diff --git a/opam-release.sh b/opam-release.sh
index 8e780cc..117d4b0 100755
--- a/opam-release.sh
+++ b/opam-release.sh
@@ -1,5 +1,6 @@
 #!/usr/bin/env bash
 set -e
+shopt -s nullglob
 
 if [ "$DEBUG" = 1 ]; then
   set -x
@@ -7,23 +8,23 @@ fi
 
 show_help(){
     cat <<EOF
-Usage : opam-release (arguments)* (opam-files)*
+Usage : opam-release (options)* (opam-files)*
 --
-Optional arguments:
-  opam-files: one or many opam files to push to opam-coq-archive
-    *if no argument is provided, it lists *.opam files in the current directory
-  -u GITHUBUSER / --user GITHUBUSER:
-    where GITHUBUSER is your github username,
+opam-files: an opam file to push to opam-coq-archive
+  * if no argument is provided, it lists *.opam files in the current directory
+options:
+  -u GITHUB_USER / --user GITHUB_USER:
+    where GITHUB_USER is your github username,
     you must have a fork of coq/opam-coq-archive under
-    https://github.com/$GITHUBUSER/opam-coq-archive
+    https://github.com/$GITHUB_USER/opam-coq-archive
     for this command to work,
     * if not provided, tries "git config --get github.user"
+      which you can set using "git config --global github.user GITHUB_SER"
   -p PROJECT / --project PROJECT:
-    where PROJECT is a name of the project,
-    without space, it is used solely for generating
-    the name of the branch and PR,
-    * automatically infered from the name of the opam file
-    if only one was given,
+    where PROJECT is a name of the project, without space,
+    it is used solely for generating  the name of the branch and PR,
+    * automatically infered from the name of the opam file,
+      if only one was given.
   -e DEPTH / --depth DEPTH:
     sets the depth of the local clone of opam-coq-archive to $DEPTH
     * defaults to full clone,
@@ -38,16 +39,25 @@ Optional arguments:
     with the version to release.
     * tries to infer it from the "dev-repo" section if one opam file is provided
   -x PREFIX / --version-prefix PREFIX: the tag of a version is equal to $PREFIX$VERSION
-     * default is ""
+     *  default is ""
      ** this options is used only if URL is not provided
+  -r / --local-opam-coq-archive LOCAL_OCA: where LOCAL8OCA is the path to
+     a local copy of the opam-coq-archive repository
   -d / --dev: pushes an update to extra-dev instead of releases
   -C / --no-check-upstream: tells opam lint not to check the sum online
+  -c / --check-upstream: foce opam lint to check the sum online, (even
+    if it was disable for some reason, e.g. incompatible opam version)
   -h / -? / --help: print this usage
   -s / --show-defaults: prints the default inferred setting and exists
   -v / --verbose: show debug information
   -L / --no-lint: do not run opam lint
     (not recommended but useful if you do not have opam installed)
+  -l / --lint: force opam lint, (even if it was disabled for some reason)
   -n / --do-nothing: do not push anything
+--
+All above options can be set with the corresponding environment variable.
+Additionally, one may use the DEBUG environement variable tuo turn on
+debugging through options -x.
 EOF
 }
 
@@ -56,20 +66,37 @@ die() {
     exit 1
 }
 
-GITHUBUSER=$(git config --get github.user)
-TAG=$(git describe --tags --abbrev=0)
-VERSION=$(echo $TAG | sed -e "s/[^0-9]*\(\([0-9]+|\.\)\)*/\1/")
-PROJECT=
-URL=
-LINT=1
-NOTHING=0
-DEPTH=
-HDEPTH=
-TARGET="released"
+# Checking git and opam are installed
+if ! command -v git &> /dev/null; then
+    die "ERROR: git cannot be found, you must install it."
+fi
+if ! command -v opam &> /dev/null; then
+    die "ERROR: opam cannot be found, you must install it."
+fi
+# checking opam version
+verle() {
+    [ "$1" = "`echo -e "$1\n$2" | sort -V | head -n1`" ]
+}
+if verle "2.1.0" $(opam --version); then
+  CHECKUPSTREAM="${CHECKUPSTREAM:---check-upstream}"
+fi
+#
+
+# trying to retrieve github user
+GITHUB_USER="${GITHUB_USER:-$(git config --default '' --get github.user)}"
+
+if ! [ "$TAG" ]; then
+    if (git describe --tags &> /dev/null) then
+       TAG=$(git describe --tags --abbrev=0)
+    fi
+fi
+VERSION="${VERSION:-$(echo $TAG | sed -e 's/[^0-9]*\(\([0-9]+|\.\)\)*/\1/')}"
+PROJECT="${PROJECT:-}"
+LINT="${LINT:-1}"
+NOTHING="${NOTHING:-0}"
+TARGET="${TARGET:-released}"
+SHOWDEFAULTS="${SHOWDEFAULTS:-0}"
 OPAM=()
-CHECKUPSTREAM="--check-upstream"
-PREFIX=
-SHOWDEFAULTS=0
 
