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# Task - Simple task runner / "Make" alternative

Task is a simple tool that allows you to easily run development and build
tasks. Task is written in Golang, but can be used to develop any language.
It aims to be simpler and easier to use then [GNU Make][make].

- [Installation](#installation)
- [Usage](#usage)
  - [Environment](#environment)
  - [OS specific task](#os-specific-task)
  - [Task directory](#task-directory)
  - [Task dependencies](#task-dependencies)
  - [Calling another task](#calling-another-task)
  - [Prevent unnecessary work](#prevent-unnecessary-work)
  - [Variables](#variables)
    - [Dynamic variables](#dynamic-variables)
  - [Go's template engine](#gos-template-engine)
  - [Help](#help)
  - [Watch tasks](#watch-tasks-experimental)
- [Alternative task runners](#alternative-task-runners)

## Installation

If you have a [Golang][golang] environment setup, you can simply run:

```bash
go get -u -v github.com/go-task/task/cmd/task
```

Or you can download the binary from the [releases][releases] page and add to
your `PATH`. DEB and RPM packages are also available.
The `task_checksums.txt` file contains the SHA-256 checksum for each file.

## Usage

Create a file called `Taskfile.yml` in the root of the project.
The `cmds` attribute should contains the commands of a task:

```yml
build:
  cmds:
    - go build -v -i main.go

assets:
  cmds:
    - gulp
```

Running the tasks is as simple as running:

```bash
task assets build
```

Task uses [github.com/mvdan/sh](https://github.com/mvdan/sh), a native Go sh
interpreter. So you can write sh/bash commands and it will work even on
Windows, where `sh` or `bash` is usually not available. Just remember any
executable called must be available by the OS or in PATH.

If you ommit a task name, "default" will be assumed.

### Environment

You can specify environment variables that are added when running a command:

```yml
build:
  cmds:
    - echo $hallo
  env:
    hallo: welt
```

### OS specific task

If you add a `Taskfile_{{GOOS}}.yml` you can override or amend your taskfile
based on the operating system.

Example:

Taskfile.yml:

```yml
build:
  cmds:
    - echo "default"
```

Taskfile_linux.yml:

```yml
build:
  cmds:
    - echo "linux"
```

Will print out `linux` and not default.

It's also possible to have OS specific `Taskvars.yml` file, like
`Taskvars_windows.yml` or `Taskvars_darwin.yml`. See the
[variables section](#variables) below.

### Task directory

By default, tasks will be executed in the directory where the Taskfile is
located. But you can easily make the task run in another folder informing
`dir`:

```yml
js:
  dir: www/public/js
  cmds:
    - gulp
```

### Task dependencies

You may have tasks that depends on others. Just pointing them on `deps` will
make them run automatically before running the parent task:

```yml
build:
  deps: [assets]
  cmds:
    - go build -v -i main.go

assets:
  cmds:
    - gulp
```

In the above example, `assets` will always run right before `build` if you run
`task build`.

A task can have only dependencies and no commands to group tasks together:

```yml
assets:
  deps: [js, css]

js:
  cmds:
    - npm run buildjs

css:
  cmds:
    - npm run buildcss
```

If there are more than one dependency, they always run in parallel for better
performance.

Each task can only be run once. If it is included from another dependend task causing
a cyclomatic dependency, execution will be stopped.

```yml
task1:
  deps: [task2]

task2:
  deps: [task1]
```

The above will fail with the message: "cyclic dependency detected".

### Calling another task

When a task has many dependencies, they are executed concurrently. This will
often result in a faster build pipeline. But in some situations you may need
to call other tasks serially. In this case, just use the following syntax:

```yml
main-task:
  cmds:
    - task: task-to-be-called
    - task: another-task
    - echo "Both done"

task-to-be-called:
  cmds:
    - echo "Task to be called"

another-task:
  cmds:
    - echo "Another task"
```

Overriding variables in the called task is as simple as informing `vars`
attribute:

```yml
main-task:
  cmds:
    - task: write-file
      vars: {FILE: "hello.txt", CONTENT: "Hello!"}
    - task: write-file
      vars: {FILE: "world.txt", CONTENT: "World!"}

write-file:
  cmds:
    - echo "{{.CONTENT}}" > {{.FILE}}
```

The above syntax is also supported in `deps`.

> NOTE: It's also possible to call a task without any param prefixing it
with `^`, but this syntax is deprecaded:

```yml
a-task:
  cmds:
    - ^another-task

another-task:
  cmds:
    - echo "Another task"
```

### Prevent unnecessary work

If a task generates something, you can inform Task the source and generated
files, so Task will prevent to run them if not necessary.

```yml
build:
  deps: [js, css]
  cmds:
    - go build -v -i main.go

js:
  cmds:
    - npm run buildjs
  sources:
    - js/src/**/*.js
  generates:
    - public/bundle.js

css:
  cmds:
    - npm run buildcss
  sources:
    - css/src/*.css
  generates:
    - public/bundle.css
```

`sources` and `generates` should be file patterns. When both are given, Task
will compare the modification date/time of the files to determine if it's
necessary to run the task. If not, it will just print
`Task "js" is up to date`.

