I need to read the data out of database and then save it in a text file.
How can I do that in Ruby? Is there any file management system in Ruby?
Are you looking for the following?
File.open(yourfile, 'w') { |file| file.write("your text") }
You can use the short version:
File.write('/path/to/file', 'Some glorious content')
It returns the length written; see ::write for more details and options.
To append to the file, if it already exists, use:
File.write('/path/to/file', 'Some glorious content', mode: 'a')
This is preferred approach in most cases:
File.open(yourfile, 'w') { |file| file.write("your text") }
When a block is passed to File.open, the File object will be automatically closed when the block terminates.
If you don't pass a block to File.open, you have to make sure that file is correctly closed and the content was written to file.
begin
file = File.open("/tmp/some_file", "w")
file.write("your text")
rescue IOError => e
#some error occur, dir not writable etc.
ensure
file.close unless file.nil?
end
You can find it in documentation:
static VALUE rb_io_s_open(int argc, VALUE *argv, VALUE klass)
{
VALUE io = rb_class_new_instance(argc, argv, klass);
if (rb_block_given_p()) {
return rb_ensure(rb_yield, io, io_close, io);
}
return io;
}
The Ruby File class will give you the ins and outs of ::new and ::open but its parent, the IO class, gets into the depth of #read and #write.
Zambri's answer found here is the best.
File.open("out.txt", '<OPTION>') {|f| f.write("write your stuff here") }
where your options for <OPTION> are:
r - Read only. The file must exist.
w - Create an empty file for writing.
a - Append to a file.The file is created if it does not exist.
r+ - Open a file for update both reading and writing. The file must exist.
w+ - Create an empty file for both reading and writing.
a+ - Open a file for reading and appending. The file is created if it does not exist.
In your case, w is preferable.
For those of us that learn by example...
Write text to a file like this:
IO.write('/tmp/msg.txt', 'hi')
BONUS INFO ...
Read it back like this
IO.read('/tmp/msg.txt')
Frequently, I want to read a file into my clipboard ***
Clipboard.copy IO.read('/tmp/msg.txt')
And other times, I want to write what's in my clipboard to a file ***
IO.write('/tmp/msg.txt', Clipboard.paste)
*** Assumes you have the clipboard gem installed
See: https://rubygems.org/gems/clipboard
To destroy the previous contents of the file, then write a new string to the file:
open('myfile.txt', 'w') { |f| f << "some text or data structures..." }
To append to a file without overwriting its old contents:
open('myfile.txt', "a") { |f| f << 'I am appended string' }
Related
So what I am trying to do is pass a file name into a method and and check if the file is closed. What I am struggling to do is getting a file object from the file name without actually opening the file.
def file_is_closed(file_name)
file = # The method I am looking for
file.closed?
end
I have to fill in the commented part. I tried using the load_file method from the YAML module but I think that gives the content of the file instead of the actual file.
I couldn't find a method in the File module to call. Is there a method maybe that I don't know?
File#closed? returns whether that particular File object is closed, so there is no method that is going to make your current attempted solution work:
f1 = File.new("test.file")
f2 = File.new("test.file")
f1.close
f1.closed? # => true # Even though f2 still has the same file open
It would be best to retain the File object that you're using in order to ask it if it is closed, if possible.
If you really want to know if your current Ruby process has any File objects open for a particular path, something like this feels hack-ish but should mostly work:
def file_is_closed?(file_name)
ObjectSpace.each_object(File) do |f|
if File.absolute_path(f) == File.absolute_path(file_name) && !f.closed?
return false
end
end
true
end
I don't stand by that handling corner cases well, but it seems to work for me in general:
f1 = File.new("test.file")
f2 = File.new("test.file")
file_is_closed?("test.file") # => false
f1.close
file_is_closed?("test.file") # => false
f2.close
file_is_closed?("test.file") # => true
If you want to know if any process has the file open, I think you'll need to resort to something external like lsof.
