Given an input file , reverse every two lines of the file and print the output.

Ex:-
Input file content --
$ cat st.txt
1
2
3
4
5
6
7
8
9
10

Output --
2
1
4
3
6
5
8
7
10
9
-----------------------------------------------------------
Solution 1:- Using awk command
awk '{if(NR%2==1) { line=$0 } else { print $0"\n"line }}' st.txt

Solution 2:- Using sed command (looks elegant but complicated until you get your head around it)
sed -n 'x;N;G;h;$p' st.txt