add script to update submodules (#81)

* add script to update submodules

* read from .gitmodules file

update-submodules.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+
+fail() {
+    printf '%s\n' "$1" >&2
+    exit "${2-1}"
+}
+
+# make sure we're in the root directory of the repository
+if [ ! -f "Cargo.toml" ]; then
+    fail "Failed to find \"Cargo.toml\", are you sure you're in the root directory of the repository?"
+fi
+
+cwd=$(pwd)
+
+# update all submodules
+git submodule update --init --recursive
+
+# array of submodule paths and their corresponding branch names
+submodules=()
+
+# get the path and the branch name from the .gitmodules file
+while IFS=$'\n' read -r line; do
+    if [[ "$line" =~ ^.*path\ =.*$ ]]; then
+        path=${line#*= }
+    elif [[ "$line" =~ ^.*branch\ =.*$ ]]; then
+        branch=${line#*= }
+        submodules+=("$path:$branch")
+    fi
+done < .gitmodules
+
+# iterate over the array and update each submodule
+for i in "${submodules[@]}"; do
+    name=${i%%:*}
+    branch=${i#*:}
+    echo "Updating $name to $branch"
+    # change directory to the submodule
+    cd "$name" || fail "Failed to change directory into submodule \"$name\""
+    # fetch the latest changes from the remote
+    git fetch || fail "Failed to fetch latest changes for submodule \"$name\""
+    # checkout the specified branch
+    git checkout "$branch" || fail "Failed to checkout branch \"$branch\" for submodule \"$name\""
+    # pull the latest changes from the remote
+    git pull || fail "Failed to pull latest changes for submodule \"$name\""
+    # change directory back to the root of the repository
+    cd "$cwd" || fail "Failed to change directory back to root of repository"
+done