 while :; do
     case $1 in
@@ -78,35 +105,43 @@ while :; do
             exit 0
             ;;
         -u|--user)
-            if [ "$2" ]; then GITHUBUSER=$2; shift; shift
+            if [ "$2" ]; then GITHUB_USER=$2; shift; shift
             else die 'ERROR: "--user" requires a non-empty argument, cf --help'
             fi
             ;;
         -p|--project)
             if [ "$2" ]; then PROJECT=$2; shift; shift
-            else die 'ERROR: "--name" requires a non-empty argument, cf --help'
+            else die 'ERROR: "--project" requires a non-empty argument, cf --help'
             fi
             ;;
         -V|--version)
             if [ "$2" ]; then VERSION=$2; shift; shift
-            else die 'ERROR: "--name" requires a non-empty argument, cf --help'
+            else die 'ERROR: "--version" requires a non-empty argument, cf --help'
             fi
             ;;
         -U|--url)
             if [ "$2" ]; then URL=$2; shift; shift
-            else die 'ERROR: "--name" requires a non-empty argument, cf --help'
+            else die 'ERROR: "--url" requires a non-empty argument, cf --help'
             fi
             ;;
         -e|--depth)
             if [ "$2" ]; then HDEPTH="$2"; DEPTH="--depth=$2"; shift; shift
-            else die 'ERROR: "--name" requires a non-empty argument, cf --help'
+            else die 'ERROR: "--depth" requires a non-empty argument, cf --help'
             fi
             ;;
         -x|--version-prefix)
             if [ "$2" ]; then PREFIX=$2; shift; shift
-            else die 'ERROR: "--name" requires a non-empty argument, cf --help'
+            else die 'ERROR: "--version-prefix" requires a non-empty argument, cf --help'
             fi
             ;;
+        -r|--local-opam-coq-archive)
+            if [ "$2" ]; then LOCAL_OCA=$2; shift; shift
+            else die 'ERROR: "--local-opam-coq-archive" requires a non-empty argument, cf --help'
+            fi
+            ;;
+        -l|--lint)
+            LINT=1; shift
+            ;;
         -L|--no-lint)
             LINT=0; shift
             ;;
@@ -116,6 +151,10 @@ while :; do
             CHECKUPSTREAM=
             shift
             ;;
+        -c|--check-upstream)
+            CHECKUPSTREAM="--check-upstream"
+            shift
+            ;;
         -C|--no-check-upstream)
             CHECKUPSTREAM=
             shift
@@ -133,9 +172,9 @@ while :; do
             if ! [ "$*" ]; then
                 break
             elif [ -f "$1" ]; then
-               OPAM+=("$1")
-               shift
-            else die 'ERROR: positional arguments must be a file'
+                OPAM+=("$1")
+                shift
+            else die 'ERROR: positional argument must be an existing file.'
             fi
             ;;
     esac
@@ -147,15 +186,14 @@ fi
 
 eval set -- "${OPAM[@]}"
 
-if ! [ "GITHUBUSER" ]; then
-     die 'ERROR: -u / --user argument is required, cf --help'
+if ! [ "$GITHUB_USER" ]; then
+    die 'ERROR: -u / --user argument is required, cf --help'
 fi
 
-if ! [ "VERSION" ]; then
+if ! [ "$VERSION" ]; then
     die 'ERROR: -V / --version argument is required, cf --help'
 fi
 
-
 if [ "$PREFIX" ]; then
     TAG=$PREFIX$VERSION
 fi
@@ -171,7 +209,7 @@ case "${#OPAM[@]}" in
         ;;
     *)
         if ! [ "$PROJECT" ]; then
-            die 'ERROR: -p / --project argument is required when more than one opam files are given, cf --help'
+            die 'ERROR: --project argument is required when more than one opam files are given, cf --help'
         fi
         ;;
 esac
@@ -184,14 +222,40 @@ if ! [ "$URL" ]; then
     fi
 fi
 
