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Expose stderr and stdout for commands #150

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Expose stderr and stdout for commands #150

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7 changes: 7 additions & 0 deletions lib/dry/cli.rb
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Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,10 @@ def call(arguments: ARGV, out: $stdout, err: $stderr)
# @api private
def perform_command(arguments)
command, args = parse(kommand, arguments, [])

command.instance_variable_set(:@stderr, err)
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@aaronmallen aaronmallen Jul 24, 2025 •
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The idea here is to not have to change the signature of Command#initialize causing a breaking change

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How about initializing a pair of StringIO in the command, and then

def perform_command(arguments)
  command, args = parse(kommand, arguments, [])
  command.call(**args)
  IO.copy_stream(command.out, out)
  IO.copy_stream(command.err, err)
end

This would make testing the stdout and stderr of commands much simpler.

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@aaronmallen aaronmallen Jul 25, 2025 •
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The intention is to utilize the out/err passed to the CLI in the first place. dry-cil uses them to print help and errors and "inline" commands. We should also allow the commands to use the user specified out/err. Testing is already trivial as the values are DI

command.instance_variable_set(:@stdout, out)

command.call(**args)
end

Expand All @@ -113,6 +117,9 @@ def perform_registry(arguments)

command, args = parse(result.command, result.arguments, result.names)

command.instance_variable_set(:@stderr, err)
command.instance_variable_set(:@stdout, out)

result.before_callbacks.run(command, args)
command.call(**args)
result.after_callbacks.run(command, args)
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33 changes: 33 additions & 0 deletions lib/dry/cli/command.rb
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Expand Up @@ -379,6 +379,39 @@ def self.superclass_options
optional_arguments
subcommands
] => "self.class"

protected

# The error output used to print error messaging
#
# @example
# class MyCommand
# def call
# stdout.puts "Hello World!"
# exit(0)
# rescue StandardError => e
# stderr.puts "Uh oh: #{e.message}"
# exit(1)
# end
# end
#
# @since unreleased
# @return [IO]
attr_reader :stderr

# The standard output object used to print messaging
#
# @example
# class MyCommand
# def call
# stdout.puts "Hello World!"
# exit(0)
# end
# end
#
# @since unreleased
# @return [IO]
attr_reader :stdout
end
end
end