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Practical Programming in Tcl & Tk, Third Edition
By Brent B. Welch

Table of Contents
Chapter 5.  Tcl Lists

The join Command

The join command is the inverse of split. It takes a list value and reformats it with specified characters separating the list elements. In doing so, it removes any curly braces from the string representation of the list that are used to group the top-level elements. For example:

join {1 {2 3} {4 5 6}}:
=> 1:2 3:4 5 6 

If the treatment of braces is puzzling, remember that the first value is parsed into a list. The braces around element values disappear in the process. Example 5-9 shows a way to implement join in a Tcl procedure, which may help to understand the process:

Example 5-9 Implementing join in Tcl.
proc join {list sep} {
   set s {}   ;# s is the current separator
   set result {}
   foreach x $list {
      append result $s $x
      set s $sep
   return $result

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