如何从 shell 在 Linux 中将一个文件附加到另一个文件？

How to append one file to another in Linux from the shell?

提问by asir

I have two files: file1and file2. How do I append the contents of file2to file1so that contents of file1persist the process?

我有两个文件：file1和file2. 我如何附加file2to的内容以file1使file1该过程的内容持久化？

回答by David

Use bash builtin redirection (tldp):

使用bash 内置重定向（tldp）：

cat file2 >> file1

回答by eumiro

Try this command:

试试这个命令：

cat file2 >> file1

回答by T.Rob

cat file2 >> file1

cat file2 >> file1

The >>operator appends the output to the named file or creates the named file if it does not exist.

该>>运营商将输出追加到指定的文件或创建命名的文件，如果它不存在。

cat file1 file2 > file3

cat file1 file2 > file3

This concatenates two or more files to one. You can have as many source files as you need. For example,

这将两个或多个文件连接为一个。您可以根据需要拥有任意数量的源文件。例如，

cat *.txt >> newfile.txt

cat *.txt >> newfile.txt

Update 20130902
In the comments eumiro suggests "don't try cat file1 file2 > file1." The reason this might not result in the expected outcome is that the file receiving the redirect is prepared before the command to the left of the >is executed. In this case, first file1is truncated to zero length and opened for output, then the catcommand attempts to concatenate the now zero-length file plus the contents of file2into file1. The result is that the original contents of file1are lost and in its place is a copy of file2which probably isn't what was expected.

更新 20130902
在评论中 eumiro 建议“不要尝试” cat file1 file2 > file1。这可能不会导致预期结果的原因是接收重定向的文件是在>执行左侧的命令之前准备好的。在这种情况下，首先file1被截断为零长度并打开输出，然后cat命令尝试连接现在为零长度的文件加上file2into的内容file1。结果是 的原始内容file1丢失了，取而代之的是file2可能不是预期的副本。

Update 20160919
In the comments tpartee suggests linking to backing information/sources. For an authoritative reference, I direct the kind reader to the sh man pageat linuxcommand.org which states:

更新 20160919
在评论中 tpartee 建议链接到支持信息/来源。为了获得权威参考，我将好心的读者引导至linuxcommand.org上的sh 手册页，其中指出：

Before a command is executed, its input and output may be redirected using a special notation interpreted by the shell.

在执行命令之前，可以使用由 shell 解释的特殊符号重定向其输入和输出。

While that does tell the reader what they need to know it is easy to miss if you aren't looking for it and parsing the statement word by word. The most important word here being 'before'. The redirection is completed (or fails) beforethe command is executed.

虽然这确实告诉读者他们需要知道什么，但如果您不寻找它并逐字解析语句，则很容易错过。这里最重要的词是“之前”。重定向在命令执行之前完成（或失败）。

In the example case of cat file1 file2 > file1the shell performs the redirection first so that the I/O handles are in place in the environment in which the command will be executed before it is executed.

在cat file1 file2 > file1shell的示例情况下，首先执行重定向，以便 I/O 句柄在执行命令之前在命令执行的环境中就位。

A friendlier version in which the redirection precedence is covered at length can be found at Ian Allen's web site in the form of Linux courseware. His I/O Redirection Notespage has much to say on the topic, including the observation that redirection works even without a command. Passing this to the shell:

可以在 Ian Allen 的网站上以 Linux 课件的形式找到一个更友好的版本，其中详细介绍了重定向优先级。他的I/O Redirection Notes页面对这个主题有很多话要说，包括观察到重定向即使没有命令也能工作。将此传递给外壳：

$ >out

...creates an empty file named out. The shell first sets up the I/O redirection, then looks for a command, finds none, and completes the operation.

