Dave Morriss was recently having problems because he was trying
to do something like:

set index [expr [exec date +%W]%[llength $pop_server_list]]

but during the 9th and 9th week of the year, he got errors - 08 and 09
are not valid octal numbers in Tcl.

Some of the solutions provided were:

From George A. Howlett , we got:

set wknum [format "%g" [exec date +%W]]
set index [expr [exec $wknum%[llength $pop_server_list]]

From Fred Feirtag  :

set index [expr (1[exec date +%W]-100)%[llength $pop_server_list]]

From Dan R. Schenck :

set index [expr [string trimleft [exec date +%W] 0]%[llength $pop_server_list]]