diff --git a/README.md b/README.md
old mode 100755
new mode 100644
diff --git a/download.sh b/download.sh
old mode 100644
new mode 100755
index 8cfed9935..88ae83530
--- a/download.sh
+++ b/download.sh
@@ -3,58 +3,112 @@
 # Copyright (c) Meta Platforms, Inc. and affiliates.
 # This software may be used and distributed according to the terms of the Llama 2 Community License Agreement.
 
-read -p "Enter the URL from email: " PRESIGNED_URL
-echo ""
-read -p "Enter the list of models to download without spaces (7B,13B,70B,7B-chat,13B-chat,70B-chat), or press Enter for all: " MODEL_SIZE
+PRESIGNED_URL=""              # URL from email
 TARGET_FOLDER="."             # where all files should end up
-mkdir -p ${TARGET_FOLDER}
+
+# Download a file from the presigned URL, saving it to the target folder.
+# Resumes downloading partially downloaded files.
+# $1 - partial path of file to download
+# $2 - target folder
+download () {
+    local filename="$1"
+    local target_dir="$2"
+    [[ -d "$target_dir" ]] || mkdir -p "$target_dir"
+    wget --continue "${PRESIGNED_URL/'*'/"$filename"}" -O "${target_dir}/${filename}"
+}
+
+# $1 - checklist file
+md5check () {
+    if [[ ! -f "$1" ]]; then
+        echo "Missing checklist file: $1" >&2
+        return 1
+    fi
+    if [[ "$OSTYPE" == "darwin"* ]]; then
+        failed=0
+        while read -r hash file; do
+            if [[ -n "$hash" ]]; then
+                printf "%s: " "$file"
+                if [[ "$(md5 -q "$file")" != "$hash" ]]; then
+                    echo "FAILED"
+                    (( failed++ ))
+                else
+                    echo "OK"
+                fi
+            fi
+        done < "$1"
+        if (( failed > 0 )); then
+            echo "$failed files failed checksum" >&2
+            return 1
+        else
+            return 0
+        fi
+    else
+        md5sum -c "$1"
+        return $?
+    fi
+}
+
+# If the user didn't modify the script to include the URL, ask for it
+if [[ -z "$PRESIGNED_URL" ]]; then
+    read -p "Enter the URL from email: " PRESIGNED_URL
+    echo ""
+fi
+
+# Check if the PRESIGNED_URL has the form `https://..*...` (i.e. with one wildcard '*' in the path)
+if ! echo "$PRESIGNED_URL" | grep -q -E '^https://[^*]+[*][^*]*'; then
+    echo "Invalid URL: $PRESIGNED_URL" >&2
+    echo "Expected: The URL from the email, containing one asterisk '*'." >&2
+    exit 1
+fi
+
+ALL_MODELS="7B,13B,70B,7B-chat,13B-chat,70B-chat"
+read -p "Enter the list of models to download without spaces (${ALL_MODELS}), or press Enter for all: " MODEL_SIZE
 
 if [[ $MODEL_SIZE == "" ]]; then
-    MODEL_SIZE="7B,13B,70B,7B-chat,13B-chat,70B-chat"
+    MODEL_SIZE="$ALL_MODELS"
 fi
 
+mkdir -p "$TARGET_FOLDER"
+
 echo "Downloading LICENSE and Acceptable Usage Policy"
-wget ${PRESIGNED_URL/'*'/"LICENSE"} -O ${TARGET_FOLDER}"/LICENSE"
-wget ${PRESIGNED_URL/'*'/"USE_POLICY.md"} -O ${TARGET_FOLDER}"/USE_POLICY.md"
+download "LICENSE" "$TARGET_FOLDER"
+download "USE_POLICY.md" "$TARGET_FOLDER"
 
