Accessing variables in TCL across scopes - tcl

Question

I'm trying to learn tcl scripting. My req is very simple. I need to access the array "args" in the second if condition in the for loop. I tried the code below. Since "argv" scope is limited to second if condition, it is NOT accessible in for loop
Then I tried declaring argv as global var -
array set args {}
right below the ned of first if condition. Even after declaring "args" as global array did NOT help.
How do I access the variable in the cope of second if contion, in the for loop below ?
if {$argc != 4} {
puts "Insufficient arguments"
exit 1
}
if { $::argc > 0 } {
set i 1
foreach arg $::argv {
puts "argument $i is $arg"
set args(i) arg
incr i
}
} else {
puts "no command line argument passed"
}
for {set x 0} { $x<2 } {incr x} {
puts "Arrray: [lindex $args $x]"
}

Answer 1

For your original code, this is the error I get:
can't read "args": variable is array
while executing
"lindex $args $x"
("for" body line 2)
invoked from within
"for {set x 0} { $x<2 } {incr x} {
puts "Arrray: [lindex $args $x]"
}"
(file "main.tcl" line 20)
In Tcl, arrays are not lists. You have to write
for {set x 0} { $x<2 } {incr x} {
puts "Arrray: $args($x)"
}
But then I get this:
can't read "args(0)": no such element in array
while executing
"puts "Arrray: $args($x)""
("for" body line 2)
invoked from within
"for {set x 0} { $x<2 } {incr x} {
puts "Arrray: $args($x)"
}"
(file "main.tcl" line 20)
Well there's several problems here. You're setting array elements starting with index 1 but reading them starting with index 0. So let's correct that to 0 everywhere:
set i 0
But also you're missing some $'s in the setting of the elements:
set args($i) $arg
That looks better. Final code:
if {$argc != 4} {
puts "Insufficient arguments"
exit 1
}
if { $::argc > 0 } {
set i 0
foreach arg $::argv {
puts "argument $i is $arg"
set args($i) $arg
incr i
}
} else {
puts "no command line argument passed"
}
for {set x 0} { $x<2 } {incr x} {
puts "Arrray: $args($x)"
}
So, scope wasn't quite the issue. You're getting there though!

Answer 2

Tcl does not import globals by default. You need to import your globals:
global args
set args(i) arg
Some people prefer to import globals at the top of the proc:
global args
if {$argc != 4} {
puts "Insufficient arguments"
exit 1
}
if { $::argc > 0 } {
set i 1
....
See: https://www.tcl.tk/man/tcl8.7/TclCmd/global.htm
Alternatively, you can directly access the global namespace, in fact you're already using that syntax with ::argc:
set ::args(i) arg