-if [ "$VERBOSE" = 1 ] || [ "$SHOWDEFAULTS" = 1 ]; then
+if ! [ "$URL" ]; then
+    die 'ERROR: --url argument cannot be inferred, please provide it manually, cf --help'
+fi
+
+if [ "$VERBOSE" = 1 ]; then
+    echo "DEBUG=$DEBUG";
+    echo "TAG=$TAG";
+    echo "PREFIX=$PREFIX";
+    echo "VERSION=$VERSION";
+    echo "VERBOSE=$VERBOSE";
+    echo "PROJECT=$PROJECT";
+    echo "GITHUB_USER=$GITHUB_USER";
+    echo "URL=$URL";
+    echo "LINT=$LINT";
+    echo "NOTHING=$NOTHING";
+    echo "DEPTH=$DEPTH";
+    echo "HDEPTH=$HDEPTH";
+    echo "TARGET=$TARGET";
+    echo "OPAM=$OPAM";
+    echo "CHECKUPSTREAM=$CHECKUPSTREAM";
+    echo "PREFIX=$PREFIX";
+    echo "SHOWDEFAULTS=$SHOWDEFAULTS";
+    echo "LOCAL_OCA=$LOCAL_OCA";
+fi
+
+if [ "$SHOWDEFAULTS" = 1 ]; then
     echo "# this would call"
     echo "$0 \\"
     if [ "$VERBOSE" = 1 ]; then echo "-v \\"; fi
-    echo "-u $GITHUBUSER \\"
+    echo "-u $GITHUB_USER \\"
     echo "-V $VERSION \\"
     echo "-p $PROJECT \\"
     echo "-U $URL \\"
+    if [ "$LOCAL_OCA" ]; then echo "-r $LOCAL_OCA \\"; fi
     if [ "$LINT" = 0 ]; then echo "-L \\"; fi
     if [ "$NOTHING" = 1 ]; then echo "-n \\"; fi
     if [ "$HDEPTH" ]; then echo "-e $HDEPTH \\"; fi
@@ -204,12 +268,19 @@ if [ "$SHOWDEFAULTS" = 1 ]; then
     exit
 fi
 
-COA=$(mktemp -d) # stands for Coq Opam Archive
-git clone $DEPTH git@github.com:coq/opam-coq-archive $COA -o upstream
-git -C $COA remote add origin git@github.com:$GITHUBUSER/opam-coq-archive
+TMP_OCA=$(mktemp -d) # stands for Opam Coq Archive
+if [ "$LOCAL_OCA" ]; then
+  git clone $LOCAL_OCA $TMP_OCA -o local
+  git -C $TMP_OCA remote add upstream git@github.com:coq/opam-coq-archive
+  git -C $TMP_OCA fetch upstream master
+  git -C $TMP_OCA reset --hard upstream/master
+else
+  git clone $DEPTH git@github.com:coq/opam-coq-archive $TMP_OCA -o upstream
+fi
+git -C $TMP_OCA remote add origin git@github.com:$GITHUB_USER/opam-coq-archive
 BRANCH=$PROJECT.$VERSION
-git -C $COA checkout -b $BRANCH
-PKGS=$COA/$TARGET/packages
+git -C $TMP_OCA checkout -b $BRANCH
+PKGS=$TMP_OCA/$TARGET/packages
 
 ARCHIVE=$(mktemp)
 if [ "$TARGET" = "released" ]; then
@@ -218,7 +289,7 @@ if [ "$TARGET" = "released" ]; then
 fi
 
 if [ "$VERBOSE" = 1 ]; then
-    echo "COA=$COA"
+    echo "TMP_OCA=$TMP_OCA"
     echo "BRANCH=$BRANCH"
     echo "PKGS=$PKGS"
     echo "ARCHIVE=$ARCHIVE"
@@ -243,24 +314,24 @@ for opam in ${OPAM[@]}; do
     else
         echo "linting disabled (not recommended)"
     fi
-    git -C $COA add $P/opam
+    git -C $TMP_OCA add $P/opam
 done
 
-git -C $COA commit -m "Update $PROJECT $VERSION"
+git -C $TMP_OCA commit -m "Update $PROJECT $VERSION"
 if [ "$NOTHING" = 1 ]; then
     echo "**********************************************************************"
     echo "Dry run!"
-    echo git -C $COA push origin -f $BRANCH
+    echo git -C $TMP_OCA push origin -f $BRANCH
     echo "if you want to see the diff, run"
-    echo git -C $COA diff HEAD~1
+    echo git -C $TMP_OCA diff HEAD~1
     echo "**********************************************************************"
 else
-    git -C $COA push origin -f $BRANCH
+    git -C $TMP_OCA push origin -f $BRANCH
     echo "**********************************************************************"
     echo "Create a pull request by visiting"
-    echo "https://github.com/$GITHUBUSER/opam-coq-archive/pull/new/$BRANCH"
+    echo "https://github.com/$GITHUB_USER/opam-coq-archive/pull/new/$BRANCH"
     echo "**** PLEASE CHECK CAREFULLY THE GENERATED CODE ***"
     echo "If you wish to delete the resulting branch, execute:"
-    echo "git -C $COA push origin --delete $BRANCH"
+    echo "git -C $TMP_OCA push origin --delete $BRANCH"
     echo "**********************************************************************"
 fi