Ok. Thanks again. I think I've found what I need. (on lines of 'inpch' that contain 'TH' I change the field at position $pos to be $new, preserving spacing made of 'space's and/or tabs). If anyone comes up with sth. simpler...
Ruda
(The script is for 'rc', btw., so that the concatanation on the 3rd line work.)
9 awk '
/TH/ {n = split($0, spaces, /[^ ]+/);
$'$pos'='$new';
line = "";
for(i = 1; i < n; i++)
line = line spaces[i] $(i);
line = line spaces[n];
print line;
next;}
{print}
' inpch
