[HJG] 2012-12-29 - Demo for re-formatting string to list.

======
 # http://wiki.tcl.tk/37505
 # for-mat2.tcl - HaJo Gurt - 2012-12-29

 #: Re-Format long string to a list of filenames/URLs
 # e.g. to be used with  "wget -i file"

  set Hdr "For-Mat2"

 ####+####1####+####2####+####3####+####4####+####5####+####6####+####7####+###
 ## Console-settings, to allow running in wish as well as in tclsh:
   catch { console show }
   catch { wm withdraw . }
 # catch { console eval { .console config -bg grey -fg blue } }
 # Resize & put at top-right corner on 1024x768:
 ##catch { console eval { wm geometry . 56x12+550+0 } }
   catch { console title "$Hdr" }

   proc q {} { exit }
 ####+####1####+####2####+####3####+####4####+####5####+####6####+####7####+###
   puts "# $Hdr:"

 # set PL  {bild01.jpg bild02.jpg bild03.jpg} 
 ##
 # set P1 "http://blah.de/fasel/"
 # set P2 "bild01.jpg"
 ##
 # set url "http://blah.de/fasel/bild01.jpg"

   set P1 "http://blah.de/fasel/"
   set PS {bild01.jpg,bild02.jpg,bild03.jpg} 
   puts "# PS=$PS."

   set PL  [string map -nocase { "," " "} $PS]
   puts "# PL=$PL."

   set i 0
   foreach P2 $PL {
     incr i
     set url "$P1$P2"
     set filename "XY_$P2"

   # puts "$i.   URL=$url."
   # puts "filename=$filename."
     puts $url
   }
   puts "# Done."
 #.
======

Output:
======
# For-Mat2:
# PS=bild01.jpg,bild02.jpg,bild03.jpg.
# PL=bild01.jpg bild02.jpg bild03.jpg.
http://blah.de/fasel/bild01.jpg
http://blah.de/fasel/bild02.jpg
http://blah.de/fasel/bild03.jpg
# Done.
======

[JJS] 2013-01-04 - [[string map]] doesn't convert a string to a list. In your particular example, it converts a string into another string that can be automagically interpreted as a list of multiple items, if needed. What you want is


======
set PL [split $PS ,]
======

which actually converts a string to a list. Furthermore, your [[string map]] approach is susceptible to all the usual problems that can arise when you treat a string as a list:

   1. If the items contain spaces, then the number of list elements is thrown off.
   1. If the items contain braces, then the automagic conversion may fail.

For example,


======
(System32) 69 % set PS {{one,two,}three}
{one,two,}three
(System32) 70 % set PL [string map {"," " "} $PS]
{one two }three
(System32) 71 % lindex $PL 0
list element in braces followed by "three" instead of space
(System32) 72 % set PL [split $PS ,]
\{one two \}three
(System32) 73 % lindex $PL 0
{one
======

----

'''See also:''' 
[for], [foreach], [I love foreach], 
[string], 
[regexp], [regsub], [Regular Expression Examples]

<<categories>>Example