So I am studying Build Awesome Command-Line Applications in Ruby. On page 81, we're supposed to use STDIN to enter more than one task into a project.
File.open(global_options[:filename], 'a+') do |todo_file|
if task_names.empty?
puts "Reading new tasks from stdin..."
task_names = STDIN.readlines.map {|a| a.chomp}
end
tasks = 0
task_names.each do |task|
todo_file.puts [task, Time.now].join(', ')
tasks+=1
end
if tasks == 0
raise "You must provide tasks on the command-line or standard input"
end
end
The usual way to enter tasks into a project it's like this $todo new "Rake leaves but with the code above we can to what's in the example below.
It does work. But how do I tell STDIN to stop listening? The example on how to use it is this...
$ todo new
Rake leaves
Take out trash
Clean garage
Put away dishes
^D
What does the ^D represent?
It’s an end-of-file character. You can type this literally on Unix systems with Ctrl+D or on Windows with Ctrl+Z. The traditional way of displaying the Ctrl modifier is with a ^ prefix, e.g., ^D.
Be aware that this closes standard input entirely. If you want to read more data after entering these lines, you’ll need to check the input itself for a different delimiter—for instance, an empty line.
You can close STDIN by pressing Ctrl-d on Unix-like systems or Ctrl-z on Windows.
What does the ^6 represent?
Are you sure it says ^6 and not ^d? If so, that's probably a typo.
Related
I am writing a program in which I am taking in a csv file via the < operator on the command line. After I read in the file I would also like to ask the user questions and have them input their response via the command line. However, whenever I ask for user input, my program skips right over it.
When I searched stack overflow I found what seems to be the python version here, but it doesn't really help me since the methods are obviously different.
I read my file using $stdin.read. And I have tried to use regular gets, STDIN.gets, and $stdin.gets. However, the program always skips over them.
Sample input ruby ./bin/kata < items.csv
Current File
require 'csv'
n = $stdin.read
arr = CSV.parse(n)
input = ''
while true
puts "What is your choice: "
input = $stdin.gets.to_i
if input.zero?
break
end
end
My expected result is to have What is your choice: display in the command and wait for user input. However, I am getting that phrase displayed over and over in an infinite loop. Any help would be appreciated!
You can't read both file and user input from stdin. You must choose. But since you want both, how about this:
Instead of piping the file content to stdin, pass just the filename to your script. The script will then open and read the file. And stdin will be available for interaction with the user (through $stdin or STDIN).
Here is a minor modification of your script:
arr = CSV.parse(ARGF) # the important part.
input = ''
while true
puts "What is your choice: "
input = STDIN.gets.to_i
if input.zero?
break
end
end
And you can call it like this:
ruby ./bin/kata items.csv
You can read more about ARGF in the documentation: https://ruby-doc.org/core-2.6/ARGF.html
This has nothing to do with Ruby. It is a feature of the shell.
A file descriptor is connected to exactly one file at any one time. The file descriptor 0 (standard input) can be connected to a file or it can be connected to the terminal. It can't be connected to both.
So, therefore, what you want is simply not possible. And it is not just not possible in Ruby, it is fundamentally impossible by the very nature of how shell redirection works.
If you want to change this, there is nothing you can do in your program or in Ruby. You need to modify how your shell works.
I want to write a command in the terminal like config.section.key, parse the command, and get the strings "section" and "key". I want to use these two keys in my function to search a hash.
Is there any way to parse a command from the terminal to do this?
To execute terminal commands you can use either backticks or a system call here's some examples keep in mind that this is all pseudo code and I have no idea if this will run correctly:
def create_file
`touch test.txt`
end
def cmd
system('ls')
end
def check_file
results = cmd
if results.include?('test.txt')
puts 'File exists.'
else
puts 'Creating file..'
create_file
end
end
Now to the parsing part, depending on what you want to do, you can either save the information into a variable, or you could use a regex to extract the information. So if you wanted to extract digits with a regex: /\d+/ if you wanted to save the information: results = cmd..
I hope this answers your question.
To split the information, you could use the split method for example:
def cmd
`prt_jobs`
end
def check_jobs
res = cmd
res.split(".")
end
This will split the results of a print jobs command by periods and make them into an array. I'd show you more except I'm on my phone so it will have to wait
As Tadman commented, you can use the String#split method to split the argv on period characters, if that is your desire:
config, section, key, *rest = ARGF.argv.split('.')
Another good option when dealing with parsing command lines is the Ruby standard library OptionParser class. Rather than rebuild all of the CLI parsing by hand, the OptionParser class has that built in and much more. The resulting scripts can feel much more linux like and be familiar to anyone who's used bash before.
I am writing a program which execute an other program written in c, here is my first try
require 'Open3'
system 'tcc temp.c'
Open3.popen3('temp.exe') do |stdin, stdout, stderr|
stdin.puts '21\n'
STDOUT.puts stdout.gets
end
actual output:
Enter the temperature in degrees fahrenheit: The converted temperature is -6.11
desired output:
Enter the temperature in degrees fahrenheit: 21
The converted temperature is -6.11
and if you know a better way to do that please tell me, i am new to ruby.
You seem to have at least two potential issues:
Your newline will not expand inside single quotes. To include a newline within a string, you need to use double-quotes such as "21\n".
In some cases, you actually need a carriage return rather than a newline. This is especially true when trying to do Expect-like things with a terminal. For example, you may find you need \r instead of \n in your string.
You definitely need to fix the first thing, but you may need to try the second as well. This is definitely one of those "your mileage may vary" situations.
It seems like you're expecting 21 to appear on your screen because it does when you run temp.exe and type in 21. The reason it appears on your screen under those circumstances is that you're typing them into your shell, which "echoes" back everything you type.
When you run the program via Ruby, though, there's no shell and no typing, so 21 doesn't appear on your screen even though it's correctly being sent to the program's standard input.
The simplest solution is pretty simple. Just write it to Ruby's standard output as well:
require 'Open3'
system 'tcc temp.c'
Open3.popen3('temp.exe') do |stdin, stdout, stderr|
STDOUT.puts "21"
stdin.puts '"21"
STDOUT.puts stdout.gets
end
(You'll note that I took out \n—IO#puts adds that for you.)
This is a little repetitive, though. You might define a simple method to take care of it for you:
def echo(io, *args)
puts *args
io.puts *args
end
Then:
Open3.popen3('temp.exe') do |stdin, stdout, stderr|
echo(stdin, "21")
puts stdout.gets
end
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
I have a Ruby script (1.8.7) that sets up its own interactive shell for running specific commands.
I want to be able to exit when a user presses CTRL+D (mac/linux). The script just sits in a loop and uses Readline to read user input. I understand that CTRL+D sends the EOF control character but how do I test for this in Ruby? It doesn't seem to be included in the lists of standard unix signals and since technically it isn't a character, I'm guessing normal string comparison on the line won't work either.
Any ideas / pointers / suggestions would be much appreciated
Cheers
From the documentation:
readline(prompt = "", add_hist = false)
(…) Returns nil when the inputted line is empty and user inputs EOF (Presses ^D on UNIX).
Example:
require "readline"
while buf = Readline.readline("> ", true)
p buf
end
puts "EOF received, exiting"