Add CLI command to enter environment

mcli

 #!/usr/bin/env bash
 
-MACAO_ROOT="${MACAO_ROOT:-$(dirname "$0")}"
-SOURCES_DIR="$MACAO_ROOT/Basilisk/MACAO/macao_12"
-SCRIPTS_DIR="$MACAO_ROOT/tetras_extraction/macao_12/script"
-RESULTS_DIR="$MACAO_ROOT/tetras_extraction/macao_12/result"
+export MACAO_ROOT="${MACAO_ROOT:-$(dirname "$0")}"
+export SOURCES_DIR="$MACAO_ROOT/Basilisk/MACAO/macao_12"
+export SCRIPTS_DIR="$MACAO_ROOT/tetras_extraction/macao_12/script"
+export RESULTS_DIR="$MACAO_ROOT/tetras_extraction/macao_12/result"
 
 print_usage() {
     cat <<EOF
@@ -23,6 +23,9 @@ extract-rdf
     Run the extractor to generate RDF from text sources
 extract-mp3
     Extract audio streams from all Flash SWF files
+shell [-p|--pyenv]
+    Open a shell with mcli's environment variables set, including PATH.
+    If -p or --pyenv is specified, also enter the Python virtual env.
 help
     Print this help and exit
 EOF
@@ -102,6 +105,17 @@ extract-mp3)
         "$SCRIPTS_DIR/extract_mp3.sh" --output-dir "$RESULTS_DIR/audio" "$audio_file"
     done
     ;;
+shell)
+    export PATH="$PATH:$MACAO_ROOT"
+    if [[ "$1" = "-p" || "$1" = "--pyenv" ]]; then
+        if ! source "$SCRIPTS_DIR/venv/bin/activate"; then
+            echo "Python venv not found, did you run setup first?" >&2
+            exit 1
+        fi
+    fi
+    cd "$MACAO_ROOT"
+    $SHELL
+    ;;
 *)
     print_usage
     ;;