Composer/Migrations.php
private static function checkAndMoveFile($sourceMigrationFile, $appMigrationDir, IOInterface $io)
    {
        //get the file name
        $explodedPath = explode('/', $sourceMigrationFile);
        $filename = array_pop($explodedPath);
        
        if (file_exists($appMigrationDir.'/'.$filename)) {
            if (md5_file($appMigrationDir.'/'.$filename) === md5_file($sourceMigrationFile)) {
                if ($io->isVeryVerbose()) {
                    $io->write("<info>found that $sourceMigrationFile is equal"
                          . " to $appMigrationDir/$filename</info>");
                }
                $doTheMove = false;
            } else {
                $doTheMove = $io->askConfirmation("<question>The file \n"
                      . " \t$sourceMigrationFile\n has the same name than the previous "
                      . "migrated file located at \n\t$appMigrationDir/$filename\n "
                      . "but the content is not equal.\n Overwrite the file ?[y,N]", false);
            }
        } else {
            $doTheMove = true;
        }
        
        //move the file
        if ($doTheMove) {
            $fs = new Filesystem();
            $fs->copy($sourceMigrationFile, $appMigrationDir.'/'.$filename);
            $io->write("<info>Importing '$filename' migration file</info>");
            return true;
        }
        
        return false;
    }
private static function checkAndMoveFile($sourceMigrationFile, $appMigrationDir, IOInterface $io)
    {
        //get the file name
        $explodedPath = explode('/', $sourceMigrationFile);
        $filename = array_pop($explodedPath);
        
        if (file_exists($appMigrationDir.'/'.$filename)) {
            if (md5_file($appMigrationDir.'/'.$filename) === md5_file($sourceMigrationFile)) {
                if ($io->isVeryVerbose()) {
                    $io->write("<info>found that $sourceMigrationFile is equal"
                          . " to $appMigrationDir/$filename</info>");
                }
                $doTheMove = false;
            } else {
                $doTheMove = $io->askConfirmation("<question>The file \n"
                      . " \t$sourceMigrationFile\n has the same name than the previous "
                      . "migrated file located at \n\t$appMigrationDir/$filename\n "
                      . "but the content is not equal.\n Overwrite the file ?[y,N]", false);
            }
        } else {
            $doTheMove = true;
        }
        
        //move the file
        if ($doTheMove) {
            $fs = new Filesystem();
            $fs->copy($sourceMigrationFile, $appMigrationDir.'/'.$filename);
            $io->write("<info>Importing '$filename' migration file</info>");
            return true;
        }
        
        return false;
    }
check if the file exists in dest dir, and if the file is equal. If not,
move the file do destination dir.

@param string $sourceMigrationFile
@param string $appMigrationDir
@param IOInterface $io
@return boolean