Use the status command in the package REPL mode to see which packages have already been installed:

It is advisable to regularly (and certainly before installing a new package) execute the up command to ensure that your local package repository is up-to-date and synchronized, as shown in the following screenshot:

If you only want to update one package, specify the package name after the up command.

The rm command is used for deleting a package, but it removes only the reference to it. To completely remove the sources, use the gc command.

As we saw in Chapter 1, Installing the Julia Platform, packages are installed via add PackageName and brought into scope using PackageName. You can also clone a package from a git repository as follows:

Pkg.clone("[email protected]:ericchiang/ANN.jl.git")

If you need to force a certain package to a certain version (perhaps an older version), use pin. For example, use pin HDF5, v"0.4.3" to force the use of version 0.4.3 of package HDF5, even when you already have version 0.4.4 installed.