As it was pointed out in #1636229 by Michael Hall (mhall119) it should be "snap run --shell <command name>" not <snap name>.
For example:
$ snap run --shell postgresql93.psql
which works for me.
As it was pointed out in #1636229 by Michael Hall (mhall119) it should be "snap run --shell <command name>" not <snap name>.
For example:
$ snap run --shell postgresql93.psql
which works for me.