I have a huge text file which look like this:

36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,3
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,8
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,14
36,53,15596,0.58454577855,0.26119,2.24878677855,0.116147072052964,12

The desired output is this:

36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-03
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-08
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-14
36,53,15596,0.58454577855,0.26119,2.24878677855,0.116147072052964,MI-12

I have tried other relevant posts here and on other communities but could not exactly get what I want.

UPDATE

This is the cross-question (I wanted both Unix/perl answers and batch/powershell solutions for this.) that has interesting answers.

awk approach with sprintf function(to add leading zeros):

awk -F, -v OFS=',' '$8=sprintf("MI-%02d",$8);' file

The output:

36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-03
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-08
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-14
36,53,15596,0.58454577855,0.26119,2.24878677855,0.116147072052964,MI-12

-F, - set comma , as field separator

$8 - points to the eighth field

%02d - format which treats function argument as 2-digit number

Note, the last field in a record can be presented by $NF.

NF is a predefined variable whose value is the number of fields in the current record

So, $NF is the same as $8(for your input)

awk -F, -v OFS=',' '$(NF)=sprintf("MI-%02d", $(NF))' file

You can try using awk:

awk 'BEGIN FS = OFS = "," $NF = sprintf("MI-%02d", $NF); 1' file

Here's perl solution:

$ perl -F',' -lane '$last=$#F;$F[$last]=sprintf("MI-%02d",$F[$last]);print join ",", @F' input.txt 
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-03
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-08
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-14
36,53,15596,0.58454577855,0.26119,2.24878677855,0.116147072052964,MI-12

The -a flag allows us to treat input as array, based on separator specified with -F. Basically we alter last item in that array, and rebuild it via join command.

With input data like:

36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,3 
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,8 
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,14 
36,53,15596,0.58454577855,0.26119,2.24878677855,0.116147072052964,12 

in text.csv

the code below

awk -F"," ' i = 0;
 MyOutLine = "";
 j = NF - 1;
 while ( i < j ) 
 i++;
 MyOutLine = MyOutLine""$i",";
 
 i++;
 x = sprintf( "%.2i", $i );
 y = "MI-"x;
 MyOutLine = MyOutLine""y;
 print MyOutLine; ' ./text.csv 

produces output like:

36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-03
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-08
36,53,90478,0.58699759849,0.33616,4.83449759849,0.0695335954050315,MI-14
36,53,15596,0.58454577855,0.26119,2.24878677855,0.116147072052964,MI-12

Tcl

Here is my solution, done using Tcl which reads from input.csv file and puts the result in output.csv file

set in [open input.csv]
set out [open output.csv w]

while ![eof $in] 
 set line [gets $in]
 set last_comma_pos [string last , $line]
 puts $out [string range $line 0 $last_comma_pos][format MI-%02d [string range $line $last_comma_pos+1 end]]


close $in
close $out

demonstration