Looping

Learn how to use loops in Taskfile to iterate over lists and execute commands multiple times.

Loop a static list / Loop the tasks

Assuming you have a Taskfile with a task to build the Docker images. You can use a loop to iterate over a static list of applications and build each one.

Taskfile.yml

version: '3'
tasks:
  image:build:
    vars:
      REPOSITORY: '{{.REPOSITORY}}'
      SRC: '{{.SRC}}'
    cmds:
      - docker build -t {{.REPOSITORY}}:latest {{.SRC}}
  build-all:
    cmds:
      - for:
          - app1
          - app2
        task: image:build
        vars:
          REPOSITORY: "{{.ITEM}}" # refer to app1, app2
          SRC: "{{.ITEM}}" # refer to app1, app2
  # run different atsks based on the loop value
  task-test:
    cmds:
      - echo "Running task test"
  task-build:
    cmds:
      - echo "Running task build"
  test-start:
    cmds:
      - for: [test, build]
        task: task-{{ .ITEM }} # refer to task-test, task-build

Demo and output

ubuntu@touted-mite:~$ task build-all 
task: [image:build] docker build -t app1:latest app1
[+] Building 5.9s (5/5) FINISHED                                docker:default
 => [internal] load build definition from Dockerfile                      0.0s
 => => transferring dockerfile: 56B                                       0.0s
 => [internal] load metadata for docker.io/library/ubuntu:latest          3.2s
 => [internal] load .dockerignore                                         0.0s
 => => transferring context: 2B                                           0.0s
 => [1/1] FROM docker.io/library/ubuntu:latest@sha256:6015f66923d7afbc53  2.5s
 => => resolve docker.io/library/ubuntu:latest@sha256:6015f66923d7afbc53  0.0s
 => => sha256:6015f66923d7afbc53558d7ccffd325d43b4e249f4 6.69kB / 6.69kB  0.0s
 => => sha256:dc17125eaac86538c57da886e494a34489122fb6a3ebb6 424B / 424B  0.0s
 => => sha256:a0e45e2ce6e6e22e73185397d162a64fcf2f80a41c 2.30kB / 2.30kB  0.0s
 => => sha256:0622fac788edde5d30e7bbd2688893e5452a19ff 29.72MB / 29.72MB  1.7s
 => => extracting sha256:0622fac788edde5d30e7bbd2688893e5452a19ff237a2e4  0.6s
 => exporting to image                                                    0.0s
 => => exporting layers                                                   0.0s
 => => writing image sha256:a3a57681676475ef2e0d451fcfd3daaca8d23d3ad42b  0.0s
 => => naming to docker.io/library/app1:latest                            0.0s
 
task: [image:build] docker build -t app2:latest app2
[+] Building 0.5s (5/5) FINISHED                                docker:default
 => [internal] load build definition from Dockerfile                      0.0s
 => => transferring dockerfile: 56B                                       0.0s
 => [internal] load metadata for docker.io/library/ubuntu:latest          0.3s
 => [internal] load .dockerignore                                         0.0s
 => => transferring context: 2B                                           0.0s
 => CACHED [1/1] FROM docker.io/library/ubuntu:latest@sha256:6015f66923d  0.0s
 => exporting to image                                                    0.0s
 => => exporting layers                                                   0.0s
 => => writing image sha256:a3a57681676475ef2e0d451fcfd3daaca8d23d3ad42b  0.0s
 => => naming to docker.io/library/app2:latest                            0.0s
ubuntu@touted-mite:~$ docker images
REPOSITORY    TAG       IMAGE ID       CREATED        SIZE
app1          latest    a3a576816764   4 weeks ago    78.1MB
app2          latest    a3a576816764   4 weeks ago    78.1MB

Loop a matrix

You can also loop over a matrix of values. This is useful when you have multiple variables that need to be combined in each iteration.

You can also reference the matrix to other variables as long as they are lists.

