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--- cookbooks:devel:core [2022/02/14 07:49] – [tcp_script_mode] miconda
+++ cookbooks:devel:core [2022/04/11 15:10] (current) – [substdefs] bkaufman
@@ Line 439: / Line 439: @@
 Similar to **subst**, but in addition it adds a **#!define ID "subst"** (note the difference from #!substdef that the value for define is enclosed in double quotes, useful when the define is used in a place for a string value).
+==== trydefenv ====
+<code c>
+#!trydefenv ID=ENVVAR
+</code>
+Similar to **defenv**, but will not error if the environmental variable is not set.  This allows for boolean defines via system ENVVARs.  For example, using an environmental variable to toggle loading of db_mysql:
+<code c>
+#!trydefenv WITH_MYSQL
+#!ifdef WITH_MYSQL
+loadmodule "db_mysql.so"
+#!ifdef
+</code>
+==== trydefenvns ====
+Similar to **#!trydefenv**, but the value is defined in between double quotes to make it convenient to be used as a string token.
+<code c>
+#!trydefenvs ENVVAR
+#!trydefenvs ID=ENVVAR
+</code>
 ===== Core Keywords =====