Shell Programming and Scripting

Thanks Mirni!!

Need a sligh modification.

I would like the replacement to happen only for the first 1000 rows.
I know i have to add some where NR<=1000. But not sure exactly where.

Code:

 
awk 'function repl(s,f,t,v)
{ return substr(s,1,f-1) sprintf("%-*s", t-f+1, v) substr(s,t+1) }
{ a=repl($0,96,98,"ABC")
  a=repl(a,99,113,"DEF")
  a=repl(a,190,198,"XYZ")
  print a
}' infile

Help is appreciated.

What should it do for the rest of the rows? Print them unmodified?

Code:

 
awk 'function repl(s,f,t,v)
{ return substr(s,1,f-1) sprintf("%-*s", t-f+1, v) substr(s,t+1) }
NR<=1000 { a=repl($0,96,98,"ABC")
  a=repl(a,99,113,"DEF")
  a=repl(a,190,198,"XYZ")
  print a
} NR>1000' infile

The first expression with NR tells it when to execute that entire code block. The second expression with NR implicitly tells it when to print. So when NR<=1000, the code block runs and prints a, and the NR>1000 expression does not print the line. When NR>1000, the code block is skipped, but the NR>1000 expression prints entire lines.