Function InteractiveBackend

src/backend/tcop/postgres.c:332–412

 */

static int
InteractiveBackend(StringInfo inBuf)
{
	int			c;				/* character read from getc() */

	/*
	 * display a prompt and obtain input from the user
	 */
	printf("backend> ");
	fflush(stdout);

	resetStringInfo(inBuf);

	/*
	 * Read characters until EOF or the appropriate delimiter is seen.
	 */
	while ((c = interactive_getc()) != EOF)
	{
		if (c == '\n')
		{
			if (UseSemiNewlineNewline)
			{
				/*
				 * In -j mode, semicolon followed by two newlines ends the
				 * command; otherwise treat newline as regular character.
				 */
				if (inBuf->len > 1 &&
					inBuf->data[inBuf->len - 1] == '\n' &&
					inBuf->data[inBuf->len - 2] == ';')
				{
					/* might as well drop the second newline */
					break;
				}
			}
			else
			{
				/*
				 * In plain mode, newline ends the command unless preceded by
				 * backslash.
				 */
				if (inBuf->len > 0 &&
					inBuf->data[inBuf->len - 1] == '\\')
				{
					/* discard backslash from inBuf */
					inBuf->data[--inBuf->len] = '\0';
					/* discard newline too */
					continue;
				}
				else
				{
					/* keep the newline character, but end the command */
					appendStringInfoChar(inBuf, '\n');
					break;
				}
			}
		}

		/* Not newline, or newline treated as regular character */