Question

my Question is how I can convert the STDIN of cmd ARGV or gets from hex to ascii

I know that if I assigned hex string to variable it’ll be converted once I print it

ex

hex_var = "\x41\41\x41\41"
puts hex_var

The result will be

AAAA

but I need to get the value from command line by (ARGV or gets)

say I’ve this lines

s = ARGV

puts s
# another idea
puts s[0].gsub('x' , '\x')

then I ran

ruby  gett.rb \x41\x41\x41\x41 

I got

\x41\x41\x41\x41

is there a way to get it work ?

Answer 1

There are a couple problems you’re dealing with here. The first you’ve already tried to address, but I don’t think your solution is really ideal. The backslashes you’re passing in with the command line argument are being evaluated by the shell, and are never making it to the ruby script. If you’re going to simply do a gsub in the script, there’s no reason to even pass them in. And doing it your way means any ‘x’ in the arguments will get swapped out, even those that aren’t being used to indicate a hex. It would be better to double escape the \ in the argument if possible. Without context of where the values are coming from, it’s hard to say with way would actually be better.

ruby gett.rb \\x41\\x41

That way ARGV will actually get ‘\x41\x41’, which is closer to what you want.

It’s still not exactly what you want, though, because ARGV arguments are created without expression substitution (as though they are in single quotes). So Ruby is escaping that \ even though you don’t want it to. Essentially you need to take that and re-evaluate it as though it were in double quotes.

eval('"%s"' % s)

where s is the string.

So to put it all together, you could end up with either of these:

# ruby gett.rb \x41\x41

ARGV.each do |s|
  s = s.gsub('x' , '\x')
  p eval('"%s"' % s)
end
# => "AA"

# ruby gett.rb \\x41\\x41

ARGV.each do |s|
  p eval('"%s"' % s)
end
# => "AA"