Substring within string - ruby

Question

I need to extract from an input everything that is after a parameter.
Input: "-a Apple -b Ball -c Chocolate"
Criteria: Need to extract everything after -c.
My output should be Chocolate. I tried split, scan and the output returned two elements. Can anyone help me with this requirement?
Also, request you to let me know how to handle if my input is "-a Apple -c Chocolate -b Ball".

Answer 1

You can use the OptionParser library to do this:
require 'optparse'
arguments = { }
opts = OptionParser.new do |parser|
parser.on('-a=s') do |v|
arguments[:a] = v
end
parser.on('-b=s') do |v|
arguments[:b] = v
end
parser.on('-c=s') do |v|
arguments[:c] = v
end
end
opts.parse("-a Apple -b Ball -c Chocolate".split)
arguments
# => {:a=>"Apple", :b=>"Ball", :c=>"Chocolate"}
It's quite flexible in how it works, so you can define a lot of options and how they're interpreted.

Answer 2

If you really want everything after the marker (-c):
s = "-a Apple -b Ball -c Chocolate"
index = s.index('-c')
everything_after = s[(index + 2)..-1]
puts everything_after # => Chocolate
If you want to parse the arguments:
require 'optparse'
opts = OptionParser.new do |parser|
parser.on('-a=s') do |v|
end
parser.on('-b=s') do |v|
end
parser.on('-c=s') do |v|
puts "-c is #{v}"
end
end
opts.parse("-a Apple -b Ball -c Chocolate".split(/\s/))
(you will need to specify all the flags, otherwise the parser will choke)
Or you could simply match the content with a Regexp.
I think you are looking for: <ANYTHING><FLAG><ANYTHING BUT DASH><ANYTHING> where <FLAG> is '-c '
s.match(/\A.*-c\s([^-]*).*\z/) do |match|
p match[1]
end

Answer 3

Assuming that the input is the command line arguments passed to a ruby script, try:
ARGV[ARGV.index("-c") + 1]
Explanation:
ARGV is an array that includes all the arguments passed to a ruby script. Array#index returns the index of the first object in self.
Refer to Array#index for more info.

Answer 4

s = "-a Apple -b Ball -c Chocolate"
One way: calculate an index
marker = "-c"
s[s.index(marker)+marker.size+1..-1]
#=> "Chocolate"
marker = "-b"
s[s.index(marker)+marker.size+1..-1]
#=> "Ball -c Chocolate"
marker = "-a"
s[s.index(marker)+marker.size+1..-1]
#=> "Apple -b Ball -c Chocolate"
Another way: use a regex
`\K` in the regex below means "forget everything matched so far".
marker = "-c"
s[/#{marker}\s+\K.*/]
#=> "Chocolate"
marker = "-b"
s[/#{marker}\s+\K.*/]
#=> "Ball -c Chocolate"
marker = "-a"
s[/#{marker}\s+\K.*/]
#=> "Apple -b Ball -c Chocolate"
Consider the regex for one of these markers.
marker = "-a"
r = /
#{marker} # match the contents of the variable 'marker'
\s+ # match > 0 whitespace chars
\K # forget everything matched so far
.* # match the rest of the line
/x # free-spacing regex definition mode
#=> /
# -a # match the contents of the variable 'marker'
# \s+ # match > 0 whitespace chars
# \K # forget everything matched so far
# .* # match the rest of the line
# /x
s[r]
#=> "Apple -b Ball -c Chocolate"
But if you really want just the text between markers
I will construct a hash with markers as keys and text as values. First, we will use the following regex to split the string.
r = /
\s* # match >= 0 spaces
\- # match hypen
( # begin capture group 1
[a-z] # match marker
) # end capture group 1
\s* # match >= 0 spaces
/x # free-spacing regex definition mode
h = s.split(r).drop(1).each_slice(2).to_h
#=> {"a"=>"Apple", "b"=>"Ball", "c"=>"Chocolate"}
With this hash we can retrieve the text for each marker.
h["a"]
#=> "Apple"
h["b"]
#=> "Ball"
h["c"]
#=> "Chocolate"
The steps to create the hash are as follows.
a = s.split(r)
#=> ["", "a", "Apple", "b", "Ball", "c", "Chocolate"]
Notice that, by putting [a-z] within a capture group in the regex, "a", "b" and "c" are included in the array a. (See String#split, third paragraph.)
b = a.drop(1)
#=> ["a", "Apple", "b", "Ball", "c", "Chocolate"]
c = b.each_slice(2)
#=> #<Enumerator: ["a", "Apple", "b", "Ball", "c", "Chocolate"]:each_slice(2)>
We can see the elements of the enumerator c by converting it to an array:
c.to_a
#=> [["a", "Apple"], ["b", "Ball"], ["c", "Chocolate"]]
Lastly,
c.to_h
#=> {"a"=>"Apple", "b"=>"Ball", "c"=>"Chocolate"}