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-rw-r--r--doc/guix.texi20
1 files changed, 20 insertions, 0 deletions
diff --git a/doc/guix.texi b/doc/guix.texi
index ab1e4be20f..f7adfafe54 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -5543,6 +5543,26 @@ editor, @command{find}, @command{grep}, etc. The example above adds
tcpdump to those, taken from the @code{(gnu packages admin)} module
(@pxref{Package Modules}).
+@findex specification->package
+Referring to packages by variable name, like @var{tcpdump} above, has
+the advantage of being unambiguous; it also allows typos and such to be
+diagnosed right away as ``unbound variables''. The downside is that one
+needs to know which module defines which package, and to augment the
+@code{use-package-modules} line accordingly. To avoid that, one can use
+the @code{specification->package} procedure of the @code{(gnu packages)}
+module, which returns the best package for a given name or name and
+version:
+
+@lisp
+(use-modules (gnu packages))
+
+(operating-system
+ ;; ...
+ (packages (append (map specification->package
+ '("tcpdump" "htop" "gnupg-2.0"))
+ %base-packages)))
+@end lisp
+
@vindex %base-services
The @code{services} field lists @dfn{system services} to be made
available when the system starts (@pxref{Services}).