** Description **

Returns a value equal to ''string'' except that any leading or trailing characters 
that occur in ''chars'' are removed. <<br>>
If ''chars'' is not specified then white space is removed (spaces, tabs, newlines, and carriage returns).


'''`[string] trim`''' removes characters from the beginning and end of a string.


** Synopsis **

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

** Demo **
======
# http://ideone.com/IX2f6Y
 set s1 " Hello "
 set s2 [string trim $s1]
 puts "<$s1> <$s2>"
#
 set s1 "*** Hello_###"
 set s2 [ string trim $s1 "*#_" ]
 puts "<$s1> <$s2>"
#. 
======
'''Result:'''
======none
< Hello > <Hello>
<*** Hello_###> < Hello>
======


** See Also **
   * [string map]:   Replace substrings in a string.
   * [string]    :   all the other "string"-commands
   * [Trimming indentation]:   
   * [textutil%|%textutil]:   Provides [regular expressions%|%regular expression] variants of the `string trim` commands, as well as `trimPrefix` an `trimEmptyHeading`.


** What Constitutes Whitespace **

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

[escargo] 2008-06-02:
This also related to behavior discussed in [comp.lang.tcl] with the subject,
"string trim not trimming special space characters" (starting on 2008-03-04).

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.

[MiHa] 2015-05-17: As I already ranted, missing examples are a common shortcoming in the docs. <<br>>
As an example, how I would like examples done (here in the wiki, as well as in the help-system <<br>>
that comes with the tcl/tk-installation,
I added a demo-section, <<br>>
with a link to an online-compiler, where this example can be seen "live".


<<categories>> Tcl syntax help | Command | String Processing