and "<<-" both allow redirection of lines contained in a shell input file, known as a "here-document", to the input of a command. The here-document shall be treated as a single word that begins after the next <newline> and continues until there is a line containing only the delimiter and a <newline>, with no <blank> characters in between. Then the next here-document starts, if there is one. The format is as follows: [n]<<word here-document delimiter where the optional n represents the file descriptor number. If the number is omitted, the here-document refers to standard input (file descriptor 0). If any character in word is quoted, the delimiter shall be formed by performing quote removal on word, and the here-document lines shall not be expanded. Otherwise, the delimiter shall be the word itself. If no characters in word are quoted, all lines of the here-document shall be expanded for parameter expansion, command substitution, and arithmetic expansion. In this case, the <backslash> in the input behaves as the <backslash> inside double-quotes (see Double-Quotes). However, the double-quote character ( '"' ) shall not be treated specially within a here-document, except when the double-quote appears within "$()", "``", or "${}". If the redirection symbol is "<<-", all leading <tab> characters shall be stripped from input lines and the line containing the trailing delimiter. If more than one "<<" or "<<-" operator is specified on a line, the here-document associated with the first operator shall be supplied first by the application and shall be read first by the shell. When a here-document is read from a terminal device and the shell is interactive, it shall write the contents of the variable PS2, processed as described in Shell Variables, to standard error before reading each line of input until the delimiter has been recognized.

例子

有些例子还没有给出。

引号阻止参数扩展

没有引用:

a=0
cat <<EOF
$a
EOF

输出:

0

报价:

a=0
cat <<'EOF'
$a
EOF

或者(丑陋但有效):

a=0
cat <<E"O"F
$a
EOF

输出:

$a

连字符删除开头制表符

没有连字符:

cat <<EOF
<tab>a
EOF

其中<tab>是一个文字制表符，可以用Ctrl + V <tab>

输出:

<tab>a

用连字符:

cat <<-EOF
<tab>a
<tab>EOF

输出:

a

当然，这是为了让您可以像周围的代码一样缩进您的cat，这更容易阅读和维护。例如:

if true; then
    cat <<-EOF
    a
    EOF
fi

不幸的是，这并不适用于空格字符:POSIX偏爱制表符缩进。呵。

在你的例子中，“EOF”被称为“Here Tag”。基本上，<<Here告诉shell，您将输入一个多行字符串，直到“tag”在这里。你可以随意命名这个标签，通常是EOF或STOP。

关于Here标签的一些规则:

标签可以是任何字符串，大写或小写，尽管大多数人习惯使用大写。 如果该行中有其他单词，则该标记将不被视为Here标记。在这种情况下，它仅仅被认为是字符串的一部分。标签本身应该在单独的行中，被认为是一个标签。 标签在该行中不应该有前导或尾随空格，才能被视为标签。否则它将被视为字符串的一部分。

例子:

$ cat >> test <<HERE
> Hello world HERE <-- Not by itself on a separate line -> not considered end of string
> This is a test
>  HERE <-- Leading space, so not considered end of string
> and a new line
> HERE <-- Now we have the end of the string

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。

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