将值附加到go中环境变量的现有值

Question

如何将另一个值附加到go环境变量的现有值？

如果CGO_CXXFLAGS 的值为“-I/blah/blah”

由于以下不起作用

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

我想找到一个正确的方法让CGO_CXXFLAGS具有值“-I/blah/blah -I/foo/bar”

通过避免简单地重新设置所有值加上新值，例如：

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

Answer 1

由于go env <var_name>&nbsp;输出变量的有效设置（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（假设是 Bash shell）：$&nbsp;(unset&nbsp;<var_name>;&nbsp;go&nbsp;env&nbsp;<var_name>)然后，要设置一个新值，您需要使用命令替换：$&nbsp;go&nbsp;env&nbsp;-w&nbsp;<var_name>="$(unset&nbsp;<var_name>;&nbsp;go&nbsp;env&nbsp;<var_name>)<value_to_append>"有关工作示例，请参阅以下带注释的日志：# Write an initial default.$ go env -w CGO_CXXFLAGS=-I/blah/blah$ go env CGO_CXXFLAGS-I/blah/blah# Keep in mind that the default can be overridden by a currently set&nbsp;# environment variable.$ export CGO_CXXFLAGS="-I/override/default"$ go env CGO_CXXFLAGS-I/override/default# To print the default value even when it is being overridden,# in a subshell, unset the environment variable and then run 'go env'.&nbsp;$ (unset CGO_CXXFLAGS; go env CGO_CXXFLAGS)-I/blah/blah# To set a new default value utilizing the existing default value.## Note: if the default isn't being overridden, no warning will be printed.$ go env -w CGO_CXXFLAGS="$(unset CGO_CXXFLAGS; go env CGO_CXXFLAGS) -I/foo/bar"warning: go env -w CGO_CXXFLAGS=... does not override conflicting OS environment variable# State after change...# Default value$ (unset CGO_CXXFLAGS; go env CGO_CXXFLAGS)-I/blah/blah -I/foo/bar# Overridden value$ go env CGO_CXXFLAGS-I/override/default或者，您可以找到具有默认值的文件并直接解析它（go env GOENV会告诉您文件位置），但我认为暂时取消设置环境变量并让其完成go env工作会更容易。PowerShell 中的等价物：# Write default.PS > go env -w CGO_CXXFLAGS=-I/blah/blahPS > go env CGO_CXXFLAGS-I/blah/blah# Override default.PS > $Env:CGO_CXXFLAGS = "-I/override/default"PS > go env CGO_CXXFLAGS-I/override/default# Print default.PS > Start-Job {$Env:CGO_CXXFLAGS=''; go env CGO_CXXFLAGS} | Receive-Job -Wait-I/blah/blah# Append to default.PS > go env -w CGO_CXXFLAGS="$(Start-Job {$Env:CGO_CXXFLAGS=''; go env CGO_CXXFLAGS} | Receive-Job -Wait) -I/foo/bar"warning: go env -w CGO_CXXFLAGS=... does not override conflicting OS environment variable# Final state.PS > go env CGO_CXXFLAGS-I/override/defaultPS > Start-Job {$Env:CGO_CXXFLAGS=''; go env CGO_CXXFLAGS} | Receive-Job -Wait-I/blah/blah -I/foo/bar