IF, CALL, EXIT and %ERRORLEVEL% in a .bat

Question

Can anyone please help me understand the behaviour of %ERRORLEVEL% variable and why it's not being set after a CALL while being inside an IF, i.e. the ECHO %ERRORLEVEL%.2 line?

@ECHO OFF
SET ERRORLEVEL
VERIFY > NUL

ECHO %ERRORLEVEL%.0
IF ERRORLEVEL 1 ECHO SNAFU

IF %ERRORLEVEL% == 0 (
  ECHO %ERRORLEVEL%.1
  CALL :FOO
  ECHO %ERRORLEVEL%.2
  IF ERRORLEVEL 42 ECHO 42.3
)

GOTO :EOF

:FOO
  EXIT /B 42
GOTO :EOF

STDOUT

C:\Users\Ilya.Kozhevnikov\Dropbox>foo.bat
Environment variable ERRORLEVEL not defined
0.0
0.1
0.2
42.3

However, without IF the %ERRORLEVEL% variable is set as expected.

@ECHO OFF
SET ERRORLEVEL
VERIFY > NUL

ECHO %ERRORLEVEL%.0
IF ERRORLEVEL 1 ECHO SNAFU

REM IF %ERRORLEVEL% == 0 (
  ECHO %ERRORLEVEL%.1
  CALL :FOO
  ECHO %ERRORLEVEL%.2
  IF ERRORLEVEL 42 ECHO 42.3
REM )

GOTO :EOF

:FOO
  EXIT /B 42
GOTO :EOF

STDOUT

C:\Users\Ilya.Kozhevnikov\Dropbox>foo.bat
Environment variable ERRORLEVEL not defined
0.0
0.1
42.2
42.3

Answer 1

When the cmd parser reads a line or a block of lines (the code inside the parenthesis), all variable reads are replaced with the value inside the variable before starting to execute the code. If the execution of the code in the block changes the value of the variable, this value can not be seen from inside the same block, as the read operation on the variable does not exist, it was replaced with the value in the variable

To solve it, you need to enable delayed expansion, and, where needed, change the syntax from %var% to !var!, indicating to the parser that the read operation needs to be delayed until the execution of the command.

@ECHO OFF

setlocal enabledelayedexpansion

SET ERRORLEVEL
VERIFY > NUL

ECHO %ERRORLEVEL%.0
IF ERRORLEVEL 1 ECHO SNAFU

IF %ERRORLEVEL% == 0 (
  ECHO !ERRORLEVEL!.1
  CALL :FOO
  ECHO !ERRORLEVEL!.2
  IF ERRORLEVEL 42 ECHO 42.3
)

GOTO :EOF

:FOO
  EXIT /B 42
GOTO :EOF