For those cases where you no longer have access to the original file objects in Ruby (after fork + exec, for instance), a list of open file descriptors is available in /proc/pid/fd. Each file there is named for the file descriptor number, and is a symlink to the opened file, pipe, or socket:
# Returns hash in form fd => filename
def open_file_descriptors
Hash[
Dir.glob( File.join( '/proc', Process.pid.to_s, 'fd', '*' ) ).
map { |fn| [File.basename(fn).to_i, File.readlink(fn)] rescue [nil, nil] }.
delete_if { |fd, fn| fd.nil? or fd < 3 }
]
end
# Return IO object for the named file, or nil if it's not open
def io_for_path(path)
fd, fn = open_file_descriptors.find {|k,v| path === v}
fd.nil? ? nil : IO.for_fd(fd)
end
# close an open file
file = io_for_path('/my/open/file')
file.close unless file.nil?
The open_file_descriptors method parses the fd directory and returns a hash like {3 => '/my/open/file'}. It is then a simple matter to get the file descriptor number for the desired file, and have Ruby produce an IO object for it with for_fd.
This assumes you are on Linux, of course.
post '/upload' do
unless params[:file] && (tmpfile = params[:file][:tempfile]) && (name = params[:file][:filename])
return haml(:upload)
end
time = Time.now.to_s
time.gsub!(/\s/, '')
name = time + name
while blk = tmpfile.read(65536)
File.open(File.join(Dir.pwd,"public/uploads", name), "wb") { |f| f.write(tmpfile.read) }
end
'success'
end
Everything goes where expected the files just end up being corrupted.
This bit looks really funky:
while blk = tmpfile.read(65536)
File.open(File.join(Dir.pwd,"public/uploads", name), "wb") { |f| f.write(tmpfile.read) }
end
I'm guessing you're trying to read your tempfile a 65536-byte block at a time, and then write those blocks successively to your destination file. But you never write blk, which is the first block you read; you write the rest of the file (tempfile.read) instead. And even if this loop did write blocks like it should, it opens the file anew for each block, overwriting the old contents! Anyway, I suspect you meant something like this:
File.open(File.join(Dir.pwd,"public/uploads", name), "wb") do |f|
while(blk = tempfile.read(65536))
f.write(blk)
end
end
That said, if you've got the file as a temp file (presumably already on your local file system), maybe all you need to do is move that file? It'll go way faster if that's the case - if the source and destination are on the same disk, it's just a matter of swapping some file system pointers, rather than copying all that data.
Hope that helps!
The code opens and replaces the file during every iteration of the loop, which causes part of the problem. The code also reads the tmpfile into blk then throws that data away. Time.now.to_s contains colons, which is the path separator on Mac OS X, and could cause a problem on OS X. The user-supplied filename could contain some bad stuff like .. which may allow users to overwrite files. Try this instead:
require 'pathname'
require 'zaru'
post '/upload' do
unless tmpfile = params[:file].try(:[], :tempfile)
return haml(:upload)
end
name = Zaru.sanitize!("#{Time.now.to_i}#{params[:file][:filename]}")
Pathname.pwd.join("public/uploads", name).open("wb") do |f|
while blk = tmpfile.read(65536)
f.write(blk)
end
end
'success'
end
You should also make sure that the filename doesn't end in something nefarious, like .js or .css, which could be exploited.
I want to copy the contents of one file to another using Ruby's file methods.
How can I do it using a simple Ruby program using file methods?
There is a very handy method for this - the IO#copy_stream method - see the output of ri copy_stream
Example usage:
File.open('src.txt') do |f|
f.puts 'Some text'
end
IO.copy_stream('src.txt', 'dest.txt')
For those that are interested, here's a variation of the IO#copy_stream, File#open + block answer(s) (written against ruby 2.2.x, 3 years too late).
copy = Tempfile.new
File.open(file, 'rb') do |input_stream|
File.open(copy, 'wb') do |output_stream|
IO.copy_stream(input_stream, output_stream)
end
end
As a precaution I would recommend using buffer unless you can guarantee whole file always fits into memory:
File.open("source", "rb") do |input|
File.open("target", "wb") do |output|
while buff = input.read(4096)
output.write(buff)
end
end
end
Here my implementation
class File
def self.copy(source, target)
File.open(source, 'rb') do |infile|
File.open(target, 'wb') do |outfile2|
while buffer = infile.read(4096)
outfile2 << buffer
end
end
end
end
end
Usage:
File.copy sourcepath, targetpath
Here is a simple way of doing that using ruby file operation methods :
source_file, destination_file = ARGV
script = $0
input = File.open(source_file)
data_to_copy = input.read() # gather the data using read() method
puts "The source file is #{data_to_copy.length} bytes long"
output = File.open(destination_file, 'w')
output.write(data_to_copy) # write up the data using write() method
puts "File has been copied"
output.close()
input.close()
You can also use File.exists? to check if the file exists or not. This would return a boolean true if it does!!
