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
Related
I want to scan unknown number of lines till all the lines are scanned. How do I do that in ruby?
For ex:
put returns between paragraphs
for linebreak add 2 spaces at end
_italic_ or **bold**
The input is not from a 'file' but through the STDIN.
Many ways to do that in ruby.
Most usually, you're gonna wanna process one line at a time, which you can do, for example, with
while line=gets
end
or
STDIN.each_line do |line|
end
or by running ruby with the -n switch, for example, which implies one of the above loops (line is being saved into $_ in each iteration, and you can addBEGIN{}, and END{}, just like in awk—this is really good for one-liners).
I wouldn't do STDIN.read, though, as that will read the whole file into memory at once (which may be bad, if the file is really big.)
Use IO#read (without length argument, it reads until EOF)
lines = STDIN.read
or use gets with nil as argument:
lines = gets(nil)
To denote EOF, type Ctrl + D (Unix) or Ctrl + Z (Windows).
I'm currently opening a file taken at runtime via ARGV:
File.open(ARGV[0]) do |f|
f.each_line do |line|
Once a match is found I print output to the user.
if line.match(/(strcpy)/i)
puts "[!] strcpy does not check for buffer overflows when copying to destination."
puts "[!] Consider using strncpy or strlcpy (warning, strncpy is easily misused)."
puts " #{line}"
end
I want to know how to print out the line number for the matching line in the (ARGV[0]) file.
Using print __LINE__ shows the line number from the Ruby script. I've tried many different variations of print __LINE__ with different string interpolations of #{line} with no success. Is there a way I can print out the line number from the file?
When Ruby's IO class opens a file, it sets the $. global variable to 0. For each line that is read that variable is incremented. So, to know what line has been read simply use $..
Look in the English module for $. or $INPUT_LINE_NUMBER.
We can also use the lineno method that is part of the IO class. I find that a bit more convoluted because we need an IO stream object to tack that onto, while $. will work always.
I'd write the loop more simply:
File.foreach(ARGV[0]) do |line|
Something to think about is, if you're on a *nix system, you can use the OS's built-in grep or fgrep tool to greatly speed up your processing. The "grep" family of applications are highly optimized for doing what you want, and can find all occurrences, only the first, can use regular expressions or fixed strings, and can easily be called using Ruby's %x or backtick operators.
puts `grep -inm1 abacus /usr/share/dict/words`
Which outputs:
34:abacus
-inm1 means "ignore character-case", "output line numbers", "stop after the first occurrence"
I was following the advice from this question when trying to read in multi-line input from the command line:
# change line separator
$/ = 'END'
answer = gets
pp answer
However, I get weird behavior from STDIN#gets when I try to change $/ back:
# put it back to normal
$/ = "\n"
answer = gets
pp answer
pp 'magic'
This produces output like this when executed with Ruby:
$ ruby multiline_input_test.rb
this is
a multiline
awesome input string
FTW!!
END
"this is\n\ta multiline\n awesome input string\n \t\tFTW!!\t\nEND"
"\n"
"magic"
(I input up to the END and the rest is output by the program, then the program exits.)
It does not pause to get input from the user after I change $/ back to "\n". So my question is simple: why?
As part of a larger (but still small) application, I'm trying to devise a way of recording notes; as it is, this weird behavior is potentially devastating, as the rest of my program won't be able to function properly if I can't reset the line separator. I've tried all manner of using double- and single-quotes, but that doesn't seem to be the issue. Any ideas?
The problem you're having is that your input ends with END\n. Ruby sees the END, and there's still a \n left in the buffer. You do successfully set the input record separator back to \n, so that character is immediately consumed by the second gets.
You therefore have two easy options:
Set the input record separator to END\n (use double quotes in order to have the newline character work):
$/ = "END\n"
Clear the buffer with an extra call to gets:
$/ = 'END'
answer = gets
gets # Consume extra `\n`
I consider option 1 clearer.
This shows it working on my system using option 1:
$ ruby multiline_input_test.rb
this is
a multiline
awesome input string
FTW!!
END
"this is\n a multiline\n awesome input string\n FTW!!\nEND\n"
test
"test\n"
"magic"
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
Often I find myself doing the following:
print "Input text: "
input = gets.strip
Is there a graceful way to do this in one line? Something like:
puts "Input text: #{input = gets.strip}"
The problem with this is that it waits for the input before displaying the prompt. Any ideas?
I think going with something like what Marc-Andre suggested is going to be the way to go, but why bring in a whole ton of code when you can just define a two line function at the top of whatever script you're going to use:
def prompt(*args)
print(*args)
gets
end
name = prompt "Input name: "
Check out highline:
require "highline/import"
input = ask "Input text: "
One liner hack sure. Graceful...well not exactly.
input = [(print 'Name: '), gets.rstrip][1]
I know this question is old, but I though I'd show what I use as my standard method for getting input.
require 'readline'
def input(prompt="", newline=false)
prompt += "\n" if newline
Readline.readline(prompt, true).squeeze(" ").strip
end
This is really nice because if the user adds weird spaces at the end or in the beginning, it'll remove those, and it keeps a history of what they entered in the past (Change the true to false to not have it do that.). And, if ARGV is not empty, then gets will try to read from a file in ARGV, instead of getting input. Plus, Readline is part of the Ruby standard library so you don't have to install any gems. Also, you can't move your cursor when using gets, but you can with Readline.
And, I know the method isn't one line, but it is when you call it
name = input "What is your name? "
Following #Bryn's lead:
def prompt(default, *args)
print(*args)
result = gets.strip
return result.empty? ? default : result
end
The problem with your proposed solution is that the string to be printed can't be built until the input is read, stripped, and assigned. You could separate each line with a semicolon:
$ ruby -e 'print "Input text: "; input=gets.strip; puts input'
Input text: foo
foo
I found the Inquirer gem by chance and I really like it, I find it way more neat and easy to use than Highline, though it lacks of input validation by its own.
Your example can be written like this
require 'inquirer'
inputs = Ask.input 'Input text'