Tcl Built-In Commands - lassign manual page


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lassign - Assign list elements to variables


lassign list varName ?varName ...?


This command treats the value list as a list and assigns successive elements from that list to the variables given by the varName arguments in order. If there are more variable names than list elements, the remaining variables are set to the empty string. If there are more list elements than variables, a list of unassigned elements is returned.


An illustration of how multiple assignment works, and what happens when there are either too few or too many elements.
lassign {a b c} x y z       ;# Empty return
puts $x                     ;# Prints "a"
puts $y                     ;# Prints "b"
puts $z                     ;# Prints "c"

lassign {d e} x y z         ;# Empty return
puts $x                     ;# Prints "d"
puts $y                     ;# Prints "e"
puts $z                     ;# Prints ""

lassign {f g h i} x y       ;# Returns "h i"
puts $x                     ;# Prints "f"
puts $y                     ;# Prints "g"
The lassign command has other uses. It can be used to create the analogue of the “shift” command in many shell languages like this:
set ::argv [lassign $::argv argumentToReadOff]


lindex, list, lset, set


assign, element, list, multiple, set, variable
Copyright © 1995-1997 Roger E. Critchlow Jr. Copyright © 1992-1999 Karl Lehenbauer & Mark Diekhans Copyright © 2004 Donal K. Fellows