A database migration tool written in BASH consisting of just one file -
$ cd shmig $ make install $ cd $HOME $ mkdir migrations $ shmig -t sqlite3 -d test.db create mytable generated ./migrations/1470490964-mytable.sql $ cat ./migrations/1470490964-mytable.sql -- Migration: mytable -- Created at: 2016-08-06 09:42:44 -- ==== UP ==== BEGIN; PRAGMA foreign_keys = ON; COMMIT; -- ==== DOWN ==== BEGIN; COMMIT; $ # In normal usage, you would add SQL to this migration file. $ shmig -t sqlite3 -d test.db migrate shmig: creating migrations table: shmig_version shmig: applying 'mytable' (1470490964)... done $ ls -l test.db -rw-r--r-- 1 mark staff 12288 Aug 6 09:41 test.db $ shmig -t sqlite3 -d test.db rollback shmig: reverting 'mytable' (1470490964)... done $ shmig -h | wc -l 73 $
See test/sql for a few more examples.
Currently there are lots of database migration tools such as DBV, Liquibase, sqitch, Flyway and other framework-specific ones (for Ruby on Rails, Yii, Laravel, ...). But they all are pretty heavy, with lots of dependencies (or even unusable outside of their stack), some own DSLs...
I needed some simple, reliable solution with minimum dependencies and able to run in pretty much any POSIX-compatible environment against different databases (PostgreSQL, MySQL, SQLite3).
And here's the result.
RDMS'es are bundled along with their console clients. MySQL has
mysql, PostgreSQL has
psql and SQLite3 has
sqlite3. And that's it! This is enough for interacting with database in batch mode w/o any drivers or connectors.
Using client options one can make its output suitable for batch processing with standard UNIX text-processing tools (
awk, ...). This is enough for implementing simple migration system that will store current schema version information withing database (see
SCHEMA_TABLE variable in
SHMIG tries to read configuration from the configuration file
shmig.conf in the current working directory. A sample configuration
You can also provide an optional config override file by creating the file
This allows you to provide a default configuration which is version-controlled with your project,
then specify a non-version-controlled local config file that you can use to provide
instance-specific config. (An alternative is to use envrionment variables, though some people
prefer concrete files to nebulous environment variables.) This works even with custom config
files specified with the
You can also configure SHMIG from command line, or by using environmental variables. The command line settings have higher priority than configuration files or environment settings.
Required options are:
-t- database type
-d- database to operate on
-m- directory with migrations
All other options (see
shmig -h) are not necessary.
To simplify usage you should create
shmig.conf file in your project root directory and put there configuration then just run
shmig <action> ... in that directory.
For detailed information see
Migrations are SQL files whose name starts with "
and end with ".sql". The order that new migrations are applied is
by the seconds-since-epoch time stamp in the filename, with the
oldest migration going first.
Each migration contains two special markers:
-- ==== UP ==== that marks start of section that will be executed when migration is applied and
-- ==== DOWN ==== that marks start of section that will be executed when migration is reverted.
-- Migration: create users table -- Created at: 2013-10-02 07:03:11 -- ==== UP ==== CREATE TABLE `users`( id int not null primary key auto_increment, name varchar(32) not null, email varchar(255) not null ); CREATE UNIQUE INDEX `users_email_uq` ON `users`(`email`); -- ==== DOWN ==== DROP TABLE `users`;
-- ==== UP ==== till
-- ==== DOWN ==== will be executed when migration is applied and everything between
-- ==== DOWN ==== till the end of file will be executed when migration is reverted. If migration is missing marker or contents of marker is empty then appropriate action will fail (i.e. if you're trying to revert migration that has no or empty
-- ==== DOWN ==== marker you'll get an error and script won't execute any migrations following script with error). Also note those semicolons terminating statements. They're required because you're basically typing that into your database CLI client.
SHMIG can generate skeleton migration for you, see
Migrations with test data
One nice feature of Liquibase is contexts, which are used to implement different behavior based on environment; for example, in a development environment you can insert test data.
shmig can support this with symbolic links. For example, say
your production migrations are in
prod and test data in
. └── migrations ├── prod │ └── 1485643154-create_table.sql └── test └── 1485648520-testdata.sql
To create a test environment context, link the prod SQL in test directory:
$ cd migrations/test/ $ ln -s ../prod/1485643154-create_table.sql
. └── migrations ├── prod │ └── 1485643154-create_table.sql └── test ├── 1485643154-create_table.sql -> ../prod/1485643154-create_table.sql └── 1485648520-testdata.sql
When applying migrations to test, point shmig to the test directory either via the command line or using the local config override file.
Since migrations are applied in order of epoch seconds in the file name, this works.
This is very early release. I've tried it with SQLite3, PostgreSQL, MySQL databases and didn't find any bugs. If you find any then please report them along with your migrations (or similar that will allow to reproduce bug), tools versions, detailed description of steps and configuration file (w/o DB credentials).
Password is passed to
psql via environment variable. This can be a security issue if your system allows other users to read environment of process that belongs to another user. In most Linux distributions with modern kernels this is forbidden. You can check this (on systems supporting /proc file system) like this:
cat /proc/1/env - if you get permission denied error then you're secure.
Because SHMIG is just a shell script it's not a speed champion. Every time a statement is executed new client process is spawned. I didn't experience much issues with speed, but if you'll have then please file an issue and maybe I'll get to that in detail.
Usage with Docker
Shmig can be used and configured with env vars
docker run -e PASSWORD=root -e HOST=mariadb -v $(pwd)/migrations:/sql --link mariadb:mariadb mkbucc/shmig:latest -t mysql -d db-name up
- Speed. Some optimizations are definitely possible to speed things up.
- A way to spawn just one CLI client. Maybe something with FIFOs and SIGCHLD handler.
- Better documentation :\