Remove characters before the last underscore and replace them with a numerical value

Question

[Percy]

How do I edit and remove similar characters from a fasta file headers before the last underscore and replace them with a numerical value provided they are similar . for example a section of my headers look like this :

>NODE_23_length_59792_cov_23.204747_1 
>NODE_23_length_59792_cov_23.204747_2 
>NODE_23_length_59792_cov_23.204747_3 
>NODE_23_length_59792_cov_23.204747_4 
>NODE_23_length_59792_cov_23.204747_5 
>NODE_23_length_59792_cov_23.204747_6 
>NODE_23_length_59792_cov_23.204747_7 
>NODE_23_length_59792_cov_23.204747_8 

the desired output is :

>1_1 
>1_2 
>1_3 
>1_4 
>1_5 
>1_6 
>1_7 
>1_8 

[Mensur Dlakic]

Just curious: why is the replacement better than what you already have? There is important information in that header that will be completely lost, and saving a couple of characters in disk space doesn't seem worth it.

[Pierre Lindenbaum]

dup of Renaming Entries In A Fasta File

[cpad0112]

Up to what character they will not be similar? for eg. after node, after length, after cov?

[Percy]

the last digit after the last underscore