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comp.lang.ruby

Using ri inside irb -- error in Pickaxe?

Ian Amuhton

1/7/2006 1:01:00 AM

The chapter in the Pickaxe 2nd ed. on irb gives some code for using `ri`
from within it:

def ri(*names)
system(%{ri #(*names.map {|name| name.to_s}.join(" ")}})
end

But that throws an error here. I'm just getting started with Ruby, so I
don't quite understand yet why you have to go through all that
rigamarole just to pass a parameter to `system 'ri keyword'`, nor what
exactly the rigamarole does :), but looking at it I can see there's an
unmatched closing curly brace before the final parens. So I changed it
to:

def ri(*names)
system(%{ri #(*names.map {|name| name.to_s}.join(" ")})
end

I tried it from within irb as "ri Proc" both in Cygwin and plain
Windows. It caused the Cygwin version to core dump (!), and the Windows
version to return this:

'name' is not recognized as an internal or external command,
operable program or batch file.
=> false

So what is proper way to write that method so I can invoke `ri` from
within irb?

Also, what is the % sign for in the `system` command above?

--
da
~~


2 Answers

Sam Smoot

1/7/2006 1:41:00 AM

0

"*names.map" should be "names.map". The * before a variable name in a
method definition is basically equiv to the "params" keyword in
Microsoft languages if that helps.

%{} is basically short-form for a HEREDOC. I don't like it personally.
A slightly cleaner example (that works) might look like this:

def ri(*names)
system("ri #{names.map { |name| name.to_s }.join(' ')}")
end

Ian Amuhton

1/7/2006 2:29:00 AM

0

ssmoot@gmail.com wrote:
> "*names.map" should be "names.map".

Ah, my error in copying.

> The * before a variable name in a method definition is
> basically equiv to the "params" keyword in Microsoft
> languages if that helps.

That much I knew. But why do you have to do all this (using your
version):

system("ri #{names.map { |name| name.to_s }.join(' ')}")

instead of just

system("ri #{names}.to_s"}

?

> %{} is basically short-form for a HEREDOC.

Ah, thanks.

> I don't like it personally.
> A slightly cleaner example (that works) might look like this:
>
> def ri(*names)
> system("ri #{names.map { |name| name.to_s }.join(' ')}")
> end

Both your version, and the original one modified with the * removed from
"names" still cause Cygwin to dump core in irb:

--------------------------------------------------------------
>> ri Proc
C:\cygwin\bin\ruby.exe (3132): *** unable to remap
C:\cygwin\lib\ruby\1.8\i386-cygwin\readline.so to same address as
parent(0x370000) != 0x2760000
C:\cygwin\bin\ruby.exe (3132): *** unable to remap
C:\cygwin\lib\ruby\1.8\i386-cygwin\readline.so to same address as
parent(0x370000) != 0x2760000
19 [main] 2888 fork_parent: child 3132 died waiting for dll
loading /home/Jelks/.irbrc:4: [BUG] rb_sys_fail() - errno == 0
ruby 1.8.3 (2005-09-21) [i386-cygwin]

Aborted (core dumped)

[blackie] ~
$

--------------------------------------------------------------

I get the same error, though without the core dump if I do it as a Ruby
program.

Under plain Windows, your version above returns "false", while the
modified original still returns:

'name' is not recognized as an internal or external command,
operable program or batch file.
=> false

Perhaps I should go fire up a Linux box. If I can get it working there,
then it must be a Ruby under Cygwin and a Ruby under Windows issues.

--
da
~~