Reading the first line of a file in Ruby

Question

I want to read only the first line of a file using Ruby in the fastest, simplest, most idiomatic way possible. What's the best approach?

(Specifically: I want to read the git commit UUID out of the REVISION file in my latest Capistrano-deployed Rails directory, and then output that to my tag. This will let me see at an http-glance what version is deployed to my server. If there's an entirely different & better way to do this, please let me know.)

Answer 1

first_line = open("filename").gets

Answer 2

You can try this:

File.foreach('path_to_file').first

Answer 3

This will read exactly one line and ensure that the file is properly closed immediately after.

File.open('somefile.txt') {|f| f.readline}

Answer 4

How to read the first line in a ruby file:

commit_hash = File.open("filename.txt").first

Alternatively you could just do a git-log from inside your application:

commit_hash = `git log -1 --pretty=format:"%H"`

The %H tells the format to print the full commit hash. There are also modules which allow you to access your local git repo from inside a Rails app in a more ruby-ish manner although I have never used them.

Answer 5

I think the jkupferman suggestion of investigating the git --pretty options makes the most sense, however yet another approach would be the head command e.g.

ruby -e 'puts head -n 1 filename' #(backtick before head and after filename)