**What is a string?**

Within [Tcl], the basic philosophy is that [everything is a string]. That is to say, Tcl's primary fundamental data structure is an item which is dynamically allocated (size limited only by the machine's memory and any limits put onto Tcl from the operating system or parent process) and which can contain any type of byte (''at least as of Tcl 8.0'' [[is that version right?]]). 

Other data structures (such as [proc], [dict], [list], [handle]) are built on top of this fundamental assumption.  


**The Tcl string command**
string - Manipulate strings

http://purl.org/tcl/home/man/tcl8.5/TclCmd/string.htm

Ensembliform command for manipulating strings.

----

'''[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 is list]

'''[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''

----

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
the [[string is]] command 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:

 % set string "This is a test string"
 This is a test string
 % set startChar 3
 3
 % set endChar 12
 12
 
 % 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...

----

See also:

   * [string forward compatibility]
   * [Additional string functions]
   * [string compare ...]

----
!!!!!!
[Tcl syntax help] -
[Arts and Crafts of Tcl-Tk Programming] -
%| [Category Command] (of [Tcl]) | [Category Data Structure] | [Category String Processing] |%
!!!!!!