On Thu, 7 Sep 2006, Arnaud Bervas wrote: Please show a little piece of script that demonstrates the problem. Looking at the above, the second variant will surely not work, for this reason: when you use the "$" form of a loop control variable, it works by "string substitution". Before the command line is parsed, all occurrences of "$i" are replaced by the current numerical value of i. This allows you to use "$i" in string contexts such as variable names: genr foo$i = ... But it means that in "$j =$i+1", you are trying to assign a value to a numeric constant on the left-hand side, as in 3 = 10+1 Allin.