How to find text file in same directory

Question

I am trying to read a list of baby names from the year 1880 in CSV format. My program, when run in the terminal on OS X returns an error indicating yob1880.txt doesnt exist.

No such file or directory @ rb_sysopen - /names/yob1880.txt   (Errno::ENOENT)
from names.rb:2:in `<main>'

The location of both the script and the text file is /Users/*****/names.

lines = []

File.expand_path('../yob1880.txt', __FILE__)
IO.foreach('../yob1880.txt') do |line|
  lines << line
  if lines.size >= 1000
    lines = FasterCSV.parse(lines.join) rescue next
    store lines
    lines = []
  end
end
store lines

Answer 1

If you're running the script from the /Users/*****/names directory, and the files also exist there, you should simply remove the "../" from your pathnames to prevent looking in /Users/***** for the files.

Use this approach to referencing your files, instead:

File.expand_path('yob1880.txt', __FILE__)
IO.foreach('yob1880.txt') do |line|

Note that the File.expand_path is doing nothing at the moment, as the return value is not captured or used for any purpose; it simply consumes resources when it executes. Depending on your actual intent, it could realistically be removed.

Going deeper on this topic, it may be better for the script to be explicit about which directory in which it locates files. Consider these approaches:

Change to the directory in which the script exists, prior to opening files

Dir.chdir(File.dirname(File.expand_path(__FILE__)))
IO.foreach('yob1880.txt') do |line|

This explicitly requires that the script and the data be stored relative to one another; in this case, they would be stored in the same directory.

Provide a specific path to the files

# do not use Dir.chdir or File.expand_path
IO.foreach('/Users/****/yob1880.txt') do |line|

This can work if the script is used in a small, contained environment, such as your own machine, but will be brittle if it data is moved to another directory or to another machine. Generally, this approach is not useful, except for short-lived scripts for personal use.

Never put a script using this approach into production use.

Work only with files in the current directory

# do not use Dir.chdir or File.expand_path
IO.foreach('yob1880.txt') do |line|

This will work if you run the script from the directory in which the data exists, but will fail if run from another directory. This approach typically works better when the script detects the contents of the directory, rather than requiring certain files to already exist there.

Many Linux/Unix utilities, such as cat and grep use this approach, if the command-line options do not override such behavior.

Accept a command-line option to find data files

require 'optparse'

base_directory = "."

OptionParser.new do |opts|
  opts.banner = "Usage: example.rb [options]"

  opts.on('-d', '--dir NAME', 'Directory name') {|v| base_directory = Dir.chdir(File.dirname(File.expand_path(v))) }
end

IO.foreach(File.join(base_directory, 'yob1880.txt')) do |line|
  # do lines
end

This will give your script a -d or --dir option in which to specify the directory in which to find files.

Use a configuration file to find data files

This code would allow you to use a YAML configuration file to define where the files are located:

require 'yaml'

config_filename = File.expand_path("~/yob/config.yml")
config = {}
name = nil

config = YAML.load_file(config_filename)
base_directory = config["base"]

IO.foreach(File.join(base_directory, 'yob1880.txt')) do |line|
  # do lines
end

This doesn't include any error handling related to finding and loading the config file, but it gets the point across. For additional information on using a YAML config file with error handling, see my answer on Asking user for information, and never having to ask again.

Final thoughts

You have the tools to establish ways to locate your data files. You can even mix-and-match solutions for a more sophisticated solution. For instance, you could default to the current directory (or the script directory) when no config file exists, and allow the command-line option to manually override the directory, when necessary.

Answer 2

Here's a technique I always use when I want to normalize the current working directory for my scripts. This is a good idea because in most cases you code your script and place the supporting files in the same folder, or in a sub-folder of the main script.

This resets the current working directory to the same folder as where the script is situated in. After that it's much easier to figure out the paths to everything:

# Reset working directory to same folder as current script file
Dir.chdir(File.dirname(File.expand_path(__FILE__)))

After that you can open your data file with just:

IO.foreach('yob1880.txt')