I'm a Ruby newbie, I tried to print each char in a Ruby string, using
"hello world".each_char {|c| print c}
However, when I ran the .rb program, it printed out hello world%, with a % character at the end. Then I switched to irb, it worked fined without the extra % character. Can anyone tell me how this happened? Why there was a %?
the program is doing what is expected.
the % is actually the shell prompt.
guessing you do something like:
%my-script.rb
hello world%
because you don't have a new line, when the output finishes the script just takes control back and shows the prompt
Related
How do I add a line-break/new-line in IRB/Ruby? The book I'm learning from shows this code:
print "2+3 is equal to "
print 2 + 3
without telling how to go to the second line without hitting Enter, which obviously just runs the program.
You could use semicolon at the end of statement like this puts "hello";puts"world"
That book might be taking very tiny steps to introducing this idea:
print "Continues..."
puts "(Up to here)"
The print function just outputs to the terminal exactly what it's given. The puts function does the same but also adds a newline, which is what you want.
The more Ruby way of doing this is either:
puts "2+3 equals #{2+3}" # Using string interpolation
puts "2+3 equals %d" % (2 + 3) # Using sprintf-style interpolation
Now if you're using irb, that's a Read-Evaluate-Print-Loop (REPL) which means it executes everything you type in as soon as you press enter, by design. If you want to use your original code, you need to force it on one line:
print "2+3 equals "; print 2+3
Then that will work as expected. The ; line separator is rarely used in Ruby, most style guides encourage you to split things up onto multiple lines, but if you do need to do a one-liner, this is how.
When writing code in, say a .rb file the return key is just used for formatting and doesn't execute any code.
You can put a semicolon after the first line, like this:
print "2+3 is equal to ";
print 2 + 3
I try to run an external command in Ruby, and parse its output .
IO.popen(command, :err=>[:child, :out]) {|ls_io|
ls_io.each do |line|
print line
end
}
This way of doing it works wonders… except when I parse the progress-output of a c-program that shows it progress to stdout with \r.
As long as the c-program has not outputted a \n (that is as long as it has not finished some long-operation), Ruby waits and sees nothing. Then when a \n is outputted, Ruby sees it all
1%\r2%\r3%\r…100%
task finished
I tried all of the many ways to call external commands (eg Calling shell commands from Ruby) ; but none seem to capture the progress. I also tried every opeartor such as STDOUT.sync = true, and the c-program does call fflush(stdout)
I finally found a workaroud. I do :
IO.popen(commande, :err=>[:child, :out]) {|ls_io|
while true
byte=ls_io.read(1)
if byte.nil?
break
end
print byte
end
}
It's stupid… but it works.
Any more elegant way, and much more efficient way to do this ? Performance is terrible, as if the "refresh rate" was slow.
Set the input record separator to "\r" right before your block (provided you know it in advance):
$/ = "\r"
Reference of global preset variables: http://www.zenspider.com/Languages/Ruby/QuickRef.html#pre-defined-variables
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 ?
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"
Backlashes entered in the console will be interpreted by the shell and will
not make it into your Ruby script, unless you enter two backlashes in a row,
in which case you script will get a literal backlash and no automatic
conversion of hexadecimal character codes following those backlashes.
You can convert these escaped codes to characters manually if you replace the last line of your script with this:
puts s.gsub(/\\x([[:xdigit:]]{1,2})/) { $1.hex.chr }
Then run it with double backlashed input:
$ ruby gett.rb \\x41\\x42\\x43
ABC
When fetching user input through gets or similar, only a single backslash will be need to be entered by the user for each character escape, since that will indeed be passed to your script as literal backslashes and thus handled correctly by the above gsub call.
An alternative way when parsing command line arguments would be to let the shell interpret the character escapes for you. How to do this will depend on what shell you are using. If using bash, it can be done
like this:
$ echo $'\x41\x42\x43'
ABC
$ ruby -e 'puts ARGV' $'\x41\x42\x43'
ABC
I'm a bit confused with the input's of Ruby.
Whenever I try to get input, it doesn't register the 'Backspace' key. Also, it never accepts the 'Enter' first time. I always have to push 'Enter' after my input usually 3 times before it actually inputs it.
For example,
view source
print?
1 my_var = gets.chomp
If I wanted to enter 'Hello', I would have to type it followed by pressing the return key 3 times before it actually entered it.
Now I did find a way to solve this using...
view source
print?
1 STDOUT.flush
2 my_var = gets.chomp
But...
1) This seems wierd having to enter that EVERY time before I want input?
2) It still doesn't solve the problem of registering backspace.
If I was to type directly 'Hello World' but with two accidental keystrokes such as this: Hello Worpold
Even if I used the backspace so it appeared as I was entering: Hello World
If I then went on to 'puts' or 'print' that it would output: Hello Worpold
Know how I can fix it so it accepts backspace and know any other ways of missing out STDOUT.flush?
Thanks in advance
Use the readline module.
What environment are you running Ruby in ? If you're unsure, check with ruby -v
>ruby -v
ruby 1.8.6 (2008-08-11 patchlevel 287) [i386-mswin32]
I'm running v1.8.6 on Windows XP
a = gets
puts "I just got #{a}"
Saved the above snippet to c:\temp.rb and run it with ruby c:\temp.rb
Backspace key works, I can correct strings before pressing enter once to confirm my input.
If I say
puts "Hello"
and decide to add an extra newline I need to do this:
puts "Hello\n"
Having this character in the string is ugly. Is there any way to do this without polluting my string?
Just make another call to puts:
puts "Hello"
puts
puts "Hello",""
I often find myself adding a constant in ruby to contain these characters
NEW_LINE = "\n"
puts "Hello" + NEW_LINE
I think it is more readable and makes a change to all newline characters easy if anyone ever decides to separate each line by something else at some later date.
Do you think this looks nicer?
puts "Hello"+$/
</evil>
The reason Ruby uses "\n" for a newline is because its based on C. Ruby MRI is written in C and even JRuby is written in Java which is based on C++ which is based on C... you get the idea! So all these C-style languages use the "\n" for the new line.
You can always write your own method that acts like puts but adds new lines based upon a parameter to the method.
you can just write
p "Hello"
p
That should work as well if you want to keep it short and simple
Well, I don't think an explicit newline is ugly. mipadi's answer is just fine as well. Just to throw another answer in, make an array of the lines then join the aray with a newline. :)
What you want fixed:
input for script:
puts "Hello there"
puts "Goodbye"
Output from script:
Hello thereGoodbye
Fix for the problem:
Input for script:
puts "Hello there"
puts
puts "Goodbye"
Output from script:
Hello there
Goodbye