I thought I understood sed but I guess not. I have the following two files, in which I want to replace the "why" and "huh" lines with one different line. No whitespace at all.

> 
> test.txt:
> 
> 
> 

```
hi
why
huh
hi
why
huh

```

> 
> test2.txt:
> 
> 
> 

```
1
hi
why
huh
hi
why
huh

```

The following two commands give the following results:

```
sed "N; s/<why\/>\n<huh\/>/yo/g" test.txt > out.txt

out.txt:
hi
why
huh
hi
yo

sed "N; s/<why\/>\n<huh\/>/yo/g" test2.txt > out2.txt

out2.txt:
1
hi
yo
hi
why
huh

```

What am I not understanding about sed? Why don't both output files contain the following:

```
hi
yo
hi
yo

```