---
author: Vivek Gite
category: 技术
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date: '2018-11-12 09:51:20'
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excerpt: here 文档不是什么特殊的东西，只是一种 I/O 重定向方式，它告诉 bash shell 从当前源读取输入，直到读取到只有分隔符的行。
fromurl: https://www.cyberciti.biz/faq/using-heredoc-rediection-in-bash-shell-script-to-write-to-file/
id: 10224
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summary: here 文档不是什么特殊的东西，只是一种 I/O 重定向方式，它告诉 bash shell 从当前源读取输入，直到读取到只有分隔符的行。
tags:
- here
- bash
thumb: false
title: Bash 脚本中如何使用 here 文档将数据写入文件
titlepic: true
translator: Flowsnow
updated: '2018-11-12 09:51:20'
---

<ruby> here 文档 <rt>  here document </rt></ruby> （LCTT 译注：here 文档又称作 heredoc ）不是什么特殊的东西，只是一种 I/O 重定向方式，它告诉 bash shell 从当前源读取输入，直到读取到只有分隔符的行。


![redirect output of here document to a text file](/images/p/201811/12/095122pd5k2kwhkkj22k2s.jpg)


这对于向 ftp、cat、echo、ssh 和许多其他有用的 Linux/Unix 命令提供指令很有用。 此功能适用于 bash 也适用于 Bourne、Korn、POSIX 这三种 shell。


### here 文档语法


语法是：



```
command <<EOF
cmd1
cmd2 arg1
EOF
```

或者允许 shell 脚本中的 here 文档使用 `EOF<<-` 以自然的方式缩进：



```
command <<-EOF
  msg1
  msg2 
  $var on line 
EOF
```

或者



```
command <<'EOF'
 cmd1
 cmd2 arg1
 $var won't expand as parameter substitution turned off
 by single quoting
EOF
```

或者 **重定向并将其覆盖** 到名为 `my_output_file.txt` 的文件中：



```
command <<EOF > my_output_file.txt
 mesg1
 msg2
 msg3
 $var on $foo
EOF
```

或**重定向并将其追加**到名为 `my_output_file.txt` 的文件中：



```
command <<EOF >> my_output_file.txt
 mesg1
 msg2
 msg3
 $var on $foo
EOF
```

### 示例


以下脚本将所需内容写入名为 `/tmp/output.txt` 的文件中：



```
#!/bin/bash
OUT=/tmp/output.txt

echo "Starting my script..."
echo "Doing something..."

cat <<EOF >$OUT
  Status of backup as on $(date)
  Backing up files $HOME and /etc/
EOF

echo "Starting backup using rsync..."
```

你可以使用[cat命令](https//www.cyberciti.biz/faq/linux-unix-appleosx-bsd-cat-command-examples/)查看/tmp/output.txt文件：



```
$ cat /tmp/output.txt
```

示例输出：



```
 Status of backup as on Thu Nov 16 17:00:21 IST 2017
 Backing up files /home/vivek and /etc/
```

### 禁用路径名/参数/变量扩展、命令替换、算术扩展


像 `$HOME` 这类变量和像 `$(date)` 这类命令在脚本中会被解释为替换。 要禁用它，请使用带有 `'EOF'` 这样带有单引号的形式，如下所示：



```
#!/bin/bash
OUT=/tmp/output.txt

echo "Starting my script..."
echo "Doing something..."
# No parameter and variable expansion, command substitution, arithmetic expansion, or pathname expansion is performed on word.  
# If any part of word is quoted, the delimiter  is  the  result  of  quote removal  on word, and the lines in the here-document 
# are not expanded. So EOF is quoted as follows
cat <<'EOF' >$OUT
  Status of backup as on $(date)
  Backing up files $HOME and /etc/
EOF

echo "Starting backup using rsync..."
```

你可以使用 [cat 命令](https//www.cyberciti.biz/faq/linux-unix-appleosx-bsd-cat-command-examples/)查看 `/tmp/output.txt` 文件：



```
$ cat /tmp/output.txt
```

示例输出：



```
 Status of backup as on $(date)
 Backing up files $HOME and /etc/

```

### 关于 tee 命令的使用


语法是：



```
tee /tmp/filename <<EOF >/dev/null
line 1
line 2
line 3
$(cmd)
$var on $foo
EOF
```

或者通过在单引号中引用 `EOF` 来禁用变量替换和命令替换：



```
tee /tmp/filename <<'EOF' >/dev/null
line 1
line 2
line 3
$(cmd)
$var on $foo
EOF
```

这是我更新的脚本：



```
#!/bin/bash
OUT=/tmp/output.txt

echo "Starting my script..."
echo "Doing something..."

tee $OUT <<EOF >/dev/null
  Status of backup as on $(date)
  Backing up files $HOME and /etc/
EOF

echo "Starting backup using rsync..."
```

### 关于内存 here 文档的使用


这是我更新的脚本：



```
#!/bin/bash
OUT=/tmp/output.txt

## in memory here docs 
## thanks https://twitter.com/freebsdfrau
exec 9<<EOF
  Status of backup as on $(date)
  Backing up files $HOME and /etc/
EOF

## continue
echo "Starting my script..."
echo "Doing something..."

## do it
cat <&9 >$OUT

echo "Starting backup using rsync..."
```



---


via: <https://www.cyberciti.biz/faq/using-heredoc-rediection-in-bash-shell-script-to-write-to-file/>


作者：[Vivek Gite](https://www.cyberciti.biz) 译者：[Flowsnow](https://github.com/Flowsnow) 校对：[wxy](https://github.com/wxy)


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