systemctl: Add SYSTEMD_PAGER for setting the pager to use in systemctl

man/systemctl.xml

@@ -1021,6 +1021,22 @@
                 code otherwise.</para>
         </refsect1>
 
+        <refsect1>
+                <title>Environment</title>
+
+                <variablelist>
+                        <varlistentry>
+                                <term><varname>$SYSTEMD_PAGER</varname></term>
+                                <listitem><para>Pager to use when
+                                <option>--no-pager</option> is not given;
+                                overrides <varname>$PAGER</varname>.  Setting
+                                this to an empty string or the value
+                                <literal>cat</literal> is equivalent to passing
+                                <option>--no-pager</option>.</para></listitem>
+                        </varlistentry>
+                </variablelist>
+        </refsect1>
+
         <refsect1>
                 <title>See Also</title>
                 <para>

src/systemctl.c

@@ -5572,7 +5572,7 @@ static void pager_open(void) {
         if (!on_tty() || arg_no_pager)
                 return;
 
-        if ((pager = getenv("PAGER")))
+        if ((pager = getenv("SYSTEMD_PAGER")) || (pager = getenv("PAGER")))
                 if (!*pager || streq(pager, "cat"))
                         return;