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docs: Add documentation for new BASH syntax #6290

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docs: add documentation for new BASH syntax
sergio-costas Jun 12, 2026
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sergio-costas Jul 17, 2026
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Update snapcraft/models/project.py
sergio-costas Jul 23, 2026
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12 changes: 12 additions & 0 deletions snapcraft/models/project.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1858,6 +1858,18 @@ class Project(models.Project):
Environment variables are set at runtime for all apps. To set an
environment variable for a particular app, use the ``environment`` key for
that ``app`` entry.

With SnapD 2.77 and higher, this key supports Bash parameter expansions:

- Override the current value with ``${VAR:+override}``
- Fall back to a value with ``${VAR:-fallback}``
- Copy another variable's value with ``${VAR:+$OTHER_VAR}``
- Fall back to another variable's value with ``${VAR:-$OTHER_VAR}``

Nested braces such as ``${VAR:+${OTHER_VAR}}`` aren't supported.

To ensure this feature is available, use the ``assumes`` key to require a
minimum version of snapd, for example ``assumes: [snapd2.77]``.
Comment on lines +1871 to +1872

@medubelko medubelko Jul 22, 2026

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Suggested change
To ensure this feature is available, use the ``assumes`` key to require a
minimum version of snapd, for example ``assumes: [snapd2.77]``.
For parameter expansion, the ``assumes`` key must be set to a
minimum version of SnapD, such as ``[snapd2.77]``.

@sergio-costas sergio-costas Jul 23, 2026

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Maybe... "If parameter expansion is used, it is paramount to set the assumes key to version 2.77 or later (such as assumes: [snapd2.77])".

@bepri bepri Aug 3, 2026

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I think the word "paramount" feels a little too glittery. I don't like the "such as" in Michael's suggestion either, because it feels a suggestion that you can pin it to whatever version you want, so long as you're pinning it at all.

How about:

Suggested change
To ensure this feature is available, use the ``assumes`` key to require a
minimum version of snapd, for example ``assumes: [snapd2.77]``.
Since this feature requires a minimum version of SnapD, use the ``assumes`` key to
constrain your snap to a supported SnapD version with ``assumes: [snapd2.77]``.

"""

build_packages: Grammar[list[str]] | None = pydantic.Field(
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