Question

I have a file with one or more key:value lines, and I want to pull a key:value out if key=foo. How can I do this?

I can get as far as this:

if File.exist?('/file_name')
  content = open('/file_name').grep(/foo:??/)

I am unsure about the grep portion, and also once I get the content, how do I extract the value?

Answer 1

People like to slurp the files into memory, which, if the file will always be small, is a reasonable solution. However, slurping isn’t scalable, and the practice can lead to excessive CPU and I/O waits as content is read.

Instead, because you could have multiple hits in a file, and you’re comparing the content line-by-line, read it line-by-line. Line I/O is very fast and avoids the scalability problems. Ruby’s File.foreach is the way to go:

File.foreach('path/to/file') do |li|
  puts $1 if li[/foo:\s*(\w+)/]
end

Because there are no samples of actual key/value pairs, we’re shooting in the dark for valid regex patterns, but this is the basis for how I’d solve the problem.