merge two text file in one without duplicate header in bash

I have two files that looks like this:

file1.txt

ID group gender age
a 1 m 55
b 1 f 54
c 2 m 53
... etc


file2.txt

ID group gender age
l 1 m 64
m 2 f 94
n 2 m 93
... etc

Desired output:

ID group gender age
a 1 m 55
b 1 f 54
c 2 m 53
.
l 1 m 64
m 2 f 94
n 2 m 93
.

Which means to the header only show once.I tried head -n 1 file1.txt > merge.txt; tail -n +2 -q *.txt >> merge.txt, In my real file1.txt has 87394750 row and file2.txt has 369765446 rows,it’s spend a lot of time.Any ideas? Many thanks!

>Solution :

Use cp then sed:

cp file1.txt merge.txt; sed 1d file2.txt >> merge.txt

sed 1d skips the first line.

To skip more lines, use sed 1,nd, where n is the total number of lines to skip.