regex - 正则表达式问题

Question

可能这是新手问题，但我必须问!
一般来说，我理解正则表达式，但我不明白，为什么这个:

^.{8}[[:blank:]]{2}

在这条线上工作:

prelink: /lib/libkeyutils-1.2.so: at least one of file's dependencies has changed since prelinking

在这个 grep 命令中:

echo "prelink: /lib/libkeyutils-1.2.so: at least one of file's dependencies has changed since prelinking" | grep -v '^.\{8\}[[:blank:]]\{2\}'

哪里:

The                says "beggining of line"  
The .{8}           says "any eight characters"  
The [[:blank:]]{2} says "any two space characters"  

So ^.{8} match "prelink:", when [[:blank:]]{2} need matching "  " (two spaces), but we have only " " (one space)... So why this work at all, and if this work why this one:

^.{8}[[:blank:]]{1} 

不起作用？

谢谢你提前。

Answer 1

您正在使用 grep 和 -v 选项，这导致它打印不匹配的行。删除 -v，它将按您预期的那样工作。

grep --help
...
   -v, --invert-match        select non-matching lines
...