I have a beginners coding task, first step is my program "should prompt the user to enter a filename of a file that contains the following information:" There's already pre-made code to work on, a "music_player.rb" (where I have to write the code) and "albums.text" (which is the file I want to read from)
I know a_file = File.new("mydata.txt", "r") is to read from file. I'm trying to do:
file_name = gets()
a_file = File.new("#{file_name}" , "r") # (line 13)
I keep getting error
music_player_with_menu.rb:13:in `initialize': No such file or directory # rb_sysopen - albums.txt (Errno::ENOENT)
when I enter albums.txt. If I just remove gets and have File.new("albums.txt" , "r") it works. I'm not sure what I'm doing wrong.
Trying to read from mydata.txt\n is going to raise an exception unless the filename actually ends in \n, which is rarely the case. This is because you're using #gets, which includes the newline character(s) from the user pressing RETURN or ENTER.
When you read from STDIN, you will get a line-ending (e.g. \n on *nix, and \r\n on Windows). So, when you call #gets, you almost always need to call String#chomp on the result.
file_name = gets
#=> "foo\n"
file_name = gets.chomp
#=> "foo"
Related
Facing below issue eventhough the file is present in the folder.
H:\Ruby_test_works>ruby hurrah.rb
hurrah.rb:7:in `read': No such file or directory # rb_sysopen - H:/Ruby_
test_works/SVNFolders.txt (Errno::ENOENT)
from hurrah.rb:7:in `block in <main>'
from hurrah.rb:4:in `each_line'
from hurrah.rb:4:in `<main>'
Input file (input.txt) Columns are tab separated.
10.3.2.021.asd 10.3.2.041.def SVNFolders.txt
SubversionNotify Subversionweelta post-commit.bat
Commit message still rake customemail.txt
mckechney.com yahoo.in ReadMe.txt
Code :
dir = 'H:/Ruby_test_works'
file = File.open("#{dir}/input.txt", "r")
file.each_line do |line|
initial, final, file_name = line.split("\t")
#puts file_name
old_value = File.read("#{dir}/#{file_name}")
replace = old_value.gsub( /#{Regexp.escape(initial)}, #{Regexp.escape(final)}/)
File.open("#{dir}/#{file_name}", "w") { |fi| fi.puts replace }
end
I have tried using both forward and backward slashes but no luck. What I'm missing, not sure. Thanks.
puts file_name gives the below values
SVNFolders.txt
post-commit.bat
customemail.txt
ReadMe.txt
The file_name contains the newline character \n at the end, which won't get printed but messes up the path. You can fix the issue by stripping the line first:
initial, final, file_name = line.strip.split("\t")
When debugging code, be careful with puts. Quoting its documentation reveals an ugly truth:
Writes the given object(s) to ios. Writes a newline after any that do not already end with a newline sequence.
Another way to put this is to say it ignores (potential) newlines at the end of the object(s). Which is why you never saw that the file name actually was SVNFolders.txt\n.
Instead of using puts, you can use p when troubleshooting issues. The very short comparison between the two is that puts calls to_s and adds a newline, while p calls inspect on the object. Here is a bit more details about the differences: http://www.garethrees.co.uk/2013/05/04/p-vs-puts-vs-print-in-ruby/
Sometimes the issue is not the file, but the path to the file. Consider compare the file path with what you think the file path is with something like:
File.expand_path('my_file.rb')
I'm trying to read from a file, and because my more complex code doesn't work, I came back to basics to see whether it even reads properly.
My code:
MyParser.new(STDIN.read).run.lines.each do |line|
p line.chomp
end
I use
ruby program
(it's placed in a bin directory and I saved it without .rb )
Now program is waiting for me to write something. I type:
../examples/file.txt
and use CTRL + Z (I'm on Windows 10). It produces ^Z and I hit enter.
Now I have an error:
Invalid argument # rb_sysopen - ../examples/file.txt (Errno::EINVAL)
MyParser class and its whole logic works fine. I'll be grateful for any hints.
Without knowing, what your MyParser expect, it is hard to know, what you need.
But maybe this helps:
MyParser.new(STDIN.gets.strip).run.lines.each do |line|
p line.chomp
end
I would extend it by a message what you need:
puts "Please enter the filename"
STDOUT.flush
MyParser.new(STDIN.gets.strip).run.lines.each do |line|
p line.chomp
end
With STDOUT.flush the user gets the message, before STDIN.getswaits for a message.
In your case I would take a look on ARGV and call the program with:
ruby program ../examples/file.txt
Your program should then use:
MyParser.new(ARGV.first).run.lines.each do |line|
p line.chomp
end
Here is my code:
filename = ARGV.first
puts "We're gong to erase #{filename}"
puts "If you don't want that, hit CTRL-C (^C)."
puts "If you do want that, hit RETURN."
$stdin.gets
puts "Opening the file..."
target = open(filename, 'w')
puts "Truncating the file. Goodbye!"
target.truncate(0)
puts "Now I'm going to ask you for three lines."
print "line 1: "
line1 = $stdin.gets.chomp
print "line 2: "
line2 = $stdin.gets.chomp
print "line 3: "
line3 = $stdin.gets.chomp
puts "I'm going to write these to the file."
target.write(line1)
target.write("\n")
target.write(line2)
target.write("\n")
target.write(line3)
target.write("\n")
print target.read
puts "And finally, we close it."
target.close
I'm trying to get it to write and then read. It works if I do target.close and then target = open(filename) again at the bottom of the script. Is there another way?
