在文件路径中使用环境变量

Question

I want to use an input path in the following code:

File.exists?(File.expand_path(path))

Can I use environment variables in path , and what should the syntax be?

Answer 1

You can use standard ruby string interpolation (though it's a little bit wordy)

path = "log/#{ENV['RAILS_ENV']}.log" # or whatever
# >> "log/development.log"

Answer 2

To expand environment variables, you should do it yourself:

def expand_env(str)
  str.gsub(/\$([a-zA-Z_][a-zA-Z0-9_]*)|\${\g<1>}|%\g<1>%/) { ENV[$1] }
end

expand_env("${SHELL}:%USER%:$PAGER")
# => "/bin/bash:amadan:less"

(both Windows-style and Unix-style are supported, but only the basic substitution, and not any crazy stuff that bash is capable of).

Answer 3

为了便于携带，最好使用File::join和ENV Hash：

File.exists?( File.join(ENV['MY_VAR'],'bin') )