Replace properties in one file from those in another in Ruby

Question

I want to replace properties in one file from those in another. (I am new to ruby, and read about Ruby and YAML. I have a Java background)

Eg.

File 1

server_ip_address=$[ip]
value_threshold=$[threshold]
system_name=$[sys_name]

File 2

ip=192.168.1.1
threshold=10
sys_name=foo

The ruby script should replace the $ values by their real values (I do not know if $[] is the format used in ruby. Also do Files 1 and 2 have to be YAML files, or erb files?) and produce File 1 as :

server_ip_address=192.168.1.1
value_threshold=10
system_name=foo

I searched the web for this, but could not express it in the right keywords to find a solution/pointer to a solution/reference material on google. How can this be done by a ruby script?

Thanks

Is this an arbitrary template format you've invented, or is it something you've inherited? In ERB this is done with <%= ip %> as an example. In YAML you'd define variables like ip: 192.168.1.1. — tadman
– tadman, Commented Feb 20, 2013 at 7:55
As I said in my question, "I do not know if $[] is the format used in ruby. Also do Files 1 and 2 have to be YAML files, or erb files?" — Ace McCloud
– Ace McCloud, Commented Feb 20, 2013 at 8:00
They don't have to be anything, but it would be easier if file 1 was ERB and file 2 was YAML. That you didn't know if it was used in Ruby wasn't an explanation as to where this came from. — tadman
– tadman, Commented Feb 20, 2013 at 8:06

tadman · Accepted Answer · 2013-02-20 08:16:26Z

1

If you can switch the formats, this should be as easy as:

require 'yaml'

variables = YAML.load(File.open('file2.yaml'))
template = File.read('file1.conf')

puts template.gsub(/\$\[(\w+)\]/) { variables[$1] }

Your template can stay as-is, but the substitution file would look like:

ip: 192.168.1.1
threshold: 10
sys_name: foo

This makes it easy to read in using the YAML library.

edited Feb 20, 2013 at 8:16

answered Feb 20, 2013 at 8:09

tadman

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3 Comments

Ace McCloud Over a year ago

Your script before you made an edit gave the following error

/.rvm/rubies/ruby-1.9.3-p385/lib/ruby/1.9.1/erb.rb:838:in `eval': wrong argument type Array (expected Binding) (TypeError) 	from /.rvm/rubies/ruby-1.9.3-p385/lib/ruby/1.9.1/erb.rb:838:in `result' 	from abcd.rb:5:in `<main>'

Here abcd.rb is the file into which I put the ruby script

Ace McCloud Over a year ago

Can you please post the earlier (without the edit) script (after correcting it), since i'd like to use the erb format.

tadman Over a year ago

The down-side to the ERB format, and why I removed it, was due to how you need to have local variables defined. This is considerably more awkward than simply referencing a Hash. The ERB documentation shows several examples. Creating arbitrary local variables from a YAML file is a recipe for trouble later.

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