Shell Programming and Scripting

Hi, I am having a file and grabbed the contents of the field according to field widths. The command i used is:
awk 'BEGIN{FIELDWIDTHS="10 25 20 14 6 10"}{print$4,$5,$6}' newtext.text >test1.txt
i got the output for example:

val1 val2 val3
<blank> val5 val6
val7 <blank> val9

now i want to fill the blank spaces(shown by <blank> here) in row 2 column 1 and in row3 column 2 with 'null'. So how could i do this. Pleas Suggest

You can use something like this:

Code:

awk 'BEGIN {
  FIELDWIDTHS = "10 25 20 14 6 10" 
  begin = 4; end = 6
  }
{ 
  for (i=begin; i<=end; i++)
    printf "%s", isnull($i) (i == end ? RS : FS)
    }
func isnull(field) {
  return field ~ /^[[:blank:]]*$/ ? "null" : field 
  }' infile

With the word "null" or the NUL (\0) character?

with "null" word