add submodule revision change helper script

README.md

@@ -73,3 +73,20 @@ The GitHub organizations of submodule repositories are:
 - https://github.com/strict-types
 - https://github.com/rust-amplify
 - https://github.com/UBIDECO
+
+## Contribute
+
+### Submodule revision change helper
+A helper to change the revision for all submodules is available in the form of
+the `sub-rev-change.sh` script.
+
+As an example, it can be used to update all submodules to the `master` branch
+with:
+```sh
+./sub-rev-change.sh --branch master
+```
+
+See the help for more details on its usage:
+```sh
+./sub-rev-change.sh --help
+```

sub-rev-change.sh

@@ -0,0 +1,147 @@
+#!/usr/bin/env bash
+#
+# change all submodules in the current project to the requested branch or tag
+#
+# optionally use the specified remote where the branch or tag are to be found
+# optionally fetch the specified remote, or all if none was specified
+#
+# if the specified parameters are invalid (e.g. the branch doesn't exist),
+# nothing is done and execution continues to the next submodule
+
+# colors
+NC='\033[0m'        # no color
+BLUE='\033[0;34m'   # blue
+GREEN='\033[0;32m'  # green
+ORANGE='\033[0;33m' # orange
+RED='\033[0;31m'    # red
+
+# vars
+BRANCH=""                           # branch to change to
+DIR="$(realpath "$(dirname "$0")")" # script path
+FETCH=0                             # don't fetch by default
+REMOTE=""                           # remote where to look for revs
+TAG=""                              # tag to change to
+
+# helper functions
+_die() {
+    printf "\n${RED}ERROR: %s${NC}\n" "$@"
+    exit 1
+}
+
+_head() {
+    printf "${GREEN}%s${NC}\n" "$@"
+}
+
+_log() {
+    printf "${BLUE}%s${NC}\n" "$@"
+}
+
+_war() {
+    printf "${ORANGE}WARNING: %s${NC}\n" "$@"
+}
+
+# CLI handling
+help() {
+    echo "$0 [-h] [-f] [-r <remote>] (-b) <branch>"
+    echo ""
+    echo "options:"
+    echo "    -h --help      show this help message"
+    echo "    -b --branch    change to the specified branch"
+    echo "    -f --fetch     fetch provided remote (or all if none specified)"
+    echo "    -r --remote    remote to be used"
+    echo "    -t --tag       change to the specified tag"
+}
+
+while [ -n "$1" ]; do
+    case $1 in
+        -h | --help)
+            help
+            exit 0
+            ;;
+        -b | --branch)
+            BRANCH="$2"
+            shift
+            ;;
+        -f | --fetch)
+            FETCH=1
+            ;;
+        -r | --remote)
+            REMOTE="$2"
+            shift
+            ;;
+        -t | --tag)
+            TAG="$2"
+            shift
+            ;;
+        *)
+            help
+            _die "unsupported argument \"$1\""
+            ;;
+    esac
+    shift
+done
+
+# check a branch or tag have been specified
+if [ -z "$BRANCH" ] && [ -z "$TAG" ]; then
+    _die "please specify a branch or a tag to switch to"
+fi
+if [ -n "$BRANCH" ] && [ -n "$TAG" ]; then
+    _die "please either specify a branch or a tag, not both"
+fi
+
+# optionally add the remote
+if [ -n "$REMOTE" ]; then
+    BRANCH="$REMOTE/$BRANCH"
+fi
+
+# change to the script directory (project root)
+pushd "$DIR" >/dev/null || exit 1
+
+# get list of submodules
+if ! [ -r .gitmodules ]; then
+    _die "project has no git submodules"
+fi
+SUBS=$(awk -F '"' '/submodule/ {print $2}' .gitmodules)
+
+# update submodule revs
+for sub in $SUBS; do
+    _head "---- submodule: $sub"
+    cd "$DIR/$sub" || exit 1
+    # make sure the remote exists, if specified
+    if [ -n "$REMOTE" ]; then
+        if ! git remote | grep -xq "$REMOTE"; then
+            _war "remote \"$REMOTE\" not found"
+            continue
+        fi
+    fi
+    # update repo
+    if [ "$FETCH" = 1 ]; then
+        if [ -n "$REMOTE" ]; then
+            git fetch "$REMOTE"
+        else
+            git fetch --all
+        fi
+    fi
+    # check if specified branch exists
+    if [ -n "$BRANCH" ]; then
+        if ! git branch -r | grep -wq "$BRANCH"; then
+            _war "branch \"$BRANCH\" not found"
+            continue
+        fi
+        # checkout the specified branch
+        git checkout "$BRANCH"
+        # pull latest changes
+        git pull
+    fi
+    if [ -n "$TAG" ]; then
+        if ! git tag | grep -xq "$TAG"; then
+            _war "tag \"$TAG\" not found"
+            continue
+        fi
+        # checkout the specified tag
+        git checkout "$TAG"
+    fi
+done
+
+# go back to calling directory
+popd >/dev/null || exit 1