Add a pager_min_lines setting to psql

If set, the pager will not be used unless this many lines are to be
displayed, even if that is more than the screen depth. Default is zero,
meaning it's disabled.

There is probably more work to be done in giving the user control over
when the pager is used, particularly when wide output forces use of the
pager regardless of how many lines there are, but this is a start.

Author: adunstan

doc/src/sgml/ref/psql-ref.sgml

@@ -2235,6 +2235,18 @@ lo_import 152801
           </listitem>
           </varlistentry>
 
+          <varlistentry>
+          <term><literal>pager_min_lines</literal></term>
+          <listitem>
+          <para>
+          If <literal>pager_min_lines</> is set to a number greater than the
+          page height, the pager program will not be called unless there are
+          at least this many lines of output to show. The default setting
+          is 0.
+          </para>
+          </listitem>
+          </varlistentry>
+
           <varlistentry>
           <term><literal>recordsep</literal></term>
           <listitem>

src/bin/psql/command.c

@@ -1071,7 +1071,8 @@ exec_command(const char *cmd,
 			static const char *const my_list[] = {
 				"border", "columns", "expanded", "fieldsep", "fieldsep_zero",
 				"footer", "format", "linestyle", "null",
-				"numericlocale", "pager", "recordsep", "recordsep_zero",
+				"numericlocale", "pager", "pager_min_lines",
+				"recordsep", "recordsep_zero",
 				"tableattr", "title", "tuples_only",
 				"unicode_border_linestyle",
 				"unicode_column_linestyle",
@@ -1265,7 +1266,7 @@ exec_command(const char *cmd,
 					lines++;
 				}
 
-				output = PageOutput(lineno, pset.popt.topt.pager);
+				output = PageOutput(lineno, &(pset.popt.topt));
 				is_pager = true;
 			}
 			else
@@ -2519,6 +2520,13 @@ do_pset(const char *param, const char *value, printQueryOpt *popt, bool quiet)
 			popt->topt.pager = 1;
 	}
 
+	/* set minimum lines for pager use */
+	else if (strcmp(param, "pager_min_lines") == 0)
+	{
+		if (value)
+			popt->topt.pager_min_lines = atoi(value);
+	}
+
 	/* disable "(x rows)" footer */
 	else if (strcmp(param, "footer") == 0)
 	{
@@ -2640,6 +2648,13 @@ printPsetInfo(const char *param, struct printQueryOpt *popt)
 			printf(_("Pager usage is off.\n"));
 	}
 
+	/* show minimum lines for pager use */
+	else if (strcmp(param, "pager_min_lines") == 0)
+	{
+		printf(_("Pager won't be used for less than %d lines\n"),
+			   popt->topt.pager_min_lines);
+	}
+
 	/* show record separator for unaligned text */
 	else if (strcmp(param, "recordsep") == 0)
 	{
@@ -2792,6 +2807,8 @@ pset_value_string(const char *param, struct printQueryOpt *popt)
 		return pstrdup(pset_bool_string(popt->topt.numericLocale));
 	else if (strcmp(param, "pager") == 0)
 		return psprintf("%d", popt->topt.pager);
+	else if (strcmp(param, "pager_min_lines") == 0)
+		return psprintf("%d", popt->topt.pager_min_lines);
 	else if (strcmp(param, "recordsep") == 0)
 		return pset_quoted_string(popt->topt.recordSep.separator
 								  ? popt->topt.recordSep.separator

src/bin/psql/common.c

@@ -1337,7 +1337,7 @@ ExecQueryUsingCursor(const char *query, double *elapsed_msec)
 			 * If query requires multiple result sets, hack to ensure that
 			 * only one pager instance is used for the whole mess
 			 */
-			pset.queryFout = PageOutput(100000, my_popt.topt.pager);
+			pset.queryFout = PageOutput(100000, &(my_popt.topt));
 			did_pager = true;
 		}
 

src/bin/psql/help.c

@@ -65,7 +65,7 @@ usage(unsigned short int pager)
 		}
 	}
 
-	output = PageOutput(59, pager);
+	output = PageOutput(59, pager ? &(pset.popt.topt) : NULL);
 
 	fprintf(output, _("psql is the PostgreSQL interactive terminal.\n\n"));
 	fprintf(output, _("Usage:\n"));
@@ -158,7 +158,7 @@ slashUsage(unsigned short int pager)
 
 	currdb = PQdb(pset.db);
 
-	output = PageOutput(103, pager);
+	output = PageOutput(103, pager ? &(pset.popt.topt) : NULL);
 
 	/* if you add/remove a line here, change the row count above */
 
@@ -305,7 +305,7 @@ helpVariables(unsigned short int pager)
 {
 	FILE	   *output;
 
-	output = PageOutput(85, pager);
+	output = PageOutput(85, pager ? &(pset.popt.topt) : NULL);
 
 	fprintf(output, _("List of specially treated variables.\n"));
 
@@ -435,7 +435,7 @@ helpSQL(const char *topic, unsigned short int pager)
 		ncolumns = Max(ncolumns, 1);
 		nrows = (QL_HELP_COUNT + (ncolumns - 1)) / ncolumns;
 
