Various methods include:
Remove "Nick:" and ","
$remove($2,Nick:,$chr(44))
Get just the text after the colon, except the last character (the comma)
$left($gettok($2,2,58),-1)
Same as above, but remove the comma rather than ignore the last character
$remove($gettok($2,2,58),$chr(44))
Basically the same as above, but get all the text between the ":" and the ","
$gettok($gettok($2,2,58),1,44)
Get just the first 6 characters starting at character 6
$mid($2,6,6)
Same as above, but calculate how long the nick is in case you're using this for more than just a 6 letter nick
$mid($2,6,$calc($len($2) - 6))
Pick whatever you like.
