如何在不删除文件的情况下重定向cat myfile>我的档案 [英] How to redirect without erasing file cat myfile > myfile

问题描述

我对不删除文件重定向到文件的正确方法有疑问? 我正在使用bash.我想做类似的事情:

I have a question about what is the right way to redirect to a file without erasing the file? I'm using bash. I would like to do something like:

cat myfile > myfile

程序(即cat)读取文件然后重定向到文件的位置，因此在上面的示例中，"myfile"将保持不变.

where the program (i.e. cat) reads the file and then redirects to the file, so in the example above 'myfile' would be unchanged.

我知道上面的示例将删除文件在这里解释.

I know that the example above will erase the file, as explained here.

什么是正确的语法，这样就不会删除文件?是否可以进行stdout和重定向，或者程序应处理打开新数据并将新数据写入文件的操作?我想让我的程序只输出到stdout，然后用户可以重定向或管道或其他任何内容.

What is the proper syntax so the file won't be erased? Is stdout and redirection possible, or should the program handle opening and writing the new data to the file? I would like to let my program just output to stdout and then the user can redirect or pipe or whatever.

顺便说一句，我不想​​>>和连接.我希望左侧的函数将新"数据写入文件.

BTW, I don't want to >> and concatenate. I want the function on the left to write "new" data to the file.

也许更好的说法是，我希望重定向的左侧在流式传输发生之前完全发生，这可能吗?如果我对bash有基本的误解，请告诉我:-)

Perhaps a better way to state it is that I want the left side of the redirection to fully occur before the streaming occurs, is this possible? If I have a fundamental misunderstanding of bash here, please enlighten me :-)

推荐答案

您必须先将所有数据读取到内存中，或者写入一个临时文件并将其换出.

You have to either read all the data to memory first, or write to a temporary file and swap it out.

要将其读入内存(如vim，ed和其他编辑器一样):

To read it into memory (like vim, ed and other editors do):

contents=$(<myfile)
cat <<< "$contents" > myfile

要创建一个临时文件(例如sed -i，rsync和其他更新工具):

To create a temporary file (like sed -i, rsync and other updating tools do):

tmpfile=$(mktemp fooXXXXXX)
cat myfile > "$tmpfile" && mv "$tmpfile" myfile

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