Version 32 of append

Updated 2010-01-09 19:46:07 by PeterLewerin

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?
(EE: 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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