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Automatic build tool for all your projects
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Snag Build Status Coverage Status

An automatic build tool for all your needs



You can visit the releases section to download the binary for your platform.


We've got a formula in homebrew!

brew update && brew install snag


If you have go installed and want to install the latest and greatest you can run:

$ go get


Once snag is installed, use:

snag init

This will generate the snag file .snag.yml. Here is a sample of the snag file:

verbose: true
  - .git
  - "**.ext"
  - "foo/**/"
  - echo "lint code"
  - echo "test code"

Snag works by reading the snag file allowing you to configure what and how commands will be executed. The file must reside in the same directory that you want to watch.

By default, snag will watch all files/folders within the current directory recursively. The ignore section will tell snag to ignore any changes that happen to the directories/files listed. The ignore section uses the same pattern matching that gitignore uses.

The build section of the file will be executed when any file is created, deleted, or modified.

Once configured, use:


From a project with a snag file and develop away!

Quick Use

If you find yourself working on a project that does not contain a snag file and still want to use snag, you can use flags to specify commands to run.

The -c flag allows specifying a command just like the snag file and can be defined more than once for multiple commands. The order of the commands depends on the order of the flag.

snag -c "echo snag world" -c "echo rocks"

will output

|Passed     | echo snag world
|Passed     | echo rocks

The -v flag enables verbose output. It will also override the verbose option form the snag file if it is defined to false.

NOTE: using the -c flag will skip reading a snag file even if it exists in the current working directory.

Environment Variables

You can access your shell's environment variables by using $$.

  - echo $$MY_VAR
  - rm -rf $$OUTPUT_DIR


Endless build loops

Snag will run your configured commands when ANY file, not ignored, is modifed in your current directory. If your commands generate any files within the watched directory, you must add them to the ignore section in your snag file to avoid an endless build loop.

Trouble running shell scripts

In order to run shell scripts, your must have a shebang in it. If you are trying to run a script without a shebang, you will need to specify the shell it should run in.


Running a script with a shebang

  - ./my-script

Running a script without a shebang

  - bash my-script

Ignore Pattern Matching

If you want to use asterisks in the ignore section of your snag file, you need to make sure to wrap them in quotes or you may run into an error like:

$ snag
2015/10/24 19:39:40 Could not parse yml file. yaml: line 6: did not find expected alphabetic or numeric character

Known Issues

  • open /dev/null: too many open files

You may experience this error if you're running on OSX. You may need to bump the maximum number of open file on your machine. You can refer to this article for more information on the max files on OSX and this superuser post for a solution

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