adding mkdocs

docs/howto/append.md

@@ -0,0 +1,31 @@
+Sometimes it might be useful to be able to append some text to a 
+file. Dotdrop is able to do that with the help of
+[actions](https://github.com/deadc0de6/dotdrop/wiki/usage-actions)
+and a temporary file.
+
+Below is a config example to append to a file:
+```yaml
+dynvariables:
+  tmpfile: mktemp
+variables:
+  somefile_final: ~/.somefile
+dotfiles:
+  f_somefile:
+    dst: "{{@@ tmpfile @@}}"
+    src: somefile
+    actions:
+      - strip "{{@@ somefile_final @@}}"
+      - append "{{@@ tmpfile @@}}" "{{@@ somefile_final @@}}"
+actions:
+  pre:
+    strip: "sed -i '/^# my pattern$/,$d' {0}"    
+  post:
+    append: "cat {0} >> {1}; rm -f {0}"
+```
+During installation, the `strip` action is executed before the installation and strips everything from the pattern `# my pattern` to the end of the file. Then the dotfile `somefile` is installed in a temporary location (here `tmpfile`) and finally the post action `append` will append the content of the `tmpfile` to the final dotfile pointed by `somefile_final`
+
+Obviously the dotfile in the dotpath should start with a unique pattern (here `# my pattern`):
+```
+# my pattern
+this is the end
+```