add download script

Author: FGasper

README.md

@@ -22,6 +22,12 @@ Once downloaded, you will have to extract the binary and add it to your PATH
 variable. For detailed instructions for each of our supported platforms, please visit
 [installation documentation](https://www.mongodb.com/docs/mongodb-shell/install#mdb-shell-install).
 
+You can also run `download_latest.sh` to download a `mongosh` binary. You can use
+this script without cloning the repository thus:
+```
+curl -sSL https://raw.githubusercontent.com/mongodb-js/mongosh/refs/heads/main/download_latest.sh | sh
+```
+
 ## CLI Usage
 
 <!-- AUTOMATICALLY_INSERT_CLI_USAGE -->

download_latest.sh

@@ -0,0 +1,74 @@
+#!/bin/sh
+
+set -o errexit
+
+for tool in jq curl; do
+    which "$tool" >/dev/null || {
+        echo >&2 "This script requires '$tool'."
+        exit 1
+    }
+done
+
+os=$(uname -o | tr '[:upper:]' '[:lower:]')
+arch=$(uname -m)
+
+case "$os" in
+    *linux)
+        ext=tgz
+        os=linux
+        ;;
+    darwin)
+        ext=zip
+        ;;
+    *)
+        echo >&2 "This script does not support this OS ($os). Download mongosh manually."
+        exit 1
+esac
+
+case "$arch" in
+    amd64|x86_64)
+        arch=x64
+        ;;
+    aarch64)
+        arch=arm64
+esac
+
+urls=$(curl -fsSL https://api.github.com/repos/mongodb-js/mongosh/releases/latest | jq -r '.assets[] | .browser_download_url' | grep -v -e \.sig -e shared -e openssl)
+url=$(printf "%s" "$urls" | grep "\-${os}-${arch}" ||:)
+
+if [ -z "$url" ]; then
+    cat <<EOL
+No download found for $os on $arch; download manually.
+
+URLs considered:
+$urls
+EOL
+    exit 1
+fi
+
+case "$ext" in
+    zip)
+        file=$(mktemp)
+
+        echo "Downloading $url to $file …"
+        trap 'rm -f $file' EXIT
+
+        curl -fsSL "$url" > "$file"
+        echo "Downloaded $ext file; extracting mongosh …"
+
+        unzip -j "$file" '*/mongosh'
+        ;;
+    tgz)
+        echo "Downloading & extracting from $url …"
+
+        curl -fsSL "$url" | tar -xzf - \
+            --transform "s/.*\///" \
+            --wildcards "**/mongosh"
+
+        ;;
+    *)
+        echo >&2 "Bad file extension: $ext"
+        exit 1
+esac
+
+echo "Success! 'mongosh' is now saved in this directory."