尝试用ruby popen3检查命令是否存在

Question

我试图用以下代码检查system命令是否存在：

require 'open3'

Open3.popen3('non-existing command') do |stdin, stdout, stderr, thread|
  exit_error = stderr.readlines
  if exit_error["No such file or directory"]
    puts "command not found"
  end
end

但是，它只是带着下面的错误消息崩溃，没有继续：

/home/pavel/.rvm/rubies/ruby-2.0.0-p247/lib/ruby/2.0.0/open3.rb:211:in `spawn': No such file or directory - non-existing (Errno::ENOENT)

为什么以及如何修复它？

Answer 1

如果Open3.popen3找不到命令，它就会引发Errno::ENOENT异常；因此，您只需从该异常中拯救：

require 'open3'

begin
  Open3.popen3('non-existing command') do |stdin, stdout, stderr, thread|
  end
rescue Errno::ENOENT
  puts "command not found"
end

#=> outputs "command not found"