Clash Royale CLAN TAG#URR8PPP

How to create a text file in Ruby owned by root?

It's trivially easy in Ruby to create a text file as the current user using File.write, but if I want the file to be owned by root, it becomes a lot more complicated.

File.write

I realize that I could run the Ruby script itself with sudo but would prefer not to do that.

sudo

How can I do this?

chown root <filename>

sudo chown root <filename>

sudoers

sudo

root

sudo

1 Answer
1

Rather than trying to create or open the file as root (which I believe is impossible if the Ruby script has been started as a nonroot user), the file can be created as the current user first and then have its ownership and permissions changed.

As a practical matter it probably makes sense to use Ruby's Tempfile functionality to create the initial file, since it eliminates the need to determine a unique filename and will not require that the current directory be writable. Here is the code I came up with (it's also posted at https://gist.github.com/keithrbennett/2c6f53351bf9cdb0bbbfd3f7f97dc91c). The module is defined and the call to it is on the last line. I've made some assumptions, e.g. that the file should be world readable:

Tempfile

#!/usr/bin/env ruby

require 'tempfile'

module SudoFileWriter

module_function

# Writes passed text to a temp file.
# @return the filespec of the temp file.
def write_to_temp_file(text)
filespec = nil
Tempfile.open do |file|
file.write(text)
filespec = file.path
end
filespec
end


def write_to_root_file(filespec, text)
temp_filespec = write_to_temp_file(text)
commands = [
"sudo chown root:wheel #temp_filespec",
"sudo mv #temp_filespec #filespec",
"sudo chmod +r #filespec"
]
puts "Running commands for file #filespec:nn"; puts commands
`#commands.join(' && ')`
end


def call(filespec, object_to_write)
write_to_root_file(filespec, object_to_write.to_s)
end
end

# .() is shorthand for .call().
# `module_function` above results in all methods being both module level
# and instance level methods, so we can call directly on the module object.

SudoFileWriter.('root-owned-file.txt', "The time is now #Time.now.n")


Output looks like this:

Running commands for file root-owned-file.txt:

sudo chown root:wheel /var/folders/bk/8y3jvjs53qs9wlqtpzqq6_080000gn/T/20180810-9981-124bxcl
sudo mv /var/folders/bk/8y3jvjs53qs9wlqtpzqq6_080000gn/T/20180810-9981-124bxcl root-owned-file.txt
sudo chmod +r root-owned-file.txt
Password:
The time is now 2018-08-10 16:01:05 +0700.


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