as with most things in Linux there are several ways to dot his. you could read the number of lines by using wc -l and use this number in loop of a bash program to print the file line by line in reversed order.
however, as stated, there are more ways to do this. This most easy way to read a file in reversed order in Linux is making use of the tac command. The tac command will do exactly as described above without any line of coding or any other smart trick. It just reads a file and print the content in reversed order to your screen (or pipe it into another file).
NAME tac - concatenate and print files in reverse SYNOPSIS tac [OPTION]... [FILE]... DESCRIPTION Write each FILE to standard output, last line first. With no FILE, or when FILE is -, read standard input. Mandatory arguments to long options are mandatory for short options too. -b, --before attach the separator before instead of after -r, --regex interpret the separator as a regular expression -s, --separator=STRING use STRING as the separator instead of newline --help display this help and exit --version output version information and exit