I like to rename a file based on the first line. Here is an example of what I need to do.

File: 034568.dat has 2000 lines with first line as
HIOSPAD23409JHK90000
I like to extract 3 characters from 5th column and rename the file to PAD_034568.dat.

Really appreciate your help.
Viv

When you're sure it works, change 'cp' to 'mv':

#!/bin/ksh

# no error checking
myfile=034568.dat
prevar=$(head -1 "$myfile"| cut -c5-7)

cp "$myfile" "${prevar}_${myfile}"

Thanks for your response, being a UNIX novice I have another Q related to this...

Now if I want to put this into a script to execute against unknown filename(s), how would I accomplish that?!

Thanks

Consider this:

#!/bin/ksh
# UNTESTED
cd /your/directory
for myfile in $*
do
  if [[ -f $myfile ]]
  then
      prevar=$(head -1 "$myfile"| cut -c5-7)
      cp "$myfile" "${prevar}_${myfile}"
  fi
done

The above script changes to a /your/directory. That's where your files are.

If your script is called x.ss, execute it with your file names:

x.ss 034568.dat file2.dat file3.dat

if the file exists, it executes the commands.

awk  'FNR==1{
 cmd = "mv "FILENAME" "substr($0,5,3)"_"FILENAME
 system(cmd)
}' *.dat