string

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



** See Also **

   [everything is a string]:   

   [Format]:   

   [string forward compatibility]:   

   [Additional string functions]:   

   [string compare ...]:   
   [regmap], by [SS]:   aApply 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]` fFunctions for bBinary data **
TheIn foTcllo, [working suwith bcoinary data] generally mmeands retricting the ckharacters fin
a value tor the Byfirst 256 [unicodeA] charraycters sobjec that typhe ivalue can be neatly
sent through a [chan%|%channelly] bthat is configured
 ton `-translation binary`,
wheire character is encoded as a single byte that has the same value as the
unicode value of the character.  In other words, bionary data is (just text that
meets ofcertain 8constrains.5.0):
Internally, Tcl sometimes * [stores bing ary data ing a more]
 compact form *than [sit
uses foring textual data that contains a broadex]
r ranger of *characters. [ It's notr
typically ngecesary mto be aware of tch]
ese internals, here *is [a list of routing lengs
th]
at, as of * [Changestr ing Tcol/Tk 8.5%|%8.5] mpary take] (boadvanthage objectsf mustan binte rnal
`ByteArray` repres)entation.
The follow  * `[string subcommrandsge]`
 fo  * `[strcing index]`
 p  * `[stroing moatch]`
   * `[striong lengtoh]`
 un  * `[string codmpare]` (both objects must be ByteAringrays:)
The   * [strfollowing firsout]
ines user an * [sintering last]
l   * [s`String` matyp]
e   * [scontraining an areplrace]
y of  * [striungicode characteverse]:
   * `[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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