Appending values to existing values of environment variables in go

huangapple
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英文:

Appending values to existing values of environment variables in go

问题

如何将另一个值追加到现有的 go 环境变量的值中？

如果 CGO_CXXFLAGS 的值为 "-I/blah/blah"

由于以下方法不起作用

  1. $ go env -w CGO_CXXFLAGS="$CGO_CXXFLAGS -I/foo/bar"

我想找到一种合适的方法，使 CGO_CXXFLAGS 的值为 "-I/blah/blah -I/foo/bar"

而不是简单地重新设置所有的值加上新的值，例如：

  1. $ go env -w CGO_CXXFLAGS="-I/blah/blah -I/foo/bar"
英文:

How can I append another value to an existing value of a go environment variable?

If CGO_CXXFLAGS has the value "-I/blah/blah"

Since the following doesn't work

  1. $ go env -w CGO_CXXFLAGS="$CGO_CXXFLAGS -I/foo/bar"

I want to find a proper way to CGO_CXXFLAGS have the value "-I/blah/blah -I/foo/bar"

by avoiding to simply re-set all the values plus the new one, such as in:

  1. $ go env -w CGO_CXXFLAGS="-I/blah/blah -I/foo/bar"

答案1

得分: 3

由于go env <var_name>输出的是变量的有效设置（即不一定是默认值），获取环境变量当前默认值的可靠方法是使用子shell（假设使用Bash shell）：

  1. $ (unset <var_name>; go env <var_name>)

然后，要设置新值，您可以使用命令替换：

  1. $ go env -w <var_name>="$(unset <var_name>; go env <var_name>)<value_to_append>"

请参考以下带注释的日志，了解一个工作示例：

  1. # 写入初始默认值。
  2. $ go env -w CGO_CXXFLAGS=-I/blah/blah
  4. $ go env CGO_CXXFLAGS
  5. -I/blah/blah
  7. # 请记住，默认值可能被当前设置的环境变量覆盖。
  8. $ export CGO_CXXFLAGS="-I/override/default"
  10. $ go env CGO_CXXFLAGS
  11. -I/override/default
  13. # 要打印默认值，即使它被覆盖了，在子shell中取消设置环境变量，然后运行'go env'。
  14. $ (unset CGO_CXXFLAGS; go env CGO_CXXFLAGS)
  15. -I/blah/blah
  17. # 要设置新的默认值，利用现有的默认值。
  18. #
  19. # 注意：如果默认值没有被覆盖，将不会打印警告。
  20. $ go env -w CGO_CXXFLAGS="$(unset CGO_CXXFLAGS; go env CGO_CXXFLAGS) -I/foo/bar"
  21. warning: go env -w CGO_CXXFLAGS=... does not override conflicting OS environment variable
  23. # 更改后的状态...
  24. # 默认值
  25. $ (unset CGO_CXXFLAGS; go env CGO_CXXFLAGS)
  26. -I/blah/blah -I/foo/bar
  28. # 被覆盖的值
  29. $ go env CGO_CXXFLAGS
  30. -I/override/default

或者，您可以找到默认值的文件并直接解析它（go env GOENV将告诉您文件位置），但我认为暂时取消设置环境变量并让go env完成工作更容易。

在PowerShell中的等效方法：

  1. # 写入默认值。
  2. PS > go env -w CGO_CXXFLAGS=-I/blah/blah
  3. PS > go env CGO_CXXFLAGS
  4. -I/blah/blah
  6. # 覆盖默认值。
  7. PS > $Env:CGO_CXXFLAGS = "-I/override/default"
  8. PS > go env CGO_CXXFLAGS
  9. -I/override/default
  11. # 打印默认值。
  12. PS > Start-Job {$Env:CGO_CXXFLAGS=''; go env CGO_CXXFLAGS} | Receive-Job -Wait
  13. -I/blah/blah
  15. # 追加到默认值。
  16. PS > go env -w CGO_CXXFLAGS="$(Start-Job {$Env:CGO_CXXFLAGS=''; go env CGO_CXXFLAGS} | Receive-Job -Wait) -I/foo/bar"
  17. warning: go env -w CGO_CXXFLAGS=... does not override conflicting OS environment variable
  19. # 最终状态。
  20. PS > go env CGO_CXXFLAGS
  21. -I/override/default
  23. PS > Start-Job {$Env:CGO_CXXFLAGS=''; go env CGO_CXXFLAGS} | Receive-Job -Wait
  24. -I/blah/blah -I/foo/bar

