How to write the different variable value in a file in TCL

How to write the different variable value in TCL using the foreach loop.

Here this is the situation:

set data1 "This is 开发者_开发百科Data1 Value\n"
set data2  "This is Data2 Value"
set data3  "\nThis is Data3 Value\n"

foreach different_content {data1 data2 data3} {

  puts $fo $different_content
}
close $fo
}  

But it is not working.

There are multiple problems with the fragment of code. The first and simplest error is that you have not anywhere opened the file fo. Unless that is done elsewhere in code you haven't shown here, you need to add something like

set fo [open test.txt w]

before your foreach loop.

The second problem is that your code is going to write this content to the file:

data1
data2
data3

but probably you intend for it to write this content:

This is Data1 Value

This is Data2 Value

This is Data3 Value

Here the error is more subtle. What your loop is doing is setting different_content to the name of each variable of interest, but you want the value of those variables. Essentially you need to doubly dereference the different_content variable. Adding a $ at the start of the variable name gives you one level of dereferencing. Unfortunately with Tcl, you can't just slap another $ onto the front to get the second level. But you can use the set command. After all, $ is just syntacic sugar for set: $foo is identical to [set foo]. Therefore, I believe you need to rewrite the body of your loop as follows:

puts $fo [set $different_content]

So, putting it all together:

set data1 "This is Data1 Value\n"
set data2  "This is Data2 Value"
set data3  "\nThis is Data3 Value\n"

set fo [open test.txt w]
foreach different_content {data1 data2 data3} {
    puts $fo [set $different_content]
}
close $fo

Eric's answer is great, but there's two other ways to write that foreach loop:

Method 1 (read the variables earlier):

foreach different_content [list $data1 $data2 $data3] {
    puts $fo $different_content
}

Method 2 (use upvar 0 to make named aliases to variables):

foreach different_var {data1 data2 data3} {
    upvar 0 $different_var different_content
    puts $fo $different_content
}

You need to open the filehandle you are referring to as $fo but have not actually opened:

set data1 "This is Data1 Value\n"
set data2  "This is Data2 Value"
set data3  "\nThis is Data3 Value\n"

set fo [open 'test.txt']

foreach different_content {data1 data2 data3} {
  puts $fo $different_content
}

close $fo