Parenthesis in variables inside IF blocks

The ) from the resolved variable in your echo statement is prematurely closing the IF block.

Ordinarily, you could fix that by escaping the ) with ^), but you can't modify the environment variable to resolve to C:\Program Files (x86^).

You can prevent this issue by surrounding the variable with quotes.

As a simpler example:

> SET bad=a)b
> IF 1 == 1 ( ECHO %bad% )
b was unexpected at this time.
> IF 1 == 1 ( ECHO "%bad%" )
"a)b"

my suggestion is :

if (condition_TRUE) goto goodbye_parenthesis_BEGIN

goto goodbye_parenthesis_END  ----- line when previous condition is FALSE ----
:goodbye_parenthesis_BEGIN ----- line when previous condition is TRUE ----

...
variable treatment
...

:goodbye_parenthesis_END

First off - you should never use the PATH variable for your own use. It is a reserved environment variable. Using it for your own purposes can break your scripts.

The simplest solution really is to use delayed expansion. As long as your platform uses CMD.EXE then you have access to delayed expansion.

But there is a relatively easy way to make it work without delayed expansion. You can use disappearing quotes. The quote exists at parse time as the name of a FOR variable while the command is parsed. It expands to nothing before execution time.

@echo off

SET mypath=%programFiles(x86)%
echo Perfect output: %mypath%
IF NOT "%mypath%" ==  "" (
  REM Variable is defined
  for %%^" in ("") do echo fixed output:  %%~"%mypath%%%~"
)

pause >nul

EDIT - When to use delayed expansion: Response to comment

I generally only use delayed expansion when it is needed (or more precisely, when it is advantageous). That being said, I usually find it advantageous in some portion of my batch code.

Major Advantages

• Inside a code block in order to see changes to a variable within the block
• When dereferencing the name of a variable. If a variable name is passed in as a parameter, the value of the variable can be gotten via delayed expansion: echo !%1!
• When using variables as arguments to search and replace or substring operations: echo !var:%search%=%replace%!, echo !var:%start%,%len%!.
• Whenever I need to expand the value and not worry about special characters within it needing escaping or quoting: set "var=A&B" & echo !var!

There are other methods to do the above (except the last), but delayed expansion is the easiest, most efficient (fastest to execute), and most reliable option.

Major Disadvantage

• Any FOR variable that contains ! in its value will be corrupted when it is expanded if delayed expansion is enabled. I frequently toggle delayed expansion on and off within a FOR loop to get around the problem.
• It is not good for executing a "macro" (executing code contained within a variable value) because many important phases of command parsing take place prior to the delayed expansion. So many batch features are unavailable to "macros" that are executed via delayed expansion.