Add warnings to use php_sapi_name() to test when running as CLI (#4337)

Author: jimwins

features/commandline.xml

@@ -182,6 +182,27 @@
            also be found in the <varname>$_SERVER</varname> array, for example:
            <varname>$_SERVER['argv']</varname>.
           </para>
+          <warning>
+           <para>
+            The presence of <varname>$argv</varname> or <varname>$_SERVER['argv']</varname>
+            is not a reliable indication that a script is being run from the
+            command line because they may be set in other contexts when
+            <link linkend="ini.register-argc-argv">register_argc_argv</link> is enabled.
+            The value returned by <function>php_sapi_name</function> should be checked
+            instead.
+            <informalexample>
+             <programlisting role="php">
+<![CDATA[
+<?php
+
+if (php_sapi_name() === 'cli') {
+    echo "This is being run from the command line!\n";
+}
+]]>
+             </programlisting>
+            </informalexample>
+           </para>
+          </warning>
           </entry>
          </row>
          <row>

language/predefined/variables/argv.xml

@@ -25,6 +25,14 @@
     is disabled.
    </simpara>
   </note>
+  <warning>
+   <simpara>
+    To test if a script is being run from the command
+    line, <function>php_sapi_name</function> should be used
+    instead of checking whether <varname>$argv</varname> or
+    <varname>$_SERVER['argv']</varname> is set.
+   </simpara>
+  </warning>
  </refsect1>
 
  <refsect1 role="examples">