Update HandsOn.md

workshop/HandsOn.md

@@ -311,4 +311,35 @@ singularity exec my_container.sif ls /data
 log.txt
 ```
 
+#### PATH
+Of course it is possible to modify the `PATH` that is accessible from the container.
+
+```bash
+export SINGULARITYENV_PREPEND_PATH=/opt/important/bin
+export SINGULARITYENV_APPEND_PATH=/opt/fallback/bin
+export SINGULARITYENV_PATH=/only/bin
+```
+
+#### Clean Environment
+Singularity by default exposes all environment variables from the host inside the container. Use the `--cleanenv` argument to prevent this:
+```bash
+singularity run --cleanenv <image.sif> <arg-1> <arg-2> ... <arg-N>
+```
+
+#### Setting Environment variables
+One can define an environment variable within the container as follows:
+```bash
+export SINGULARITYENV_MYVAR=Overridden
+```
+With the above definition, `MYVAR` will have the value "Overridden". 
+
+### Inspect
+
+One can sometimes learn a lot about the image by inspecting its definition file:
+
+```bash
+singularity inspect --deffile <image.sif>
+```
+
+The definition file is the recipe by which the image was made (see below). If the image was taken from Docker Hub then a definition file will not be available.