Here's a fast and concise way to do it.
# Open first file, read it, store it, then close it
input = File.open(ARGV[0]) {|f| f.read() }
# Open second file, write to it, then close it
output = File.open(ARGV[1], 'w') {|f| f.write(input) }
An example for running this would be.
$ ruby this_script.rb from_file.txt to_file.txt
This runs this_script.rb and takes in two arguments through the command-line. The first one in our case is from_file.txt (text being copied from) and the second argument second_file.txt (text being copied to).
You can also use File.binread and File.binwrite if you wish to hold onto the file contents for a bit. (Other answers use an instant copy_stream instead.)
If the contents are other than plain text files, such as images, using basic File.read and File.write won't work.
temp_image = Tempfile.new('image.jpg')
actual_img = IO.binread('image.jpg')
IO.binwrite(temp_image, actual_img)
Source: binread,
binwrite.
The following code is a line in an xml file:
<appId>455360226</appId>
How can I replace the number between the 2 tags with another number using ruby?
There is no possibility to modify a file content in one step (at least none I know, when the file size would change).
You have to read the file and store the modified text in another file.
replace="100"
infile = "xmlfile_in"
outfile = "xmlfile_out"
File.open(outfile, 'w') do |out|
out << File.open(infile).read.gsub(/<appId>\d+<\/appId>/, "<appId>#{replace}</appId>")
end
Or you read the file content to memory and afterwords you overwrite the file with the modified content:
replace="100"
filename = "xmlfile_in"
outdata = File.read(filename).gsub(/<appId>\d+<\/appId>/, "<appId>#{replace}</appId>")
File.open(filename, 'w') do |out|
out << outdata
end
(Hope it works, the code is not tested)
You can do it in one line like this:
IO.write(filepath, File.open(filepath) {|f| f.read.gsub(//<appId>\d+<\/appId>/, "<appId>42</appId>"/)})
IO.write truncates the given file by default, so if you read the text first, perform the regex String.gsub and return the resulting string using File.open in block mode, it will replace the file's content in one fell swoop.
I like the way this reads, but it can be written in multiple lines too of course:
IO.write(filepath, File.open(filepath) do |f|
f.read.gsub(//<appId>\d+<\/appId>/, "<appId>42</appId>"/)
end
)
replace="100"
File.open("xmlfile").each do |line|
if line[/<appId>/ ]
line.sub!(/<appId>\d+<\/appId>/, "<appId>#{replace}</appId>")
end
puts line
end
The right way is to use an XML parsing tool, and example of which is XmlSimple.
You did tag your question with regex. If you really must do it with a regex then
s = "Blah blah <appId>455360226</appId> blah"
s.sub(/<appId>\d+<\/appId>/, "<appId>42</appId>")
is an illustration of the kind of thing you can do but shouldn't.
I have this little program I write in ruby. I found a nice piece of code here, on SO, to find and replace something in a file, but it doesn't seems to work.
Here's the code:
#!/usr/bin/env ruby
DOC = "test.txt"
FIND = /,,^M/
SEP = "\n"
#make substitution
File.read(DOC).gsub(FIND, SEP)
#Check if the line already exist
unique_lines = File.readlines(DOC).uniq
#Save the result in a new file
File.open('test2.txt', 'w') { |f| f.puts(unique_lines) }
Thanks everybody !
I skip the check you make to see if the line already exists and usually go with something like this (here I want to replace 'FOO' with 'BAR'):
full_path_to_read = File.expand_path('~/test1.txt')
full_path_to_write = File.expand_path('~/test2.txt')
File.open(full_path_to_read) do |source_file|
contents = source_file.read
contents.gsub!(/FOO/, 'BAR')
File.open(full_path_to_write, "w+") { |f| f.write(contents) }
end
The use of expand_path is also probably a bit pedantic here, but I like it just so that I don't accidentally clobber some file I didn't mean to.