Grep: Combining -o and -v flags does not work

Question

我想结合grep 的-o和-v标志。但我没有得到任何输出。我有文件：

foo
bar
foobar

我打电话：grep -vo foo ./file

我期望什么：

bar
bar

或者

bar
bar

但我没有得到任何输出。

从 grep 的手册页中：

   -o, --only-matching
          Print only the matched (non-empty) parts of a matching line, with each such part on a separate output line.
...
   -v, --invert-match
          Invert the sense of matching, to select non-matching lines.

当我只使用一个标志时，行为正如我所期望的那样。但是如何让 grep 与两个标志同时工作呢？我在 Debian AMD64 上使用 grep (GNU grep) 3.3。

Answer 1

你要说的grep是：

• 仅打印foo包含它的每一行，并且
• Print lines that don't have a foo

What you meant to tell grep was:

• Print lines that don't match foo, or the parts of lines that don't include a foo

That can be reduced to:

• Print every line, but remove foo from them

I think sed is the perfect tool to do this:

$ sed 's/foo//g' ./file

bar
bar

This says: for each line, substitute foo with nothing globally. By globally it means every instance in the line.

If you also want to delete empty lines:

$ sed -e 's/foo//g' -e '/^$/d' ./file
bar
bar

This says:

• substitute foo with nothing globally, then
• for each empty line, delete it