I usually forget about tac since I need to do this about once a year, and end up re-inventing the wheel. Off the top of my head:

$ grep -n ^ FILE | sort -nr -t: -k1 | cut -d: -f2

tail -r

Example:

[~]> cat testfile.txt
first line
second line
line 3
last line
[~]> tail -r testfile.txt
last line
line 3
second line
first line

FYI, from the man page: “The default for the -r option is to display all of the input.”

This is true. I actually wanted to not use this method. Actually there are even more methods, like open the file for reading with some file descriptor with exec and use that descriptor with read -u. The way you have done is a good way, and the last line is included which does not depend wether it ends with a new line or an eof. But still you need to set the IFS to partition the contents of the file at the newline characters.

The case in which your code will fail is:

1. If you have a file say with two lines as folows:

   l1
   l2

   where there is no newline after the line 2 , ie. “l2″ ends directly with eof.
   Your code would generate output

   l2
   l1
   

   where the output should be

   l2l1
   

   because there is no newline after l2. Compare output with the program tac which performs the same job as the script.

Where both of our code fails is in:

1. create a file containing the contents:

   h\ne\nl\nl\no
   

   both of our code will output

   h
   e
   l
   l
   o
   

   where the output should be

   h\ne\nl\nl\no
   

So at the end we have come to know that this thing can be done in a lot of ways. The best thing is that i have found one more bug in my code when replying to your comment. This is same as after “@DangerousDaren’s” comment i found one and eliminated.

Thank you for going through the code and commeting with such details. Please let me know if you have any comments or other possibilities. Also i would request you to have a look at the bugfixed version of my code, and the updated description text.

#!/bin/bash
#This code is a part of http://phoxis.wordpress.com
#

file_name="$1"
     #Check if file name is given, and it exists

if [ "$#" -eq 0 ]
  then
   echo "Syntax: $0 filename"
   exit
elif [ ! -f "$file_name" ]
  then
     echo "File \""$file_name"\" does not exist"
     exit
fi

     #Set the IFS variable to \n this enables reading one \n separated
     # line per read

IFS=$'\n'

     #Read from file_name and store contents into array.
arr=( $( < $file_name ) )

     #Count number of lines, and adjust index

i=${#arr[*]}
i=$((i-1))

     #Print the lines in reverse order
while [ $i -ge 0 ]
do
   echo -e "${arr[$i]}"
   i=$((i-1))
done

Note that I’m a bash n00b who’s trying to learn more so if I’m off on my conclusions (very well possible due to my said limited testing), please correct me.

Cheers!

All these stuff, to handle one terminal condition :) , but you can never tell when the overlooked terminal conditions become vital in your application.

You are indeed correct, I guess “two wrongs do make a right” in this case ;-)

i=$(($i-2)) should read i=$(($i-1))