function onFile( error ) {
		var opts;
		if ( error ) {
			debug( 'Encountered an error when writing temporary input file: %s', error.message );
			return done( error );
		}
		debug( 'Successfully created temporary input file.' );
		opts = {
			'cwd': cwd()
		};
		debug( 'Converting temporary input file...' );
		exec( cmd, opts, onExec );
	}
Callback invoked upon writing a temporary input file.

@private
@param {(Error|null)} error - error object
@returns {void}