Use sed command to replace the content of the file (emulate tac command)

Eg:

if cat file1

ABCD
EFGH

Then O/p should be

EFGH
ABCD

sed ‘1! G; h;$!d’ file1

 

Here G command appends to the pattern space,

h command copies pattern buffer to hold buffer

and d command deletes the current patternĀ  space.