Tcl - Lists
List is one of the basic data-type available in Tcl. It is used for representing an ordered collection of items. It can include different types of items in the same list. Further, a list can contain another list.
An important thing that needs to be noted is that these lists are represented as strings completely and processed to form individual items when required. So, avoid large lists and in such cases; use array.
Creating a List
The general syntax for list is given below −
set listName { item1 item2 item3 .. itemn }
# or
set listName [list item1 item2 item3]
# or
set listName [split "items separated by a character" split_character]
Some examples are given below −
#!/usr/bin/tclsh
set colorList1 {red green blue}
set colorList2 [list red green blue]
set colorList3 [split "red_green_blue" _]
puts $colorList1
puts $colorList2
puts $colorList3
When the above code is executed, it produces the following result −
red green blue
red green blue
red green blue
Appending Item to a List
The syntax for appending item to a list is given below −
append listName split_character value
# or
lappend listName value
Some examples are given below −
#!/usr/bin/tclsh
set var orange
append var " " "blue"
lappend var "red"
lappend var "green"
puts $var
When the above code is executed, it produces the following result −
orange blue red green
Length of List
The syntax for length of list is given below −
llength listName
Example for length of list is given below −
#!/usr/bin/tclsh
set var {orange blue red green}
puts [llength $var]
When the above code is executed, it produces the following result −
4
List Item at Index
The syntax for selecting list item at specific index is given below −
lindex listname index
Example for list item at index is given below −
#!/usr/bin/tclsh
set var {orange blue red green}
puts [lindex $var 1]
When the above code is executed, it produces the following result −
blue
Insert Item at Index
The syntax for inserting list items at specific index is given below.
linsert listname index value1 value2..valuen
Example for inserting list item at specific index is given below.
#!/usr/bin/tclsh
set var {orange blue red green}
set var [linsert $var 3 black white]
puts $var
When the above code is executed, it produces the following result −
orange blue red black white green
Replace Items at Indices
The syntax for replacing list items at specific indices is given below −
lreplace listname firstindex lastindex value1 value2..valuen
Example for replacing list items at specific indices is given below.
#!/usr/bin/tclsh
set var {orange blue red green}
set var [lreplace $var 2 3 black white]
puts $var
When the above code is executed, it produces the following result −
orange blue black white
Set Item at Index
The syntax for setting list item at specific index is given below −
lset listname index value
Example for setting list item at specific index is given below −
#!/usr/bin/tclsh
set var {orange blue red green}
lset var 0 black
puts $var
When the above code is executed, it produces the following result −
black blue red green
Transform List to Variables
The syntax for copying values to variables is given below −
lassign listname variable1 variable2.. variablen
Example for transforming list into variables is given below −
#!/usr/bin/tclsh
set var {orange blue red green}
lassign $var colour1 colour2
puts $colour1
puts $colour2
When the above code is executed, it produces the following result −
orange
blue
Sorting a List
The syntax for sorting a list is given below −
lsort listname
An example for sorting a list is given below −
#!/usr/bin/tclsh
set var {orange blue red green}
set var [lsort $var]
puts $var
When the above code is executed, it produces the following result −
blue green orange red
