Agfdhyk

I am a fresh learner of Tcl and I faced an issue of understanding this whole concept:

<name of variable> set [split "[string repeat "-,-," [columns]]-",]

columns is a variable with value 6;
How the split will be and which is my whole string?

Thank you all

<name of variable> set [split "[string repeat "-,-," [columns]]-",]

You have to unpack Tcl commands from the inside out because the inner-most nested brackets are executed first.

• 
  columns is a proc that, hopefully, returns an integer.


• then string repeat repeats "-,-," that many times.


• then the double quoted string adds a trailing -
  


• then split should split that "-,-,-,...-" string on commas resulting in *a list of "2 * columns + 1" hyphens*.

Except:

• there is a missing space before the last comma in the split command


• the set command looks like: set varname value (unless you're dealing with an object)

set <name of variable> [split "[string repeat "-,-," [columns]]-" ,]

# ...............................................................^

Demonstrating:

set columns 6

proc columns {} {return $::columns}

set result [split "[string repeat "-,-," [columns]]-" ,]

puts $result

puts [llength $result] ;# should be 13

- - - - - - - - - - - - -

13

You could achieve the same result with:

set result [lrepeat [expr {2 * [columns] + 1}] "-"]

Tcl is actually a very simple language. The entire syntax only has 12 rules: https://www.tcl.tk/man/tcl8.6/TclCmd/Tcl.htm