:   '''string trim''' ''string ?chars?''

Returns a value equal to ''string'' except that any leading or trailing characters from the set given by ''chars'' are removed. If ''chars'' is not specified then white space is removed (spaces, tabs, newlines, and carriage returns).

<<discussion>>
''See also:''
   * [http://www.tcl.tk/cgi-bin/tct/tip/318.html%|%TIP #318]: Extend Default Whitespace in 'string trim' Beyond ASCII

''[escargo] 2 Jun 2008'' -
This also related to behavior discussed in comp.lang.tcl with the subject,
"string trim not trimming special space characters" (starting on 4 March 2008).

The characters removed by [[string trim ''string'']] (with no ''chars'' argument) are '''not'''
all the ones for which [[string is space ''char'']] returns 1.

I think the tip should also include Unicode nonbreaking spaces. 

[LV] you could either update the TIP page with your concerns, or post a comment over on the [TCT] mailing list.

----
The trimleft will remove the pathname from the beginning of the string and trimright will remove the extension.  
Remember that this command will not save to a variable, therefore you must set the same or another variable:

  % set foo ../returned../
  ../returned../
  % string trim $foo ./
  returned
  % set foo
  ../returned../
  % set foo [string trim $foo ./]
  returned
  % set foo
  returned

[MG] While you can use it for filenames, the [file] command is designed specifically for working with filenames and paths. 
A more general use is to remove leading/trailing white space from a string, something like...

 (Griffiths) 9 % set foo {
 >             this is a test string    }
 
             this is a test string    
 (Griffiths) 10 % string trim $foo
 this is a test string
 
<<discussion>>
----
**See also**
   * [string]
   * [string trimleft]
   * [string trimright]
   * [string map] replaces substrings in a string ([felipel])

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