Performs conditional processing in batch programs.

IF [NOT] ERRORLEVEL number command
IF [NOT] string1==string2 command
IF [NOT] EXIST filename command

  NOT               Specifies that Windows should carry out the command only
                    if the condition is false.
  ERRORLEVEL number Specifies a true condition if the last program run returned
                    an exit code equal to or greater than the number specified.
  command           Specifies the command to carry out if the condition is
                    met.
  string1==string2  Specifies a true condition if the specified text strings
                    match.
  EXIST filename    Specifies a true condition if the specified filename
                    exists.