Taskfile.yml

version: '3'
tasks:
  image:build:
    vars:
      REPOSITORY: '{{.REPOSITORY}}'
      SRC: '{{.SRC}}'
      TAG: '{{.TAG}}'
    cmds:
      - docker build -t {{.REPOSITORY}}:{{.TAG}} {{.SRC}}
  build-all:
    cmds:
      - for:
          matrix:
            REPOSITORY: [app1, app2]
            TAG: [latest, v1.0]
        task: image:build
        vars:
          REPOSITORY: "{{.ITEM.REPOSITORY}}" # refer to app1, app2
          SRC: "{{.ITEM.REPOSITORY}}" # refer to app1, app2
          TAG: "{{.ITEM.TAG}}" # refer to latest, v1.0

This will generate the following images:

app1:latest
app1:v1.0
app2:latest
app2:v1.0

Demo and output

ubuntu@touted-mite:~$ docker images
REPOSITORY    TAG       IMAGE ID       CREATED        SIZE
app1          latest    a3a576816764   4 weeks ago    78.1MB
app1          v1.0      a3a576816764   4 weeks ago    78.1MB
app2          latest    a3a576816764   4 weeks ago    78.1MB
app2          v1.0      a3a576816764   4 weeks ago    78.1MB

Loop the task's `sources` or `generated` files

It is the same concept as above, but you can use the sources or generated files to loop over a list of files.

Taskfile.yml

version: '3'
tasks:
  default:
    sources:
      - foo.txt
      - bar.txt
    cmds:
      - for: sources
        cmd: cat {{ .ITEM }}

Loop the variables

If you want to loop over the variables, you can use the vars keyword. This is useful when you have a list of variables that need to be iterated over.

Taskfile.yml

version: '3'
tasks:
  loop1: # loop over a single variable
    vars:
      MY_VAR: hello world
    cmds:
      - for: { var: MY_VAR }
        cmd: echo {{ .ITEM }}
  loop2: # split and loop
    vars:
      MY_VAR: hello,world
    cmds:
      - for: { var: MY_VAR, split: ','}
        cmd: echo {{ .ITEM }}
  loop3: # loop over a list of variables
    vars:
      LIST: [hello, world]
    cmds:
      - for:
          var: LIST
        cmd: echo {{ .ITEM }}
  loop4: # loop over a map
    vars:
      MY_MAP:
        map:
          key1: hello
          key2: world
    cmds:
      - for:
          var: MY_MAP
        cmd: echo {{.KEY}} {{ .ITEM }} # KEY is the key, ITEM is the value
  loop5: # loop with dynamic variablses
    vars:
      MY_VAR:
        sh: find -type f -name '*.txt'
    cmds:
      - for: { var: MY_VAR }
        cmd: echo {{ .ITEM }}

Demo and output

ubuntu@touted-mite:~$ task loop1 loop2 loop3 loop4
task: [loop1] echo hello
hello
task: [loop1] echo world
world
task: [loop2] echo hello
hello
task: [loop2] echo world
world
task: [loop3] echo hello
hello
task: [loop3] echo world
world
task: [loop4] echo hello key1
hello key1
task: [loop4] echo world key2
world key2

Loop and rename variables

When you loop over a list of variables, you can also rename the variables using the as keyword.

Taskfile.yml

version: '3'
tasks:
  loop-rename:
    vars:
      LIST: [hello, world]
    cmds:
      - for:
          var: LIST
          as: MESSAGE
        cmd: echo {{ .MESSAGE }} # MESSAGE is the renamed variable

Loop the dependencies

Remember deps are run in parallel, so the iterations are not guaranteed to run in order.

Taskfile.yml

version: '3'
 
tasks:
  default:
    deps:
      - for: [foo, bar]
        task: my-task
        vars:
          FILE: '{{.ITEM}}'
 
  my-task:
    cmds:
      - echo '{{.FILE}}'

Loop a static list / Loop the tasks

Loop a matrix

Loop the task's sources or generated files

Loop the variables

Loop and rename variables

Loop the dependencies

On this page

Loop the task's `sources` or `generated` files