The man page for llength is 
http://purl.org/tcl/home/man/tcl8.4/TclCmd/llength.htm

This command returns the number of [element]s in the list.  If the string is not a well-formed list, an error will be thrown.

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[caspian]: Make sure to give llength the list, not just the name variable where the list is stored. For example:

 # This is the right way to do it.
 set mylist {a b c}
 llength $mylist

 # This is the WRONG way to do it.
 # This won't return an error, but it will always return "1",
 # no matter how long or short your list is.
 set mylist {a b c}
 llength mylist

This is one of those places where [Tcl]'s treatment of ''bareword literals''
can be frustrating to someone. 

In the second case above, Tcl considers the argument to llength a list.
Therefore, it is going to return the length of the list, which is
equivalent to this list:

        llength [list "mylist"]

[DKF]: The phrase "bareword literals" indicates a deviation from the '''[Tcl] Way'''; the concept does not really operate usefully in Tcl, unlike in a number of other languages (*cough*Perl*cough*).  The '''llength''' command always works with list values, and lists are always values. If you've a list in a variable, you need to get the list out of the variable to work out its length.

[GWM] Note also the slightly unexpected result for:
  llength "a b c"  ;# returns 3 as the string (only one string) is interpreted as a 
list by llength, the spaces making 3 elements. 
  llength "a {b d} c"  ;# is also 3 - the inner braces make a sub-list
  llength {a {b d} c}  ;# also 3 - it is the same as above
  llength "{a {b d} c}" ;# is 1 - the braces inside the string make a sub-list

Also
  
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See also [list], [lappend], [lindex], [linsert], [lrange], [lreplace], [lsearch], [lsort] .
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