Let's say I have this code :
set a 1
set a.b a
set thing a.b
puts [subst $$thing]
The answer I would expect on the last line would be "a", but tcl answers 1.b I tried to put \ everywhere before the . but it didn't changed anything.
Is there away to get a from thing variable ?
Tcl does not double evaluate two consecutive dollar signs.
The $thing characters in your command subst $$thing are first replaced by the value of $thing, which is a.b.
Subsequently, the subst command is evaluated like this:
subst $a.b
The above subst command replaces $a with 1, which explains why you get 1.b returned.
A reliable way to do multiple variable interpolation is with the set command without a second argument. Chain together multiple set commands to interpolate multiple times.
puts [set thing]
--> a.b
puts [set [set thing]]
--> a
puts [set [set [set thing]]]
--> 1