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TCL variable name is a variable value

Posted on 2011-05-11
Medium Priority
Last Modified: 2013-11-22
I have a TCL variable. But part of its name is the value of anotehr dynamic variable. For instance, the variable "Bus_Route_$Number" represent Bus route number. But the Number itself is a variable, could be 1,2,3 and etc. It is either from environment variable or runtime execution result of another part of program. Now if I want to retrieve the value of  Bus_Route_$Number, how to specify it. I tried


All did not work.
Question by:gs_kanata
LVL 24

Expert Comment

ID: 35744009
You usually would not do it that way but making Bus_Route an Array, the index then would be you $Number.


Expert Comment

ID: 35757125

Agree with fridom, that is usually not the way to go about since it's not very efficient, but it can be done, of course :-)

This is one way to do it;

set var "\$Bus_Route_$Number"
set value [susbst -nocommands $var]

Lets say $Number contained 42, then $value now has the same data as in ${Bus_Route_42}


Expert Comment

ID: 35757186
Correction it should be subst not susbst
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LVL 53

Expert Comment

ID: 35953341
I've requested that this question be closed as follows:

Accepted answer: 500 points for bummerlord's comment http:/Q_27031495.html#35757125

for the following reason:

This question has been classified as abandoned and is closed as part of the Cleanup Program. See the recommendation for more details.

Author Comment

ID: 35953343
set Number 42
set var "\$Bus_Route_$Number"
set value [subst -nocommands $var]

But I got error when running the above lines

can't read "Bus_Route_42": no such variable
    while executing
"subst -nocommands $var"

Accepted Solution

bummerlord earned 1500 total points
ID: 35985653
That is because you have not yet defined "Bus_Route_42"
42 was just an example.

Complete PoC code attached - it will output;
Variable Bus_Route_42 contains "sample data"

# Define sample environment data
set Bus_Route_42 "sample data" 
set Number 42

# Proof of concept code
set var "\$Bus_Route_$Number"
set value [subst -nocommands $var]
puts stdout "Variable Bus_Route_$Number contains \"$value\""

Open in new window


Author Closing Comment

ID: 35997162
B/c I have to design those variables in advance. It is not so dynamic if there is a wide range of possibilities.

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