ARGV logic (cli arguments into variables)

Ruby
1

Hi,

I am slowly learning Ruby and for now I am really confused with one
thing.

When I am trying to pass arguments from the cli, I can’t understand why:

user = ARGV.first

and

file1, file2 = ARGV

works, but

file1 = ARGV

NOT

Does that mean when using ARGV and making from arguments variables,
there have to be more than one for using the second way?

Thanks in advace…

2

ARGV is an array, you can pass more than one arguments using comamnd
line if you want to pass only one element thats not a problem.

ARGV[0] will have your first argument.

ARGV.each do|a|
puts “Argument: #{a}”
end

3

Thank you, however, this is somewhat indirect answer. I am still
confused why one solution works just with two variables. When I am using
just one, I have to use another way.

cli> ruby ex66.rb test1.txt text2.txt

script ex66.rb>

first, second = ARGV
input = File.open(first)
…
output = File.open(second, ‘w’)
…

works perfectly, the simplest

cli> ruby ex66.rb test1.txt

script ex66.rb>

input = ARGV
input = File.open(input)
…

does not. I have to explicitly say input = ARGV.first, which is exactly
what I have not to in the first case.

4

Thanks, this is much closer.

However, I still can’t figure why only:

first = ARGV

does not work :confused:

I would expect that

first, second = ARGV
and
first = ARGV

are the same way of defining variables taken from the cli.

5

Honza Hejzl wrote in post #1152806:

first, second = ARGV

there are several variable on left part of assignment, so ruby
interprete this multiple assignement

first, second = *ARGV

which is equivalent to

first, second = ARGV[0],ARGV[1]

which is equivalent to

first = ARGV[0]
second =ARGV[1]

6

Wow, this could be a sort of magic…

first = ARGV[0] > works
first, = ARGV > works too!
first = ARGV.first > works!
first = ARGV > does not work

first, second = ARGV > works
first, second = ARGV[0], ARGV[1] > works