This extends the command '''string''' to accept a new sub-command '''append''':

 if {[catch {string append}]} then {
    rename string STRING_ORIGINAL
    proc string {cmd args} {
	switch -regexp -- $cmd {
	    ^a(p(p(e(n(d)?)?)?)?)?$ {
		uplevel [list join $args {}]
	    }
	    default {
		if {[catch {
		    set result [uplevel [list STRING_ORIGINAL $cmd] $args]
		} err]} then {
		    return -code error\
			[STRING_ORIGINAL map\
			     [list\
				  STRING_ORIGINAL string\
				  ": must be bytelength,"\
				  ": must be append, bytelength,"]\
			     $err]
		} else {
		    set result
		}
	    }
	}
    }
 }

Now test it:

 % string append ham - and - eggs
 ham-and-eggs
 %

Now test an "original" sub-command:

 % string match -nocase ham and
 0
 % 

Result is 0 -- indeed, that is true. Now test an erraneous situation:

 % string match -nocase ham and eggs
 wrong # args: should be "string match ?-nocase? pattern string"
 % 

The error message hides the '''STRING_ORIGINAL''' and shows up '''string''' instead. Another error:

 % string brumm
 bad option "brumm": must be append, bytelength, compare, (...)
 % 

The error message shows the sub-commands inclusive the newly created append.

See also [wrapping commands].

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[Lars H], 28 July 2006: Wouldn't '''string concat''' have been a more appropriate name? I know I expected a name involving "concat" for this operation when I was a Tcl beginner (and thus tried some monstrous constructions involving [concat] when I really only wanted to do [[set a "$b$c"]]). See also [cconcat].

[NEM]: Yes, '''string concat''' would be better. The -append commands also usually operate on a ''variable''
rather than simply concatenating arguments (e.g. [lappend], [append], and the [dict] variants). Indeed, what
is being appended to in this case? Also, what is the [uplevel] for? Just [[join $args {}]] would do it.

[wdb] My idea was based on the Scheme function ''(string-append str1 str2 ...)''. As a native German speaker, I was more comfortable with the word ''append'' than with ''concatenate'' ... but, if everybody agrees, I'll be happy to change the name of the sub-cmd from '''string append''' to [string concat}. I'm more interested in what it does than how it is named.

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