Handle empty or all-blank PAGER setting more sanely in psql.

If the PAGER environment variable is set but contains an empty string,
psql would pass it to "sh" which would silently exit, causing whatever
query output we were printing to vanish entirely.  This is quite
mystifying; it took a long time for us to figure out that this was the
cause of Joseph Brenner's trouble report.  Rather than allowing that
to happen, we should treat this as another way to specify "no pager".
(We could alternatively treat it as selecting the default pager, but
it seems more likely that the former is what the user meant to achieve
by setting PAGER this way.)

Nonempty, but all-white-space, PAGER values have the same behavior, and
it's pretty easy to test for that, so let's handle that case the same way.

Most other cases of faulty PAGER values will result in the shell printing
some kind of complaint to stderr, which should be enough to diagnose the
problem, so we don't need to work harder than this.  (Note that there's
been an intentional decision not to be very chatty about apparent failure
returns from the pager process, since that may happen if, eg, the user
quits the pager with control-C or some such.  I'd just as soon not start
splitting hairs about which exit codes might merit making our own report.)

libpq's old PQprint() function was already on board with ignoring empty
PAGER values, but for consistency, make it ignore all-white-space values
as well.

It's been like this a long time, so back-patch to all supported branches.

Discussion: https://postgr.es/m/CAFfgvXWLOE2novHzYjmQK8-J6TmHz42G8f3X0SORM44+stUGmw@mail.gmail.com

diff --git a/doc/src/sgml/ref/psql-ref.sgml b/doc/src/sgml/ref/psql-ref.sgml
index 5e4e0fd9d626dd4e5292d2854b6676513d75f31e..03f069838b00ac9a38d0d63b15ae782129fb6fbe 100644 (file)
--- a/doc/src/sgml/ref/psql-ref.sgml
+++ b/doc/src/sgml/ref/psql-ref.sgml
@@ -3354,8 +3354,9 @@ $endif
       If the query results do not fit on the screen, they are piped
       through this command.  Typical values are
       <literal>more</literal> or <literal>less</literal>.  The default
-      is platform-dependent.  The use of the pager can be disabled by
-      using the <command>\pset</command> command.
+      is platform-dependent.  Use of the pager can be disabled by setting
+      <envar>PAGER</envar> to empty, or by using pager-related options of
+      the <command>\pset</command> command.
      </para>
     </listitem>
    </varlistentry>

diff --git a/src/bin/psql/print.c b/src/bin/psql/print.c
index 12a5421f1e34d577e3c1da1506b9cbea54f51bb0..bf5f4ff567118316ef509fab4ae276a2fd1de82c 100644 (file)
--- a/src/bin/psql/print.c
+++ b/src/bin/psql/print.c
@@ -2075,6 +2075,12 @@ PageOutput(int lines, unsigned short int pager)
            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;
+           }
 #ifndef WIN32
            pqsignal(SIGPIPE, SIG_IGN);
 #endif

diff --git a/src/interfaces/libpq/fe-print.c b/src/interfaces/libpq/fe-print.c
index 585e831cdb6fbce5e40a2b1f88b97c15a7737963..cb360c36a1876470a44e94f8526ebd12e69eeb9c 100644 (file)
--- a/src/interfaces/libpq/fe-print.c
+++ b/src/interfaces/libpq/fe-print.c
@@ -167,8 +167,9 @@ PQprint(FILE *fout, const PGresult *res, const PQprintOpt *po)
            screen_size.ws_col = 80;
 #endif
            pagerenv = getenv("PAGER");
+           /* if PAGER is unset, empty or all-white-space, don't use pager */
            if (pagerenv != NULL &&
-               pagerenv[0] != '\0' &&
+               strspn(pagerenv, " \t\r\n") != strlen(pagerenv) &&
                !po->html3 &&
                ((po->expanded &&
                  nTups * (nFields + 1) >= screen_size.ws_row) ||