以上是您提供的内容的翻译。

英文:

Since go env &lt;var_name&gt; outputs the effective setting of the variable (i.e. not necessarily the default value), a reliable way to get at the current default value of an environment variable is using a subshell (assuming a Bash shell):

  1. $ (unset &lt;var_name&gt;; go env &lt;var_name&gt;)

And then, to set a new value you'd want to use command substitution:

  1. $ go env -w &lt;var_name&gt;=&quot;$(unset &lt;var_name&gt;; go env &lt;var_name&gt;)&lt;value_to_append&gt;&quot;

See the following annotated log for a working example:

  1. # Write an initial default.
  2. $ go env -w CGO_CXXFLAGS=-I/blah/blah
  4. $ go env CGO_CXXFLAGS
  5. -I/blah/blah
  7. # Keep in mind that the default can be overridden by a currently set 
  8. # environment variable.
  9. $ export CGO_CXXFLAGS=&quot;-I/override/default&quot;
  11. $ go env CGO_CXXFLAGS
  12. -I/override/default
  14. # To print the default value even when it is being overridden,
  15. # in a subshell, unset the environment variable and then run &#39;go env&#39;. 
  16. $ (unset CGO_CXXFLAGS; go env CGO_CXXFLAGS)
  17. -I/blah/blah
  19. # To set a new default value utilizing the existing default value.
  20. #
  21. # Note: if the default isn&#39;t being overridden, no warning will be printed.
  22. $ go env -w CGO_CXXFLAGS=&quot;$(unset CGO_CXXFLAGS; go env CGO_CXXFLAGS) -I/foo/bar&quot;
  23. warning: go env -w CGO_CXXFLAGS=... does not override conflicting OS environment variable
  25. # State after change...
  26. # Default value
  27. $ (unset CGO_CXXFLAGS; go env CGO_CXXFLAGS)
  28. -I/blah/blah -I/foo/bar
  30. # Overridden value
  31. $ go env CGO_CXXFLAGS
  32. -I/override/default

Alternatively, you could find the file with the defaults and parse it directly (go env GOENV will tell you the file location), but I think it's easier to temporarily unset the environment variable and let go env do the work.

Equivalent in PowerShell:

  1. # Write default.
  2. PS &gt; go env -w CGO_CXXFLAGS=-I/blah/blah
  3. PS &gt; go env CGO_CXXFLAGS
  4. -I/blah/blah
  6. # Override default.
  7. PS &gt; $Env:CGO_CXXFLAGS = &quot;-I/override/default&quot;
  8. PS &gt; go env CGO_CXXFLAGS
  9. -I/override/default
  11. # Print default.
  12. PS &gt; Start-Job {$Env:CGO_CXXFLAGS=&#39;&#39;; go env CGO_CXXFLAGS} | Receive-Job -Wait
  13. -I/blah/blah
  15. # Append to default.
  16. PS &gt; go env -w CGO_CXXFLAGS=&quot;$(Start-Job {$Env:CGO_CXXFLAGS=&#39;&#39;; go env CGO_CXXFLAGS} | Receive-Job -Wait) -I/foo/bar&quot;
  17. warning: go env -w CGO_CXXFLAGS=... does not override conflicting OS environment variable
  19. # Final state.
  20. PS &gt; go env CGO_CXXFLAGS
  21. -I/override/default
  23. PS &gt; Start-Job {$Env:CGO_CXXFLAGS=&#39;&#39;; go env CGO_CXXFLAGS} | Receive-Job -Wait
  24. -I/blah/blah -I/foo/bar

huangapple
  • 本文由 发表于 2022年5月7日 14:15:37
  • 转载请务必保留本文链接：https://go.coder-hub.com/72149968.html
  • environment-variables
  • go
  • shell
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