join - Create a string by joining together list elements
The list argument must be a valid Tcl list. This command returns the
string formed by joining all of the elements of list together with
joinString separating each adjacent pair of elements. The
joinString argument defaults to a space character.
Making a comma-separated list:
set data {1 2 3 4 5}
join $data ", "
→ 1, 2, 3, 4, 5
Using join to flatten a list by a single level:
set data {1 {2 3} 4 {5 {6 7} 8}}
join $data
→ 1 2 3 4 5 {6 7} 8
list(n), lappend(n), split(n)
element, join, list, separator