We will first see how to do this with tac.

1. The syntax of tac is as follows:

        tac file1 file2 ...

 The tac command can also read from stdin:

        $ seq 5 | tac
        5 
        4 
        3 
        2  
        1

 The default line separator for tac is \n. The -s option will redefine this:

        $ echo "1,2" | tac -s ,
        2
        1

2. This awk script will print lines in the reverse order:

        seq 9 | \
          awk '{ lifo[NR]=$0 } \
            END { for(lno=NR;lno>-1;lno--) { print lifo[lno]; }
                }'

\ in the shell script is used to break a single-line command sequence into multiple lines.