I saw this post about python explaining you need to close a file after writing to it. Does this same thing apply to Ruby? Do I need to use flush?
Also should I be using parentheses after read and close? The example does not.
There's two ways to approach this. You can, as you've done, open the file for writing, write to it, close the file, and reopen it for reading. This is fine. Closing the file will flush it to disk and reopening it will put you back at the beginning of the file.
Alternatively you can open a file for both reading and writing and manually move around within the file, like a cursor in an editor. The options to do this are defined in IO.new.
The problem with your code is this.
target.write("\n")
print target.read
At this point you've been writing to the file. The target file pointer is pointing at the end of the file, like a cursor in an editor. When you target.read it's going to read the end of the file, so you get nothing. You'd have to go back to the beginning of the file first with rewind.
target.write("\n")
target.rewind
print target.read
You'll also have to open the file for reading and writing. w+ can do that, and truncate the file for you.
puts "Opening the file..."
target = File.open(filename, 'w+')
This is an advanced technique most often useful for when you want to hold a lock on a file during the whole reading and writing process to make sure nobody else can work on the file while you are. Generally you do this when you're reading and then writing. For example, if you had a counter in a file you want to read and then increment and make sure nobody can write between.
def read_and_update_counter
value = 0
# Open for reading and writing, create the file if it doesn't exist
File.open("counter", File::RDWR|File::CREAT, 0644) {|f|
# Get an exclusive lock to prevent anyone else from using the
# file while we're updating it (as long as they also try to flock)
f.flock(File::LOCK_EX)
# read the value
value = f.read.to_i
# go back to the beginning of the file
f.rewind
# Increment and write the new value
f.write("#{value + 1}\n")
# Flush the changes to the file out of the in-memory IO cache
# and to disk.
f.flush
# Get rid of any other garbage that might be at the end of the file
f.truncate(f.pos)
}
# File.open automatically closes the file for us
return value
end
3.times { puts read_and_update_counter }
So, I'm relatively new to programming, and I have started working with ruby. I am going through "Learn how to code the hard way: Ruby" and I am on exercise 15; the beginning of file reading. I have copied the code they provided word for word, literally copy and pasted it to make sure, but I am getting the same error. I've googled the error, but to no avail. I have the .rb file in the same directory as the .txt file I'm trying to read. Here is my code.
filename = ARGV.first
prompt = "> "
txt = File.open(filename)
puts "Here's your file: #{filename}"
puts txt.read()
puts "I'll also ask you to type it again:"
print prompt
file_again = STDIN.gets.chomp()
txt_again = File.open(file_again)
puts txt_again.read()
The error I keep getting it this:
ex15.rb:19:in 'initialize': No such file of directory - ex15.txt <Errno::ENOENT>
from ex15.rb:4:in 'open'
from ex15.rb:4:in '<main>'
command to run it:
ruby ex15.rb ex15.txt
Any help is appreciated. Thanks
When you don't specify the mode argument for File.open(), the default is 'r', which stands for read. And to read a file, it has to exist already. The error message is telling you that there is no file named 'ex15.txt' in the current directory for ruby to read.
To get rid of the error, create a file called ex15.txt in the current directory, and type 'hello world' in the file.
I'm new to Ruby, and I am writing a test program just to get some of the features down. Here is the program
#!/usr/bin/env ruby
class FileManager
def read_file(filename)
return nil unless File.exist?(filename)
File.read(filename)
end
end
if __FILE__ == $0
fm = FileManager.new
puts "What file would you like to open?"
fname = gets
puts fm.read_file fname
end
As you can see, it is very simple. If I comment the first line of the read_file method, I get this error
No such file or directory - /Users/macuser/Projects/Aptana\ Studio\ 3\ Workspace/Ruby\ Test/text (Errno::ENOENT)
from /Users/macuser/Projects/Aptana Studio 3 Workspace/Ruby Test/ruby.rb:6:in `read_file'
from /Users/macuser/Projects/Aptana Studio 3 Workspace/Ruby Test/ruby.rb:15:in `<main>'
when I run the program and use this file: /Users/macuser/Projects/Aptana\ Studio\ 3\ Workspace/Ruby\ Test/text
However, if I run cat /Users/macuser/Projects/Aptana\ Studio\ 3\ Workspace/Ruby\ Test/text, it outputs Hello, world!, as it should.
I don't believe it's a permissions issue because I own the folder, but just in case I've tried running the program as root. Also, I have made sure that fname is the actual name of the file, not nil. I've tried both escaped and unescaped versions of the path, along with just text or the full path. I know for a fact the file exists, so why is Ruby giving me this error?
With gets filename the filename includes a newline \n.
You have to remove it in your filename:
gets filename
p filename #"test.rb\n"
p File.exist?(filename) #false
p File.exist?(filename.chomp) #true
(And you don't need to mask the spaces)
It looks like you're shell-escaping your spaces even though gets does not go through a shell. You want to enter "/Users/macuser/Projects/Aptana Studio 3 Workspace/Ruby Test/text" instead of "/Users/macuser/Projects/Aptana\ Studio\ 3\ Workspace/Ruby\ Test/text".