'''[http://www.tcl.tk/man/tcl/TclCmd/string.htm%|%string]''' is an ensemble of
[command%|%commands] for manipulating strings.



** See Also **

   [everything is a string]:   

   [Format]:   

   [string forward compatibility]:   

   [Additional string functions]:   

   [string compare ...]:   

   [regmap], by [SS]:   apply scripts to matching substrings



** Documentation **

   [http://www.tcl.tk/man/tcl/TclCmd/string.htm%|%official reference]:   



** Synopsis **


    :   '''[string bytelength]''' ''string''

    :   '''[string compare]''' ''?'''''-nocase'''''? ?'''''-length int'''''? string1 string2''

    :   '''[string equal]''' ''?'''''-nocase'''''? ?'''''-length int'''''? string1 string2''

    :   '''[string first]''' ''string1 string2 ?startIndex?''

    :   '''[string index]''' ''string charIndex''

    :   '''[string is]''' ''class ?'''''-strict'''''? ?'''''-failindex''' ''varname? string''

    :   '''[string last]''' ''string1 string2 ?startIndex?''

    :   '''[string length]''' ''string''

    :   '''[string map]''' ''?'''''-nocase'''''? charMap string''

    :   '''[string match]''' ''?'''''-nocase'''''? pattern string''

    :   '''[string range]''' ''string first last''

    :   '''[string repeat]''' ''string count''

    :   '''[string replace]''' ''string first last ?newstring?''

    :   '''[string reverse]''' ''string''

    :   '''[string tolower]''' ''string ?first? ?last?''

    :   '''[string totitle]''' ''string ?first? ?last?''

    :   '''[string toupper]''' ''string ?first? ?last?''

    :   '''[string trim]''' ''string ?chars?''

    :   '''[string trimleft]''' ''string ?chars?''

    :   '''[string trimright]''' ''string ?chars?''

    :   '''[string wordend]''' ''string charIndex''

    :   '''[string wordstart]''' ''string charIndex''



** Misc **

Is this correct behavior?

======
% set str {} 
% string is true $str
1
% string is false $str
1
% string is integer $str
1
% string is alpha $str
1
======

Sadly, yes, that is correct.  You'll have to use the '''-strict''' option to
keep empty strings from passing all tests.

This is an unfortunate legacy from the origin of `[string is]` as a tool for
`[entry]` validation, where it's important the empty string pass everything so
that every input doesn't fail immediately.



** Using string functions for binary data **

The following subcommands check for the ByteArray object type internally based
on their bytecode versions (as of 8.5.0):

   * [string range]
   * [string index]
   * [string match]
   * [string length]
   * [string compare] (both objects must be ByteArrays)

The following subcommands force promotion to unicode strings:

   * [string first]
   * [string last]
   * [string map]
   * [string replace]
   * [string reverse]

----

[MG]: Since Tcl 8.5, an index in the [string] commands can include basic math;

======
string range $string $startChar+1 $endChar-1
======

is now equivalent to

======
string range $string [expr {$startChar + 1}] [expr {$endChar - 1}]
======

While the first may be clearer, though, it seems to be (potentially quite a
lot) slower for me, running 8.5a6:

======none
% set string "This is a test string"
This is a test string
% set startChar 3
3
% set endChar 12
12
======
 
======none
% time {string range $string [expr {$startChar+1}] [expr {$endChar-1}]} 500000
2.55498 microseconds per iteration
% time {string range $string $startChar+1 $endChar-1} 500000
5.092856 microseconds per iteration
======

Using [expr] there is quite drastically faster...

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