Function PageOutput

src/fe_utils/print.c:2975–3019

* PageOutput * * Tests if pager is needed and returns appropriate FILE pointer. * * If the topt argument is NULL no pager is used. */

 * If the topt argument is NULL no pager is used.
 */
FILE *
PageOutput(int lines, const printTableOpt *topt)
{
	/* check whether we need / can / are supposed to use pager */
	if (topt && topt->pager && isatty(fileno(stdin)) && isatty(fileno(stdout)))
	{
#ifdef TIOCGWINSZ
		unsigned short int pager = topt->pager;
		int			min_lines = topt->pager_min_lines;
		int			result;
		struct winsize screen_size;

		result = ioctl(fileno(stdout), TIOCGWINSZ, &screen_size);

		/* >= accounts for a one-line prompt */
		if (result == -1
			|| (lines >= screen_size.ws_row && lines >= min_lines)
			|| pager > 1)
#endif
		{
			const char *pagerprog;
			FILE	   *pagerpipe;

			pagerprog = getenv("PSQL_PAGER");
			if (!pagerprog)
				pagerprog = getenv("PAGER");
			if (!pagerprog)
				pagerprog = DEFAULT_PAGER;
			else
			{
				/* if PAGER is empty or all-white-space, don't use pager */
				if (strspn(pagerprog, " \t\r\n") == strlen(pagerprog))
					return stdout;
			}
			disable_sigpipe_trap();
			pagerpipe = popen(pagerprog, "w");
			if (pagerpipe)
				return pagerpipe;
			/* if popen fails, silently proceed without pager */
			restore_sigpipe_trap();
		}
	}

	return stdout;
}

/*
 * ClosePager