examples: improve shell session usability

- Add usage prompt when starting shell sessions

- Give all examples an uniform interface ("c") for running commands
  or starting a shell on the node.

examples/deploy-container.sh

@@ -62,7 +62,13 @@ in {
 }
 EOF
 # Run command in container
-c() { sudo extra-container run demo-node -- "$@" | cat; }
+c() {
+    if [[ $# > 0 ]]; then
+        sudo extra-container run demo-node -- "$@" | cat;
+    else
+        sudo nixos-container root-login demo-node
+    fi
+}
 
 echo
 echo "Bitcoind service:"

examples/deploy-nixops.sh

@@ -38,6 +38,7 @@ nixops deploy -d bitcoin-node
 # Connect to node
 nixops ssh bitcoin-node systemctl status bitcoind
 
+c() { nixops ssh bitcoin-node "$@"; }
 # Uncomment to start a shell session here
 # . start-bash-session.sh
 

examples/start-bash-session.sh

@@ -1,6 +1,15 @@
 # Start an interactive bash session in the current bash environment.
 
+USAGE_INFO='
+Starting shell...
+Run "c COMMAND" to execute a command on the bitcoin node
+Run "c" to start a shell session inside the node'
+
 # BASH_ENVIRONMENT contains definitions of read-only variables like 'BASHOPTS' that
-# cause warnings on importing. Suppress these warnings during bash startup.
+# cause warnings on evaluation. Suppress these warnings while sourcing.
 BASH_ENVIRONMENT=<(declare -p; declare -pf) \
-  bash --rcfile <(echo 'source $BASH_ENVIRONMENT 2>/dev/null')
+USAGE_INFO="$USAGE_INFO" \
+  bash --rcfile <(echo '
+    source $BASH_ENVIRONMENT 2>/dev/null
+    echo "$USAGE_INFO"
+  ')