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Merge pull request #84 from nVitius/var-interpolation-docs 

Document Compose's syntax for variable defaults
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Victoria Bialas 2016-10-31 13:43:32 -07:00 committed by GitHub
parent 089462d7c7 980956ef9d
commit 1676a8478d
1 changed files with 14 additions and 2 deletions
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@ -1143,8 +1143,20 @@ string. In the example above, if `EXTERNAL_PORT` is not set, the value for the
port mapping is `:5000` (which is of course an invalid port mapping, and will port mapping is `:5000` (which is of course an invalid port mapping, and will
result in an error when attempting to create the container). result in an error when attempting to create the container).
Both `$VARIABLE` and `${VARIABLE}` syntax are supported. Extended shell-style In the case of environment variables that are not set, it is also possible to
features, such as `${VARIABLE-default}` and `${VARIABLE/foo/bar}`, are not define default values using one of the following syntax variants:
* To provide a default value that will be used if `VARIABLE` is either *unset* or *empty*:
`${VARIABLE:-default}`
* To provide a default value only if `VARIABLE` is *empty*:
`${VARIABLE-default}`
Both `$VARIABLE` and `${VARIABLE}` syntax are supported. Extended
shell-style features, such as `${VARIABLE/foo/bar}`, are not
supported. supported.
You can use a `$$` (double-dollar sign) when your configuration needs a literal You can use a `$$` (double-dollar sign) when your configuration needs a literal