>> [root@localhost learn_sed]# /bin/sed "s/\'/ End/" tmp.txt
>> hello world End
>> I'am in china End
>> [root@localhost learn_sed]#
>> ### My Question
>> I want to know the reason.  \' be equal to Line End ?

> Thanks for the report.  However, this is not a bug, but a GNU extension,
> as documented here:
> https://www.gnu.org/software/sed/manual/html_node/Escapes.html#Escapes

> In your particular case, end of line and end of input happen to match.
> But if your sed script had also used commands like 'N', then you could
> see a difference where multi-line mode makes \' match fewer places than $.