Quote:

It's not possible to select all the nicknames. You can only select one at a time through /sline.


Yes it is possible.

From the help file

/sline [-a|r] <#channel> <N|nick>
Selects or deselects lines in a channel nickname listbox. It can select either the Nth nickname in a listbox, or a specified nickname.

If you do not specify any switches, any existing selections in the listbox are cleared. If you specify the -a switch then the specified is selected without affecting the selection states of other lines. If you specify the -r switch then the specified item is deselected.

Darkmnm,

Code:
alias getnicks {
  if ($active ischan) {
    var %x = $nick($active,0)
    while (%x) {
      sline -a $active %x
      msg $nick($active,%x) Hello $nick($active,%x)
      dec %x
    }
  }
}