ARGV, STDIN and gets

ruby-talk
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 (http://www.ruby-doc.org/core/classes/Kernel.html#M005996). 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

···

--
Name: Joseph A. Williams
Email: joe@joetify.com
Blog: http://www.joeandmotorboat.com/

2

Hi,

At Sat, 25 Apr 2009 07:43:28 +0900,
Joe Williams 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.

···

--
Nobu Nakada

3

Joe Williams wrote:

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

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"]

···

--
       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407

4

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

Thanks!

-Joe

Joel VanderWerf wrote:

···

Joe Williams wrote:

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

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"]

--
Name: Joseph A. Williams
Email: joe@joetify.com
Blog: http://www.joeandmotorboat.com/

5

Nobuyoshi Nakada wrote:

Hi,

At Sat, 25 Apr 2009 07:43:28 +0900,
Joe Williams 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!

···

--
Posted via http://www.ruby-forum.com/\.

6

Prakash Murthy wrote in post #929972:

Nobuyoshi Nakada wrote:

Hi,

At Sat, 25 Apr 2009 07:43:28 +0900,
Joe Williams 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.

···

--
Posted via http://www.ruby-forum.com/\.

7

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

···

On Wed, May 25, 2011 at 7:05 AM, Daniel C. <daniel_antonio_n@yahoo.com> wrote:

Prakash Murthy wrote in post #929972:

Nobuyoshi Nakada wrote:

Hi,

At Sat, 25 Apr 2009 07:43:28 +0900,
Joe Williams 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.

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/