mirror of
https://github.com/LCTT/TranslateProject.git
synced 2024-12-26 21:30:55 +08:00
213 lines
4.3 KiB
Markdown
213 lines
4.3 KiB
Markdown
Bash 脚本中如何使用 here 文档将数据写入文件
|
||
======
|
||
|
||
<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][1]
|
||
|
||
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][3]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][3]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][a]
|
||
译者：[Flowsnow](https://github.com/Flowsnow)
|
||
校对：[wxy](https://github.com/wxy)
|
||
|
||
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
|
||
|
||
[a]: https://www.cyberciti.biz
|
||
[1]: https://www.cyberciti.biz/media/new/faq/2017/11/redirect-output-of-here-document-to-a-text-file.jpg
|
||
[2]: https://bash.cyberciti.biz/guide/Here_documents
|
||
[3]: https//www.cyberciti.biz/faq/linux-unix-appleosx-bsd-cat-command-examples/
|