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38 lines
1.5 KiB
Markdown
38 lines
1.5 KiB
Markdown
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envflag
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=======
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Golang flags, but bolted onto the environment rather than the command-line.
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Read the [godocs](http://godoc.org/github.com/ianschenck/envflag).
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Motivation
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==========
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Some like the distinction that command-line flags control behavior
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while environment variables configure. Also
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[12-factor](http://12factor.net/) recommends the use of environment
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variables for configuration. The interface of the golang flag package
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is well designed and easy to use, and allows for other lists
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(os.Environ() vs os.Args) to be parsed as flags. It makes sense then
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to use the same interface, the same types, and the same parsing
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(caveat: there is some ugly string hacking to make environment
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variables look like flags) to the same ends.
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Differences
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===========
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Calling `flag.Parse()` will not parse environment flags. Calling
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`envflag.Parse()` will not parse command-line flags. There is no good
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reason to combine these two when the net savings is a single line in a
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`func main()`. Furthermore, doing so would require users to accept a
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precedence order of my choosing.
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The presence of an environment variable named `h` or `help` will
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probably cause problems (print Usage and os.Exit(0)). Work around this
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by defining those flags somewhere (and ignoring them).
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Before calling `Flagset.Parse` on `EnvironmentFlags`, the environment
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variables being passed to `Parse` are trimmed down using
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`Lookup`. This behavior is different from `flag.Parse` in that extra
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environment variables are ignored (and won't crash `envflag.Parse`).
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