 echo "Downloading tokenizer"
-wget ${PRESIGNED_URL/'*'/"tokenizer.model"} -O ${TARGET_FOLDER}"/tokenizer.model"
-wget ${PRESIGNED_URL/'*'/"tokenizer_checklist.chk"} -O ${TARGET_FOLDER}"/tokenizer_checklist.chk"
-(cd ${TARGET_FOLDER} && md5sum -c tokenizer_checklist.chk)
-
-for m in ${MODEL_SIZE//,/ }
-do
-    if [[ $m == "7B" ]]; then
-        SHARD=0
-        MODEL_PATH="llama-2-7b"
-    elif [[ $m == "7B-chat" ]]; then
-        SHARD=0
-        MODEL_PATH="llama-2-7b-chat"
-    elif [[ $m == "13B" ]]; then
-        SHARD=1
-        MODEL_PATH="llama-2-13b"
-    elif [[ $m == "13B-chat" ]]; then
-        SHARD=1
-        MODEL_PATH="llama-2-13b-chat"
-    elif [[ $m == "70B" ]]; then
-        SHARD=7
-        MODEL_PATH="llama-2-70b"
-    elif [[ $m == "70B-chat" ]]; then
-        SHARD=7
-        MODEL_PATH="llama-2-70b-chat"
-    fi
+download "tokenizer.model" "$TARGET_FOLDER"
+download "tokenizer_checklist.chk" "$TARGET_FOLDER"
+(cd "$TARGET_FOLDER" && md5check tokenizer_checklist.chk)
+
+for m in ${MODEL_SIZE//,/ }; do
+    case $m in
+        "7B")
+            SHARD=0; MODEL_PATH="llama-2-7b" ;;
+        "7B-chat")
+            SHARD=0; MODEL_PATH="llama-2-7b-chat" ;;
+        "13B")
+            SHARD=1; MODEL_PATH="llama-2-13b" ;;
+        "13B-chat")
+            SHARD=1; MODEL_PATH="llama-2-13b-chat" ;;
+        "70B")
+            SHARD=7; MODEL_PATH="llama-2-70b" ;;
+        "70B-chat")
+            SHARD=7; MODEL_PATH="llama-2-70b-chat" ;;
+        *)
+            echo "Invalid model size: $m" >&2
+            echo "Expected: one of $ALL_MODELS" >&2
+            continue
+            ;;
+    esac
 
-    echo "Downloading ${MODEL_PATH}"
-    mkdir -p ${TARGET_FOLDER}"/${MODEL_PATH}"
+    echo "Downloading $MODEL_PATH"
+    mkdir -p "${TARGET_FOLDER}/${MODEL_PATH}"
 
-    for s in $(seq -f "0%g" 0 ${SHARD})
-    do
-        wget ${PRESIGNED_URL/'*'/"${MODEL_PATH}/consolidated.${s}.pth"} -O ${TARGET_FOLDER}"/${MODEL_PATH}/consolidated.${s}.pth"
+    for s in $(seq -f "0%g" 0 ${SHARD}); do
+        download "${MODEL_PATH}/consolidated.${s}.pth" "$TARGET_FOLDER"
     done
 
-    wget ${PRESIGNED_URL/'*'/"${MODEL_PATH}/params.json"} -O ${TARGET_FOLDER}"/${MODEL_PATH}/params.json"
-    wget ${PRESIGNED_URL/'*'/"${MODEL_PATH}/checklist.chk"} -O ${TARGET_FOLDER}"/${MODEL_PATH}/checklist.chk"
+    download "${MODEL_PATH}/params.json" "$TARGET_FOLDER"
+    download "${MODEL_PATH}/checklist.chk" "$TARGET_FOLDER"
     echo "Checking checksums"
-    (cd ${TARGET_FOLDER}"/${MODEL_PATH}" && md5sum -c checklist.chk)
+    (cd "${TARGET_FOLDER}/${MODEL_PATH}" && md5check checklist.chk)
 done
-
diff --git a/example_chat_completion.py b/example_chat_completion.py
old mode 100644
new mode 100755