TCL (Tool Command Language) Interview Preparation Guide
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TCL (Tool Command Language) frequently Asked Questions in various TCL job Interviews by interviewer. Get preparation of TCL (Tool Command Language) job interview

11 TCL Questions and Answers:

1 :: What is TCL?

Tcl (Tool Command Language) is a very powerful but easy to
learn dynamic programming language, suitable for a very wide
range of uses, including web and desktop applications,
networking, administration, testing and many more. Open
source and business-friendly, Tcl is a mature yet evolving
language that is truly cross platform(windos,all flavors of
linux,macintosh), easily deployed and highly extensible.

2 :: How TCL works?

After TCL installed on the machine, TCL information got
registred in the machine.
e.g:In Windows Registry

The TCL path is updated in Machine environment.

Then TCL starts working.

1.TCL a Scripting Language. TCL binary comes with
name "tclsh".
When we use TCL,[ For example from Command prompt/Terminal
try to run tclsh ] it provides default prompt "%" to User
and asks for input.

How TCL works??
Each input from user is treated as TCL command.
After providing the command, tclsh fetch(gets) that command
and try to validate/compile/execute and populate(puts) the

% hello
invalid command name "hello"
% set
wrong # args: should be "set varName ?newValue?"
%set say "Hello"

2. When we use TCL, we can provide a Script file as
Example: Create a file "HelloTickle.tcl" containing:

set say "Hello"
puts $say

#tclsh HelloTickle.tcl

How TCL works??
Tcl takes the Argument as a file and try to read the file.
TCL stores the file in memory and reads the file Line by
Line and try to validate/compile.
TCL provides the output and release the memory.


3 :: how to increment eacl element in a list?
eg: incrlist {1 2 3}
=>2 3 4

// it works like incrlist 5 6 7 =>> 6 7 8
proc incrlist args {
set s 0
foreach s $args {
incr s 1
puts $s

//for list
proc incrlist list {
set s 0
foreach s $list {
incr s 1
puts $s

4 :: How to run a package in tcl?

source <package_name>
package require <name>

5 :: How increment a character? For example, I give a and I should get b?

set character "a"
set incremented_char [format %c [expr {[scan $character
puts "Character before incrementing '$character' : After
incrementing '$incremented_char'"

6 :: How to extract "information" from "ccccccccaaabbbbaaaabbinformationabcaaaaaabbbbbbbccbb" in tcl using a single command?

% set
a "ccccccccaaabbbbaaaabbinformationabcaaaaaabbbbbbbccbb"
% set b [string trimleft $a "abc"]
% set c [string trimright $b "abc"]

% set output [string trimright [string trimleft
$a "abc"] "abc"]

7 :: How to Swap 30 & 40 in IP address using TCL script?

There are three solutions.

set a
set b [ string range $a 3 4 ]
set c [ string range $a 6 7 ]
set d [ string replace $a 3 4 $c ]
set e [ string replace $d 6 7 $b]
puts $e

set a
set b [ split $a .]
set u [lindex $b 0]
set v [lindex $b 3]
set x [lindex $b 1]
set y [lindex $b 2]
set z [join "$u $y $x $v" .]
puts $z

set ip
regexp {([0-9]+\.)([0-9]+\.)([0-9]+\.)([0-9]+)} $ip match 1st 2nd 3rd 4th
append new_ip $1st $3rd $2nd $4th
puts $new_ip

8 :: How do you find the length of a string without using string length command in TCL?

set str "lenghtofthisstring"
set len 0
set list1 [ split $str "" ]
foreach value $list1 {
incr len
puts $len

9 :: How to check whether a string is palindrome or not using TCL script?

Code for the above pseudo code.Check if it works!!!!!

gets stdin a
set len [ string length $a ]
set n [ expr $len/2 ]

for { set i 0 } { $i < $n } { incr i 1 } {
set b [ string index $a $i ]
set c [ expr $len - 1 - $i ]
set d [ string index $a $c ]

if {$b != $d} {
puts "not a palindrome"


puts "Palindrome"

10 :: Set ip address as write a script to replace the 30 with 40?

here you can do this in multiple ways

1.regsub 30 $data 40 a
puts $a

this will give you the replaced string

2.string replace $data 3 4 40

this also will give you the replaced value