Version 20 of append

Updated 2009-04-24 06:47:14 by AF

***COMMAND append - Append to variable

***USAGE append varName ?value value value ...?

***CONTEXT TCL core command

***DESCRIPTION Append all of the value arguments to the current value of variable varName. If varName doesn't exist, it is given a value equal to the concatenation of all the value arguments. This command provides an efficient way to build up long variables incrementally. For example, `append a $b is much more efficient than `set a $a$b if $a is long.

***MAN PAGE http://www.tcl.tk/man/tcl8.5/TclCmd/append.htm

***SEE ALSO other string functions: string

similar functions for lists: concat, lappend

***EXAMPLES Building a string of comma-separated numbers piecemeal using a loop.

 set var 0
 for {set i 1} {$i<=10} {incr i} {
    append var "," $i
 }
 puts $var
 # Prints 0,1,2,3,4,5,6,7,8,9,10

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NOTE: The append command is a *string* command. If you want to play with lists, definitely use the concat or lappend commands.

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Is the result of an append of two lists a list as you might expect it? (Peter Lewerin: Yes, because append is not lappend.) (EE: Erm, NO. The result of an append of two lists is a string, which, if it can form a valid list, will shimmer into list form next time it is treated as one.)

 set a [list a b c]
 set b [list 1 2 3]
 append a $b
 puts $a

Note that the third element of this new list is not c, but c1. Does anyone know if there are cases where an append would result in something not a list?

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Here's an example of such a case:

 set l1 [list a {b c}]
 set l2 [list {d e} f]
 append l1 $l2
 llength $l1

RS: The intended functionality seems to me to be closer to concat. But if you wish to use append, just add an extra space to separate the parts:

 append l1 " " $l2 

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