Tighten usage of PSQL_WATCH_PAGER.

Don't use PSQL_WATCH_PAGER when stdin/stdout are not a terminal.
This corresponds to the restrictions on when other commands will
use [PSQL_]PAGER.  There isn't a lot of sense in trying to use a
pager in non-interactive cases, and doing so allows an environment
setting to break our tests.

Also, ignore PSQL_WATCH_PAGER if it is set but empty or all-blank,
for the same reasons we ignore such settings of [PSQL_]PAGER (see
commit 18f8f784c).

No documentation change is really needed, since there is nothing
suggesting that these constraints on [PSQL_]PAGER didn't already
apply to PSQL_WATCH_PAGER too.  But I rearranged the text
a little to make it read more naturally (IMHO anyway).

Per report from Pavel Stehule.  Back-patch to v15 where
PSQL_WATCH_PAGER was introduced.

Discussion: https://postgr.es/m/CAFj8pRDTwFzmEWdA-gdAcUh0ZnxUioSfTMre71WyB_wNJy-8gw@mail.gmail.com

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index dc422373d6ff4034954db714cd13734708447689..de760f99909d958d3b7605b1bf1d9cce0ced540a 100644 (file)
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -3120,8 +3120,21 @@ lo_import 152801
           
           
           Controls use of a pager program for query and psql
-          help output.  If the environment variable PSQL_PAGER
-          or PAGER is set, the output is piped to the
+          help output.
+          When the pager option is off, the pager
+          program is not used. When the pager option is
+          on, the pager is used when appropriate, i.e., when the
+          output is to a terminal and will not fit on the screen.
+          The pager option can also be set to always,
+          which causes the pager to be used for all terminal output regardless
+          of whether it fits on the screen.  \pset pager
+          without a value
+          toggles pager use on and off.
+          
+
+          
+          If the environment variable PSQL_PAGER
+          or PAGER is set, output to be paged is piped to the
           specified program.  Otherwise a platform-dependent default program
           (such as more) is used.
           
@@ -3135,18 +3148,6 @@ lo_import 152801
           psql's output format (such as
           pspg --stream).
           
-
-          
-          When the pager option is off, the pager
-          program is not used. When the pager option is
-          on, the pager is used when appropriate, i.e., when the
-          output is to a terminal and will not fit on the screen.
-          The pager option can also be set to always,
-          which causes the pager to be used for all terminal output regardless
-          of whether it fits on the screen.  \pset pager
-          without a value
-          toggles pager use on and off.
-          
           
           
 
@@ -4898,7 +4899,7 @@ PSQL_EDITOR_LINENUMBER_ARG='--line '
       pager-related options of the \pset command.
       These variables are examined in the order listed;
       the first that is set is used.
-      If none of them is set, the default is to use more on most
+      If neither of them is set, the default is to use more on most
       platforms, but less on Cygwin.
      
 

diff --git a/src/bin/psql/command.c b/src/bin/psql/command.c
index 97f7d972202b6033384722071be27380605bdd0c..607a57715a32ba30a166f667523cf857177cdaa8 100644 (file)
--- a/src/bin/psql/command.c
+++ b/src/bin/psql/command.c
@@ -5197,14 +5197,20 @@ do_watch(PQExpBuffer query_buf, double sleep, int iter)
 
    /*
     * For \watch, we ignore the size of the result and always use the pager
-    * if PSQL_WATCH_PAGER is set.  We also ignore the regular PSQL_PAGER or
-    * PAGER environment variables, because traditional pagers probably won't
-    * be very useful for showing a stream of results.
+    * as long as we're talking to a terminal and "\pset pager" is enabled.
+    * However, we'll only use the pager identified by PSQL_WATCH_PAGER.  We
+    * ignore the regular PSQL_PAGER or PAGER environment variables, because
+    * traditional pagers probably won't be very useful for showing a stream
+    * of results.
     */
 #ifndef WIN32
    pagerprog = getenv("PSQL_WATCH_PAGER");
+   /* if variable is empty or all-white-space, don't use pager */
+   if (pagerprog && strspn(pagerprog, " \t\r\n") == strlen(pagerprog))
+       pagerprog = NULL;
 #endif
-   if (pagerprog && myopt.topt.pager)
+   if (pagerprog && myopt.topt.pager &&
+       isatty(fileno(stdin)) && isatty(fileno(stdout)))
    {
        fflush(NULL);
        disable_sigpipe_trap();