如何在命令中使用文件并将输出重定向到同一个文件而不截断它? [英] How can I use a file in a command and redirect output to the same file without truncating it?

问题描述

基本上我想从文件中获取输入文本，从该文件中删除一行，然后将输出发送回同一个文件.如果这能让事情更清楚的话，应该遵循这些原则.

Basically I want to take as input text from a file, remove a line from that file, and send the output back to the same file. Something along these lines if that makes it any clearer.

grep -v 'seg[0-9]{1,}.[0-9]{1}' file_name > file_name

但是，当我这样做时，我最终得到了一个空白文件.有什么想法吗?

however, when I do this I end up with a blank file. Any thoughts?

推荐答案

你不能这样做，因为 bash 首先处理重定向，然后执行命令.所以当 grep 查看 file_name 时，它​​已经是空的.不过，您可以使用临时文件.

You cannot do that because bash processes the redirections first, then executes the command. So by the time grep looks at file_name, it is already empty. You can use a temporary file though.

#!/bin/sh
tmpfile=$(mktemp)
grep -v 'seg[0-9]{1,}.[0-9]{1}' file_name > ${tmpfile}
cat ${tmpfile} > file_name
rm -f ${tmpfile}

像那样，考虑使用 mktemp 来创建 tmpfile 但请注意它不是 POSIX.

like that, consider using mktemp to create the tmpfile but note that it's not POSIX.

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