The standalone V8 shell (d8) does not come with a console object, so I cannot do console.log. How do I print stuff to stdout?
Use the print function instead of console.log. For instance:
$ cat test.js
print('foo');
$ ~/src/v8/out/native/d8 test.js
foo
Head over to Sandeep Datta's blog post for more info on d8 helper functions like print.
Related
You can save code to a file and compile it with raku -c. Is there any way to do the same programatically, using some public API?
There is an undocumented named parameter :check to EVAL that will prevent the compiled code from actually running. It will return Nil on success. If there are any errors, it will throw like it otherwise also would.
$ raku -e 'q/say "foo"/.EVAL'
foo
$ raku -e 'q/zay "foo"/.EVAL'
===SORRY!=== Error while compiling ...
Undeclared routine:
zay used at line 1. Did you mean 'say'?
$ raku -e 'say q/say "foo"/.EVAL(:check)'
Nil
Perhaps that named parameter should be documented.
EDIT: Please note that this will not prevent BEGIN blocks from being run, as #ugexe pointed out.
The following code is a simplification of my current situation. I have a JSON log source which I continuously fetch and write to stdout with puts.
#!/usr/bin/env ruby
require "json"
loop do
puts({ value: "foobar" }.to_json)
sleep 1
end
I want to be able to pipe the output of this script into jq for further processing, but in a 'stream'-friendly way, using unix pipes. Running the above code like so:
./my_script | jq
Results in an empty output. However, if I place an exit statement after the sleep call, the output is sent through the pipe to jq as expected. I was able to solve this problem by calling $stdout.flush following the puts call. While it's working now, I'm not sure why. $stdout.sync is set to true by default (see IO#sync). It seems to me that if sync was enabled, then Ruby should be doing no output buffering, and calling $stdout.flush should not be required - yet it is.
My follow-up question is about using tail instead of jq. It seems to me that I should be able to pipe a text stream into tail the same way I pipe it into jq, but neither method (with the $stdout.flush call or without it) works - the output is just empty.
As #Ry points out in the comments, $stdout.sync is true by default in IRB, but this is not necessarily the same for scripts.
So you should set $stdout.sync = true to be sure to prevent buffering.
If I run code like this, I get - in the __FILE__ var:
cat script.rb | ruby
I can't find that documented anywhere though (docs). Where can I get exact details about it?
- is sometimes used to refer to STDIN. This is a unix thing, and not unique to ruby.
Described a little bit here
I'm using pry and I want to capture, and work with output of a shell command.
For example, If I run
pry(main)> .ls
I want to get the list of files into an array that I can work with in Ruby.
How can I do this?
This is a pretty old question but I'll answer it anyways. There are two primary methods of getting data out of pry commands. The first is if the command sets the keep_retval option to true, which the shell command does not. The second, is to use the virtual pipe. In your example this can be done as:
fizz = []
.ls | {|listing| fizz = listing.split("\n")} # can also be written as
.ls do |listing|
fizz = listing.split("\n")
end
I assume it's some kind of pry's magic ;-)
After quick look at what's happening (I didn't look at pry's source), you might want to use this:
`ls`.split("\n")
or
Dir['./*']
What's good about this solution is that it will work outside of pry
I'm working on implementing Project Euler solutions as semantic Ruby one-liners. It would be extremely useful if I could coerce Ruby to automatically puts the value of the last expression. Is there a way to do this? For example:
#!/usr/bin/env ruby -Ilib -rrubygems -reuler
1.upto(100).into {|n| (n.sum.squared - n.map(&:squared).sum)
I realize I can simply puts the line, but for other reasons (I plan to eval the file in tests, to compare against the expected output) I would like to avoid an explicit puts. Also, it allots me an extra four characters for the solution. :)
Is there anything I can do?
You might try running it under irb instead of directly under a Ruby interpreter.
It seems like the options -f --noprompt --noverbose might be suitable (.
#!/usr/bin/env irb -f --noprompt --noverbose -Ilib -rrubygems -reuler
'put your one-liner here'
The options have these meanings:
-f: do not use .irbrc (or IRBRC)
--noverbose: do not display the source lines
--noprompt: do not prefix the output (e.g. with =>)
result = calculate_result
puts result if File.exist?(__FILE__)
result of eval is last executed operation just like any other code block in ruby
is doing
puts eval(file_contents)
an option for you?
EDIT
you can make use of eval's second parameter which is variables binding
try the following:
do_not_puts = true
eval(file_contents, binding)
and in the file:
....
result = final_result
if defined?(do_not_puts)
result
else
puts(result)
end
Is it an option to change the way you run scripts?
script.rb:
$_= 1.upto(100).into {|n| (n.sum.squared - n.map(&:squared).sum)
invoke with
echo nil.txt | /usr/bin/env/ruby -Ilib -rrubygems -reuler -p script.rb, where nil.txt is a file with a single newline.