Yes I know - a lot of information in Net. But. Let's try what what they wrote.
Unfortunately this will not work because the :~ syntax expects a value not a variable. To get around this use the CALL command like this:
SET _startchar=2
SET _length=1
SET _donor=884777
CALL SET _substring=%%_donor:~%_startchar%,%_length%%%
ECHO (%_substring%)
Tell me please - what I'm doing wrong?
1) You can try with delayed expansion:
@Echo off
setlocal enableDelayedExpansion
SET _startchar=2
SET _length=1
SET _donor=884777
SET _substring=!_donor:~%_startchar%,%_length%!
ECHO (%_substring%)
2) to make it work with CALL SET you need double % (but it will be slower than the first approach):
@Echo off
::setlocal enableDelayedExpansion
SET _startchar=2
SET _length=1
SET _donor=884777
call SET _substring=%%_donor:~%_startchar%,%_length%%%
ECHO (%_substring%)
3) You can use delayed expansion and for loop. It can be useful if there are nested bracket blocks and the _startchar and _length are defined there.Still will be faster than CALL SET:
@Echo off
setlocal enableDelayedExpansion
SET _startchar=2
SET _length=1
SET _donor=884777
for /f "tokens=1,2 delims=#" %%a in ("%_startchar%#%_length%") do (
SET _substring=!_donor:~%%a,%%b!
)
ECHO (%_substring%)
4) you can use subroutine and delayed expansion :
@Echo off
setlocal enableDelayedExpansion
SET _startchar=2
SET _length=1
SET _donor=884777
call :subString %_donor% %_startchar% %_length% result
echo (%result%)
exit /b %errorlevel%
:subString %1 - the string , %2 - startChar , %3 - length , %4 - returnValue
setlocal enableDelayedExpansion
set "string=%~1"
set res=!string:~%~2,%~3!
endlocal & set "%4=%res%"
exit /b %errorlevel%
%%to%but the latter does not, hence you cannot use the code in command prompt but in a batch file only. Refer to this: How does the Windows Command Interpreter (CMD.EXE) parse scripts?