diff --git a/.github/workflows/lint.yml b/.github/workflows/lint.yml
new file mode 100644
index 0000000..759e41b
--- /dev/null
+++ b/.github/workflows/lint.yml
@@ -0,0 +1,16 @@
+name: Lint
+on:
+  push:
+    branches:
+      - master
+  pull_request:
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Lint
+        run: make lint
diff --git a/Dockerfile b/Dockerfile
index d78749e..e33e166 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -19,6 +19,7 @@ ENV S3_PATH 'backup'
 ENV S3_ENDPOINT **None**
 ENV S3_S3V4 no
 ENV SCHEDULE **None**
+ENV SUCCESS_WEBHOOK **None**
 
 ADD entrypoint.sh .
 ADD backup.sh .
diff --git a/Makefile b/Makefile
new file mode 100644
index 0000000..d0d204d
--- /dev/null
+++ b/Makefile
@@ -0,0 +1,4 @@
+SHELL_FILES := $(wildcard *.sh)
+
+lint:
+	@shellcheck --enable=require-variable-braces $(SHELL_FILES) && echo "ShellCheck passed"
diff --git a/README.md b/README.md
index b0ea5a0..57f7d1f 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@ This is a fork of [karser/postgres-backup-s3](https://github.com/karser/docker-i
 
 Docker:
 ```sh
-$ docker run -e S3_ACCESS_KEY_ID=key -e S3_SECRET_ACCESS_KEY=secret -e S3_BUCKET=my-bucket -e S3_PREFIX=backup -e POSTGRES_DATABASE=dbname -e POSTGRES_USER=user -e POSTGRES_PASSWORD=password -e POSTGRES_HOST=localhost f213/postgres-backup-s3
+$ docker run -e S3_ACCESS_KEY_ID=key -e S3_SECRET_ACCESS_KEY=secret -e S3_BUCKET=my-bucket -e S3_PREFIX=backup -e POSTGRES_DATABASE=dbname -e POSTGRES_USER=user -e POSTGRES_PASSWORD=password -e POSTGRES_HOST=localhost -e SCHEDULE="@daily" f213/postgres-backup-s3
 ```
 
 Docker Compose:
@@ -28,7 +28,7 @@ postgres-backup:
     test: curl http://localhost:1880
 
   environment:
-    SCHEDULE: 0 30 */2 * * *  # every 2 hours at HH:30
+    SCHEDULE: 0 30 */2 * * * *  # every 2 hours at HH:30
     S3_REGION: region
     S3_ACCESS_KEY_ID: key
     S3_SECRET_ACCESS_KEY: secret
@@ -42,8 +42,6 @@ postgres-backup:
     SUCCESS_WEBHOOK: https://sb-ping.ru/8pp9RGwDDPzTL2R8MRb8Ae
 ```
 
-### Automatic Periodic Backups
+### Crontab format
 
-You can additionally set the `SCHEDULE` environment variable like `-e SCHEDULE="@daily"` to run the backup automatically.
-
-More information about the scheduling can be found [here](http://godoc.org/github.com/robfig/cron#hdr-Predefined_schedules).
+Schedule format with years support. More information about the scheduling can be found [here](https://github.com/aptible/supercronic/tree/master?tab=readme-ov-file#crontab-format)
diff --git a/backup.sh b/backup.sh
index 4928409..6b05931 100644
--- a/backup.sh
+++ b/backup.sh
@@ -1,5 +1,8 @@
 #! /bin/sh
 
+# shellcheck disable=SC3040  # expecting 'pipefail' derrictive is availabe in the shell
+# shellcheck disable=SC2086  # POSTGRES_HOST_OPTS and AWS_ARGS should be splitted by spaces intentionally
+
 set -e
 set -o pipefail
 
@@ -25,8 +28,8 @@ fi
 
 if [ "${POSTGRES_HOST}" = "**None**" ]; then
   if [ -n "${POSTGRES_PORT_5432_TCP_ADDR}" ]; then
-    POSTGRES_HOST=$POSTGRES_PORT_5432_TCP_ADDR
-    POSTGRES_PORT=$POSTGRES_PORT_5432_TCP_PORT
+    POSTGRES_HOST="${POSTGRES_PORT_5432_TCP_ADDR}"
+    POSTGRES_PORT="${POSTGRES_PORT_5432_TCP_PORT}"
   else
     echo "You need to set the POSTGRES_HOST environment variable."
     exit 1
@@ -43,33 +46,33 @@ if [ "${POSTGRES_PASSWORD}" = "**None**" ]; then
   exit 1
 fi
 
-if [ "${S3_ENDPOINT}" == "**None**" ]; then
+if [ "${S3_ENDPOINT}" = "**None**" ]; then
   AWS_ARGS=""
 else
   AWS_ARGS="--endpoint-url ${S3_ENDPOINT}"
 fi
 
 # env vars needed for aws tools
-export AWS_ACCESS_KEY_ID=$S3_ACCESS_KEY_ID
-export AWS_SECRET_ACCESS_KEY=$S3_SECRET_ACCESS_KEY
-export AWS_DEFAULT_REGION=$S3_REGION
+export AWS_ACCESS_KEY_ID="${S3_ACCESS_KEY_ID}"
+export AWS_SECRET_ACCESS_KEY="${S3_SECRET_ACCESS_KEY}"
+export AWS_DEFAULT_REGION="${S3_REGION}"
 
-export PGPASSWORD=$POSTGRES_PASSWORD
-POSTGRES_HOST_OPTS="-h $POSTGRES_HOST -p $POSTGRES_PORT -U $POSTGRES_USER $POSTGRES_EXTRA_OPTS"
+export PGPASSWORD="${POSTGRES_PASSWORD}"
+POSTGRES_HOST_OPTS="-h ${POSTGRES_HOST} -p ${POSTGRES_PORT} -U ${POSTGRES_USER} ${POSTGRES_EXTRA_OPTS}"
 
 echo "Creating dump of ${POSTGRES_DATABASE} database from ${POSTGRES_HOST}..."
 
-pg_dump -Fc $POSTGRES_HOST_OPTS $POSTGRES_DATABASE > db.dump
+pg_dump -Fc ${POSTGRES_HOST_OPTS} "${POSTGRES_DATABASE}" > db.dump
 
-echo "Uploading dump to $S3_BUCKET"
+echo "Uploading dump to ${S3_BUCKET}"
 
-cat db.dump | aws $AWS_ARGS s3 cp - s3://$S3_BUCKET/$S3_PREFIX/${POSTGRES_DATABASE}_$(date +"%Y-%m-%dT%H:%M:%SZ").dump || exit 2
+aws ${AWS_ARGS} s3 cp db.dump "s3://${S3_BUCKET}/${S3_PREFIX}/${POSTGRES_DATABASE}_$(date +"%Y-%m-%dT%H:%M:%SZ").dump" || exit 2
 
 echo "DB backup uploaded successfully"
 
 rm db.dump
 
-if [ -n $SUCCESS_WEBHOOK ]; then
-    echo "Notifying $SUCCESS_WEBHOOK"
-    curl -m 10 --retry 5 $SUCCESS_WEBHOOK
+if [ ! "${SUCCESS_WEBHOOK}" = "**None**" ]; then
+    echo "Notifying ${SUCCESS_WEBHOOK}"
+    curl -m 10 --retry 5 "${SUCCESS_WEBHOOK}"
 fi