...创建一个名为 out 的空文件。shell首先设置I/O重定向，然后查找命令，没有找到，完成操作。

回答by Zorawar

Just for reference, using ddrescue provides an interruptible way of achieving the task if, for example, you have large files and the need to pause and then carry on at some later point:

仅供参考，使用 ddrescue 提供了一种可中断的方式来完成任务，例如，如果您有大文件并且需要暂停然后在稍后继续执行：

ddrescue -o $(wc --bytes file1 | awk '{ print  }') file2 file1 logfile

The logfileis the important bit. You can interrupt the process with Ctrl-Cand resume it by specifying the exact same command again and ddrescue will read logfileand resume from where it left off. The -o Aflag tells ddrescue to start from byte Ain the output file (file1). So wc --bytes file1 | awk '{ print $1 }'just extracts the size of file1in bytes (you can just paste in the output from lsif you like).

这logfile是重要的一点。您可以Ctrl-C通过再次指定完全相同的命令来中断进程并恢复它，ddrescue 将从logfile它停止的地方读取和恢复。该-o A标志告诉 ddrescue 从输出文件 ( )中的字节A开始file1。所以wc --bytes file1 | awk '{ print $1 }'只需提取file1以字节为单位的大小（ls如果你愿意，你可以粘贴输出）。

As pointed out by ngksin the comments, the downside is that ddrescue will probably not be installed by default, so you will have to install it manually. The other complication is that there are two versions of ddrescue which might be in your repositories: see this askubuntu questionfor more info. The version you want is the GNU ddrescue, and on Debian-based systems is the package named gddrescue:

正如ngks在评论中指出的那样，缺点是默认情况下可能不会安装 ddrescue，因此您必须手动安装它。另一个复杂问题是您的存储库中可能有两个版本的 ddrescue：有关更多信息，请参阅此 askubuntu 问题。你想要的版本是 GNU ddrescue，在基于 Debian 的系统上是名为 的包gddrescue：

sudo apt install gddrescue

For other distros check your package management system for the GNUversion of ddrescue.

对于其他发行版，请检查您的包管理系统以获取ddrescue的GNU版本。

回答by jdunk

Note: if you need to use sudo, do this:

注意：如果您需要使用sudo，请执行以下操作：

sudo bash -c 'cat file2 >> file1'

sudo bash -c 'cat file2 >> file1'

The usual method of simply prepending sudoto the command will fail, since the privilege escalation doesn't carry over into the output redirection.

简单地添加sudo到命令前面的常用方法将失败，因为权限提升不会延续到输出重定向中。

回答by Amey Jadiye

catcan be the easy solution but that become very slow when we concat large files, find -printis to rescue you, though you have to use cat once.

cat可能是一个简单的解决方案，但是当我们连接大文件时会变得非常慢，这find -print是为了拯救你，尽管你必须使用 cat 一次。

amey@xps ~/work/python/tmp $ ls -lhtr
total 969M
-rw-r--r-- 1 amey amey 485M May 24 23:54 bigFile2.txt
-rw-r--r-- 1 amey amey 485M May 24 23:55 bigFile1.txt

 amey@xps ~/work/python/tmp $ time cat bigFile1.txt bigFile2.txt >> out.txt

real    0m3.084s
user    0m0.012s
sys     0m2.308s


amey@xps ~/work/python/tmp $ time find . -maxdepth 1 -type f -name 'bigFile*' -print0 | xargs -0 cat -- > outFile1

real    0m2.516s
user    0m0.028s
sys     0m2.204s

回答by Stefan van den Akker

Another solution:

另一种解决方案：

cat file1 | tee -a file2

teehas the benefit that you can append to as many files as you like, for example:

tee具有可以附加到任意数量的文件的好处，例如：

cat file1 | tee -a file2 file3 file3

will append the contents of file1to file2, file3and file4.

将附加file1到file2,file3和的内容file4。

From the man page:

从手册页：

-a, --append
       append to the given FILEs, do not overwrite

回答by Alok Singh

You can also do this without cat, though honestly catis more readable:

您也可以在没有 的情况下执行此操作cat，但老实说cat更具可读性：

>> file1 < file2

>> file1 < file2

The >>appends STDINto file1and the <dumps file2to STDIN.

该>>附加标准输入到file1和<转储file2到STDIN。