Batch file: Find if substring is in string (not in a file)

To find a text in the Var, Example:

var_text="demo string test"
Echo.%var_text% | findstr /C:"test">nul && (
    echo "found test" 
    ) || Echo.%var_text% | findstr /C:"String">nul && (
             echo "found String with S uppercase letter" 
    ) || (
             echo "Not Found " 
    )

LEGEND:

1. & Execute_that AND execute_this
2. || Ex: Execute_that IF_FAIL execute this
3. && Ex: Execute_that IF_SUCCESSFUL execute this
4. >nul no echo result of command
5. findstr
6. /C: Use string as a literal search string

I'm probably coming a bit too late with this answer, but the accepted answer only works for checking whether a "hard-coded string" is a part of the search string.

For dynamic search, you would have to do this:

SET searchString=abcd1234
SET key=cd123

CALL SET keyRemoved=%%searchString:%key%=%%

IF NOT "x%keyRemoved%"=="x%searchString%" (
    ECHO Contains.
)

Note: You can take the two variables as arguments.

ECHO %String%| FINDSTR /C:"%Substring%" && (Instructions)

Better answer was here:

set "i=hello " world"
set i|find """" >nul && echo contains || echo not_contains

The solutions that search a file for a substring can also search a string, eg. find or findstr.
In your case, the easy solution would be to pipe a string into the command instead of supplying a filename eg.

case-sensitive string:
echo "abcdefg" | find "bcd"

ignore case of string:
echo "abcdefg" | find /I "bcd"

IF no match found, you will get a blank line response on CMD and %ERRORLEVEL% set to 1

Built on @user839791's answer, but I've added a few more things.

@echo off
rem --Set variable below--
set var=condition

rem --Uncomment below line to display contents of variable--
::echo The variable is %var%

rem --Change condition to desired string below--
ECHO.%var%| FIND /I "condition">Nul && (  
  rem --Occurs if the string is found--
  Echo.Variable is "condition"
  color C
  pause
) || (
  rem --Occurs if the string isn't found--
  Echo.Variable is not "condition"
  color A
  pause
)

Best approach for me would be this:

call :findInString "HelloWorld" "World"

:findInString
ECHO.%1 | FIND /I %2>Nul && ( 
  Echo.Found
) || (
  Echo.Not found
)

Yes, We can find the subString in the String:

echo.%data% | FINDSTR /I "POS">Nul && (SET var=POS) || (SET noVar="variable not found")

echo.%data% | FINDSTR /I "TD1">Nul && (SET var=TD1) || (SET noVar="variable not found")

GOTO %var%

:POS   
echo processes inside POS  
GOTO END

:TD1   
echo processes inside TD1

:END