string

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'''[http://www.tcl.tk/man/tcl/TclCmd/string.htm%|%string]''' is an ensemble of
[routine%|%routines] for manipulating [eias%|%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 cat]''' ''?string ...?''<<br>>          (new in Tcl 8.6.2)

    :   '''[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''



** Missing Functionality **

[pyk] 2020-04-08:  `string` is currently missing a routine, perhaps called
`string common`, that indicates the character at which two strings diverge.
Desirable options include -start and -direction.


** 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 **

In Tcl, [working with binary data] generally means retricting the characters in
a value to the first 256 [unicode] characters so that the value can be neatly
sent through a [chan%|%channel] that is configured to `-translation binary`,
where character is encoded as a single byte that has the same value as the
unicode value of the character.  In other words, binary data is just text that
meets certain constrains.

Internally, Tcl sometimes stores binary data in a more compact form than it
uses for textual data that contains a broader ranger of characters.  It's not
typically necesary to be aware of these internals, here is a list of routines
that, as of [Changes in Tcl/Tk 8.5%|%8.5] may take advantage of an internal
`ByteArray` representation.

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

The following routines user an internal `String` type containing an array of unicode characters:

   * `[string first]`   * `[string last]1`
   * `[string map]`
   * `[string replace]`
   * `[string reverse]`

----

[MG]: Since [Changes in Tcl/Tk 8.5%|%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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