Running bash scripts

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This page explains how to configure Cloud Build to run bash scripts within a build step. If you're new to Cloud Build, read the quickstarts and the Build configuration overview first.

You can run bash scripts within a build step to configure a number of workflows including:

  • Running multiple commands in one build step.
  • Reading from the filesystem.
  • Building in logic such as retries or conditionals.
  • Outputting to the log, for example, running echo $VARNAME.

Using the script field

Cloud Build provides a script field that you can use to specify shell scripts to execute in a build step. The script field takes a single string value.

You can prefix the string value with a shebang to specify the shell to interpret the script. For example, add #!/usr/bin/env bash to specify the Bash shell. If you don't prefix the script string with a shebang, Cloud Build uses #!/bin/sh which is the basic sh shell, not Bash shell.

If you specify script in a build step, you cannot specify args or entrypoint in the same step.

The following snippet demonstrates the script field:

YAML

steps:
- name: bash
  script: |
    #!/usr/bin/env bash
    echo "Hello World"
- name: ubuntu
  script: echo hello
- name: python
  script: |
    #!/usr/bin/env python
    print('hello from python')

JSON

{
  "steps": [
  {
    "name": "bash",
    "script": "#!/usr/bin/env bash echo 'Hello World'"
  },
  {
    "name": "ubuntu",
    "script": "echo hello"
  },
  {
    "name": "python",
    "script": "#!/usr/bin/env python\nprint('hello from python')\n"
  }
  ]
}

Using substitutions with the script field

The script field does not support substitution variables. If you want to use substitutions, add them as environment variables using the env field.

The following snippet demonstrates how to set an environment variable using your project ID:

YAML

steps:
- name: ubuntu
  env:
  - 'BAR=$PROJECT_ID'
  script: 'echo $BAR'

JSON

{
  "steps": [
    {
      "name": "ubuntu",
      "env": [
        "BAR=$PROJECT_ID"
      ],
      "script": "echo $BAR"
    }
  ]
}

Running bash scripts on disk

If you have your bash script saved in a file, store the file along with your build source, and reference the script file within your build config file:

YAML

steps:
- name: 'bash'
  args: ['./myscript.bash']

JSON

{
  "steps": [
  {
    "name": "bash",
    "args": [
      "./myscript.bash"
     ]
  }
  ]
}

To use a bash script on file if bash is not the default entrypoint of the image you're using, add an entrypoint field pointing to bash:

YAML

steps:
- name: 'gcr.io/cloud-builders/gcloud'
  entrypoint: 'bash'
  args: ['tools/myScript.sh','--foo']

JSON

{
  "steps": [
  {
    "name": "gcr.io/cloud-builders/gcloud",
    "entrypoint": "bash",
    "args": [
      "tools/myScript.sh",
      "--foo"
    ]
  }
  ]
}

Running inline bash scripts (legacy)

To run bash commands using the bash image, specify bash as the name of the build step, and the command in the args field:

YAML

steps:
- name: 'bash'
  args: ['echo', 'I am running a bash command']

JSON

{
  "steps": [
    {
      "name": "bash",
      "args": [
        "echo",
        "I am running a bash command"
       ]
    }
  ]
}

If the image you're using comes prepackaged with bash but if bash is not the default entrypoint, add an entrypoint field pointing to bash. In the example below, the bash entrypoint is used to run gcloud commands that query Cloud Build for build status, listing builds with a failed status.

YAML

steps:
- name: 'gcr.io/google.com/cloudsdktool/cloud-sdk'
  entrypoint: 'bash'
  args:
  - '-eEuo'
  - 'pipefail'
  - '-c'
  - |-
    gcloud builds list > builds.txt
    while read line; do
        if grep -q "FAILURE" <<< "$line"; then
            echo "$line"
        fi
    done < builds.txt

JSON

{
  "steps": [
  {
    "name": "gcr.io/google.com/cloudsdktool/cloud-sdk",
    "entrypoint": "bash",
    "args": [
      "-eEuo",
      "pipefail",
      "-c",
      "gcloud builds list > builds.txt\nwhile read line; do\n    if grep -q \"FAILURE\" <<< \"$line\"; then\n        echo \"$line\"\n    fi\ndone < builds.txt"
    ]
  }
  ]
}

The -c flag in the code above is used to execute multi-line commands. Any string you pass after -c is treated as a command. For more information on running bash commands with -c, see the bash documentation.

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