Alternatively, you can inform a sequence of tests as `status`. If no error
is returned (exit status 0), the task is considered up-to-date:

```yml
generate-files:
  cmds:
    - mkdir directory
    - touch directory/file1.txt
    - touch directory/file2.txt
  # test existence of files
  status:
    - test -d directory
    - test -f directory/file1.txt
    - test -f directory/file2.txt
```

You can use `--force` or `-f` if you want to force a task to run even when
up-to-date.

### Variables

When doing interpolation of variables, Task will look for the below.
They are listed below in order of importance (e.g. most important first):

- Variables given while calling a task from another.
  (See [Calling another task](#calling-another-task) above)
- Environment variables
- Variables declared locally in the task
- Variables available in the `Taskvars.yml` file

Example of overriding with environment variables:

```bash
$ TASK_VARIABLE=a-value task do-something
```

Example of locally declared vars:

```yml
print-var:
  cmds:
    echo "{{.VAR}}"
  vars:
    VAR: Hello!
```

Example of `Taskvars.yml` file:

```yml
PROJECT_NAME: My Project
DEV_MODE: production
GIT_COMMIT: {sh: git log -n 1 --format=%h}
```

> NOTE: It's also possible setting a variable globally using `set` attribute
in task, but this is deprecated:

```yml
build:
  deps: [set-message]
  cmds:
    - echo "Message: {{.MESSAGE}}"

set-message:
  cmds:
    - echo "This is an important message"
  set: MESSAGE
```

#### Dynamic variables

The below syntax (`sh:` prop in a variable) is considered a dynamic
variable. The value will be treated as a command and the output assigned.

```yml
build:
  cmds:
    - go build -ldflags="-X main.Version={{.GIT_COMMIT}}" main.go
  vars:
    GIT_COMMIT:
      sh: git log -n 1 --format=%h
```

This works for all types of variables.

> It's also possible to prefix the variable with `$` to have a dynamic
variable, but this is now considered deprecated:

```yml
# Taskvars.yml

# recommended
GIT_COMMIT:
  sh: git log -n 1 --format=%h

# deprecated
GIT_COMMIT: $git log -n 1 --format=%h
```

### Go's template engine

Task parse commands as [Go's template engine][gotemplate] before executing
them. Variables are acessible through dot syntax (`.VARNAME`).

All functions by the Go's [sprig lib](http://masterminds.github.io/sprig/)
are available. The following example gets the current date in a given format:

```yml
print-date:
  cmds:
    - echo {{now | date "2006-01-02"}}
```

Task also adds the following functions:

- `OS`: Returns operating system. Possible values are "windows", "linux",
  "darwin" (macOS) and "freebsd".
- `ARCH`: return the architecture Task was compiled to: "386", "amd64", "arm"
  or "s390x".
- `ToSlash`: Does nothing on Unix, but on Windows converts a string from `\`
  path format to `/`.
- `FromSlash`: Oposite of `ToSlash`. Does nothing on Unix, but on Windows
  converts a string from `\` path format to `/`.
- `ExeExt`: Returns the right executable extension for the current OS
  (`".exe"` for Windows, `""` for others).

Example:

```yml
print-os:
  cmds:
    - echo '{{OS}} {{ARCH}}'
    - echo '{{if eq OS "windows"}}windows-command{{else}}unix-command{{end}}'
    # This will be path/to/file on Unix but path\to\file on Windows
    - echo '{{FromSlash "path/to/file"}}'
```

### Help

Running `task --list` (or `task -l`) lists all tasks with a description.
The following taskfile:

```yml
build:
  desc: Build the go binary.
  cmds:
    - go build -v -i main.go

test:
  desc: Run all the go tests.
  cmds:
    - go test -race ./...

js:
  cmds:
    - npm run buildjs

css:
  cmds:
    - npm run buildcss
```

would print the following output:

```bash
* build:   Build the go binary.
* test:    Run all the go tests.
```

## Watch tasks (experimental)

If you give a `--watch` or `-w` argument, task will watch for files changes
and run the task again. This requires the `sources` attribute to be given,
so task know which files to watch.

## Alternative task runners

- YAML based:
  - [tj/robo][robo]
  - [dogtools/dog][dog]
  - [goeuro/myke][myke]
- Go based:
  - [go-godo][godo]
  - [markbates/grift][grift]

[make]: https://www.gnu.org/software/make/
[releases]: https://github.com/go-task/task/releases
[golang]: https://golang.org/
[gotemplate]: https://golang.org/pkg/text/template/
[robo]: https://github.com/tj/robo
[dog]: https://github.com/dogtools/dog
[myke]: https://github.com/goeuro/myke
[godo]: https://github.com/go-godo/godo
[grift]: https://github.com/markbates/grift
[sh]: https://github.com/mvdan/sh
