If the url list is large then using /write so many times will be very slow, I'd use something like this instead:

Code:
alias urls {
  .fopen -no urls $+(",$remove($1-,"),")
  filter -fk urls.ini addurl
  .fclose urls
}
alias addurl {
  if ([*] !iswm $1-) .fwrite -n urls $gettok($1-,2,61)
}


/urls <file>