-		output = PageOutput(nrows + 1, pager);
+		output = PageOutput(nrows + 1, pager ? &(pset.popt.topt) : NULL);
 
 		fputs(_("Available help:\n"), output);
 
@@ -488,7 +488,7 @@ helpSQL(const char *topic, unsigned short int pager)
 				if (wordlen >= len)		/* Don't try again if the same word */
 				{
 					if (!output)
-						output = PageOutput(nl_count, pager);
+						output = PageOutput(nl_count, pager ? &(pset.popt.topt) : NULL);
 					break;
 				}
 				len = wordlen;
@@ -509,7 +509,7 @@ helpSQL(const char *topic, unsigned short int pager)
 			}
 
 			if (!output)
-				output = PageOutput(nl_count, pager);
+				output = PageOutput(nl_count, pager ? &(pset.popt.topt) : NULL);
 
 			for (i = 0; QL_HELP[i].cmd; i++)
 			{

src/bin/psql/input.c

@@ -474,7 +474,7 @@ printHistory(const char *fname, unsigned short int pager)
 	if (fname == NULL)
 	{
 		/* use pager, if enabled, when printing to console */
-		output = PageOutput(INT_MAX, pager);
+		output = PageOutput(INT_MAX, pager ? &(pset.popt.topt) : NULL);
 		is_pager = true;
 	}
 	else

src/bin/psql/print.c

@@ -811,7 +811,7 @@ print_aligned_text(const printTableContent *cont, FILE *fout)
 	if (!is_pager && fout == stdout && output_columns > 0 &&
 		(output_columns < total_header_width || output_columns < width_total))
 	{
-		fout = PageOutput(INT_MAX, cont->opt->pager);	/* force pager */
+		fout = PageOutput(INT_MAX, cont->opt);	/* force pager */
 		is_pager = true;
 	}
 
@@ -2497,15 +2497,19 @@ print_troff_ms_vertical(const printTableContent *cont, FILE *fout)
  * PageOutput
  *
  * Tests if pager is needed and returns appropriate FILE pointer.
+ *
+ * If the topt argument is NULL no pager is used.
  */
 FILE *
-PageOutput(int lines, unsigned short int pager)
+PageOutput(int lines, const printTableOpt *topt)
 {
 	/* check whether we need / can / are supposed to use pager */
-	if (pager && isatty(fileno(stdin)) && isatty(fileno(stdout)))
+	if (topt && topt->pager && isatty(fileno(stdin)) && isatty(fileno(stdout)))
 	{
 		const char *pagerprog;
 		FILE	   *pagerpipe;
+		unsigned short int  pager =  topt->pager;
+		int         min_lines = topt->pager_min_lines;
 
 #ifdef TIOCGWINSZ
 		int			result;
@@ -2514,7 +2518,9 @@ PageOutput(int lines, unsigned short int pager)
 		result = ioctl(fileno(stdout), TIOCGWINSZ, &screen_size);
 
 		/* >= accounts for a one-line prompt */
-		if (result == -1 || lines >= screen_size.ws_row || pager > 1)
+		if (result == -1
+			|| (lines >= screen_size.ws_row && lines >= min_lines)
+			|| pager > 1)
 		{
 #endif
 			pagerprog = getenv("PAGER");
@@ -2814,7 +2820,7 @@ IsPagerNeeded(const printTableContent *cont, const int extra_lines, bool expande
 				lines++;
 		}
 
-		*fout = PageOutput(lines + extra_lines, cont->opt->pager);
+		*fout = PageOutput(lines + extra_lines, cont->opt);
 		*is_pager = (*fout != stdout);
 	}
 	else

src/bin/psql/print.h

@@ -89,6 +89,8 @@ typedef struct printTableOpt
 								 * 1=dividing lines, 2=full */
 	unsigned short int pager;	/* use pager for output (if to stdout and
 								 * stdout is a tty) 0=off 1=on 2=always */
+	int         pager_min_lines;/* don't use pager unless there are at least
+								 * this many lines */
 	bool		tuples_only;	/* don't output headers, row counts, etc. */
 	bool		start_table;	/* print start decoration, eg <table> */
 	bool		stop_table;		/* print stop decoration, eg </table> */
@@ -164,7 +166,7 @@ extern const printTextFormat pg_asciiformat_old;
 extern const printTextFormat pg_utf8format;
 
 
-extern FILE *PageOutput(int lines, unsigned short int pager);
+extern FILE *PageOutput(int lines, const printTableOpt *topt);
 extern void ClosePager(FILE *pagerpipe);
 
 extern void html_escaped_print(const char *in, FILE *fout);

src/bin/psql/startup.c

@@ -129,6 +129,7 @@ main(int argc, char *argv[])
 	pset.popt.topt.format = PRINT_ALIGNED;
 	pset.popt.topt.border = 1;
 	pset.popt.topt.pager = 1;
+	pset.popt.topt.pager_min_lines = 0;
 	pset.popt.topt.start_table = true;
 	pset.popt.topt.stop_table = true;
 	pset.popt.topt.default_footer = true;

src/test/regress/expected/psql.out

@@ -65,6 +65,7 @@ linestyle                ascii
 null                     ''
 numericlocale            off
 pager                    1
+pager_min_lines          0
 recordsep                '\n'
 recordsep_zero           off
 tableattr