ARGV, STDIN and gets

Ruby
1

I am running into an issue where I have a script that takes two command
line arguments and reads from stdin. It seems that gets is not getting
to stdin because it is hitting ARGV first
(module Kernel - RDoc Documentation). Is there a
way around this so that I can pass in arguments and listen on stdin as
well. Running the script without args works perfectly. What I am doing
currently looks something like the following:

var1 = ARGV[0]
var2 = ARGV[1]
var3 = gets

Any advice would be helpful.

Thanks.
-Joe

2

Hi,

At Sat, 25 Apr 2009 07:43:28 +0900,
Joe W. wrote in [ruby-talk:334959]:

I am running into an issue where I have a script that takes two command
line arguments and reads from stdin. It seems that gets is not getting
to stdin because it is hitting ARGV first

Kernel#gets is not a method to read from stdin.

Use $stdin.gets.

3

Joe W. wrote:

var3 = gets

Any advice would be helpful.

Thanks.
-Joe

Kernel#gets reads from ARGF, which, if there’s anything in ARGV, is read
from those files. So you can clear from ARGV first, if you want the
option of passing your file as the 3rd arg instead of stdin.

$ cat tt.rb
var1 = ARGV.shift
var2 = ARGV.shift
var3 = gets
p [var1, var2, var3]

$ cat data
this is some text
$ ruby tt.rb foo bar data
[“foo”, “bar”, “this is some text\n”]
$ ruby tt.rb foo bar
type some input
[“foo”, “bar”, “type some input\n”]

4

ARGV.shift works perfectly, should have thought of that.

Thanks!

-Joe

5

Prakash Murthy wrote in post #929972:

Nobuyoshi N. wrote:

Hi,

At Sat, 25 Apr 2009 07:43:28 +0900,
Joe W. wrote in [ruby-talk:334959]:

I am running into an issue where I have a script that takes two command
line arguments and reads from stdin. It seems that gets is not getting
to stdin because it is hitting ARGV first

Kernel#gets is not a method to read from stdin.

Use $stdin.gets.

Thanks Nobuyoshi!

I used $stdin.gets. instead of gets. and that solved the problem I was
facing!

The solution is more very easy, like this:

var2 = ARGV[1].clone
ARGV.clear
var3 = gets

its work! not need STDIN! :slight_smile: no error more.

6

Nobuyoshi N. wrote:

Hi,

At Sat, 25 Apr 2009 07:43:28 +0900,
Joe W. wrote in [ruby-talk:334959]:

I am running into an issue where I have a script that takes two command
line arguments and reads from stdin. It seems that gets is not getting
to stdin because it is hitting ARGV first

Kernel#gets is not a method to read from stdin.

Use $stdin.gets.

Thanks Nobuyoshi!

I used $stdin.gets. instead of gets. and that solved the problem I was
facing!

7

On Wed, May 25, 2011 at 7:05 AM, Daniel C. [email protected]
wrote:

Kernel#gets is not a method to read from stdin.
var2 = ARGV[1].clone
ARGV.clear
var3 = gets

its work! not need STDIN! :slight_smile: no error more.

Why do you clone when the next thing that you do is clearing ARGV?
That seems superfluous.

For one argument I would do

arg = ARGV.shift or abort “ERROR: need at least one argument”

For more arguments I’d probably do

arg1, arg2 = ARGV.slice! 0, 2
abort “Need two arguments!” unless arg2

gets # reads stdin or from file if there are more arguments

If there is a need for more complex argument processing I would use
OptionParser anyway.

OptionParser.new do |opts|
…
end.parse! ARGV # removes options

Kind regards

robert