Shell Programming and Scripting

 
echo `date +%Y%j` `cat -n /home/user/FILENAME.dat |awk '{printf "%08s", $2}'`

$ cat infile
20120201 col2 col3
20120201 col2 col3

$ awk '{print dte,$0}' dte=$(date +%Y%j) infile

awk '{print dte,$0}' dte=$(date +%Y%j) FILENAME

 
Output:
2012195 20120427

x=`cat -n /home/user/FILENAME.dat |awk '{printf "%08s", $2}'`; echo `date +"%Y%j" -d "$x"` $x

$ cat infile
20120201 col2 col3
20120427 col2 col3
$
$ while read x y; do echo "$(date -d$x +%Y%j) $x"; done < infile
2012032 20120201
2012118 20120427
$

 
cat FILENAME.dat
20120427

echo "$(date -d`cat FILENAME.dat` +%Y%j) $(cat FILENAME.dat)"