string trim

• Synopsis
• See Also
• Description
• Examples
  • Example 1
  • Example 2
• What Constitutes Whitespace
• Discussion

string trim removes characters from the beginning and end of a string.

Synopsis

string trim string ?chars?

See Also

string map

Replace substrings in a string.

string

All the other "string"-commands.

Trimming indentation

textutil

Provides regular expression variants of the string trim commands, as well as trimPrefix an trimEmptyHeading.

Description

Returns a value equal to string except that any leading or trailing characters that occur in chars are removed.
If chars is not specified then white space is removed (space, tab, newline, and carriage return). TIP 443 added null, zero width no break space (+UFEFF), word joiner (+U2060, zero width space (+U200B), and any Unicode character that has the "white space" property.

Examples

Example 1

# 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>"
#. 

Output:

< Hello ! > <Hello !>
<*** Hello_###> < Hello>

Example 2

# http://codepad.org/b4bHNWjo
 set s1 " * Hello ** "
 set s2 [string trim $s1]
 set s3 [string trim $s1 " *"]
 puts "<$s1>\n<$s2>\n<$s3>"

Output:

< * Hello ** >
<* Hello **>
<Hello>

What Constitutes Whitespace

See TIP #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.

Discussion

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

pyk 2015-05-17: The added examples are better than what previously passed as examples on this page. I've adjusted them to conform to the Tcl minimal escaping style. @MiHa: if you as the author of the new examples take exception to that, just change them back to your own preferred style.
As far as putting the Description section before the Synopsis section, I think there's enough precedent having an unnamed summary with the description coming after the synopsis to justify leaving the current order as it is.

MiHa 2015-05-18: I don't like that style , so I changed it back.
I feel a document should start with a proper headline,
so what is the rationale behind the description starting late in the page ?