shell同时读取多个文件合并

现有多个文本文件想要合并在一起，以两个文件为例子吧：

#fileA.txt
this is File A line1
this is File A line2
this is File A line3

#fileB.txt
this is File B line1
this is File B line2
this is File B line3

想要实现交叉的合并，合并后结果为：

this is File A line1
this is File B line1
this is File A line2
this is File B line2
this is File A line3
this is File B line3

---

command1:

paste $fileA $fileB |tr "\t" "\n" > newfile

command2:

awk '{getline line < "fileB.txt";print $0;print line}' fileA.txt