Help with customising the IRB prompt

Ruby
1

Hi, I’m new to this newsgroup, so I’m not sure if this is the right
place to ask.

Ok, so what I’m trying to do is customise the IRB prompt in a rather
complicated way: I want to print %i*2 (or even just %i) spaces at the
beginning of each line of prompt. Here was my best attempt (not sure
if there’s a better way to format this for Usenet):

IRB.conf[:PROMPT][:INDENTS] = {
:PROMPT_I => "#{%i.times {print ’ '}} >> ",
:PROMPT_S => "#{%i.times {print ’ '}} >> ",
:PROMPT_C => "#{%i.times {print ’ '}} >> ",
:RETURN => “=> %s\n”
}

So, what I want it do is like this:

if “Jim” == “Fred”
print “Ruby Sucks!”
else
print “Ruby is cool!”
end
print “And you know it!”

But obviously, It tries to work out the value of the #{ } as soon as
it’s set, not when it’s displayed, after the %i has been gsub’d for
displaying. So, I get an error thrown at me.

Does anybody know how to do this? Maybe some printf() trickery?

Thanks in advance.

2

This is a constant so you cannot just assign it a dynamic value.

If you really want, you can assign it an instance of a class that
exposes an interface similar to that of a Hash but acts dynamically.

You’d still need to somehow get the value of “%i”, whatever that is
(I’m not familiar with IRB configuration but I know it’s very hard to
achieve this with Ruby so I just guess you meant @i or something (if
I’m wrong, sorry)).

You might as well just modify a few lines of IRB code, I guess.

By the way, printf() like formatitng in Ruby has a great syntax:

“%f” % 0.1
“%d %d” % [1, 2]

(String could be dynamic, Numerics could be dynamic, Array could be
dynamic).

Have a look at the Adopt-a-newbie thread here in the mailing list :slight_smile:

Aur S.

3

I was a bit unclear, so let me give an example:

class Hashlike < Hash
def [] (key)
return " " * $indentation_level if key == :PROMPT_I
super
end
end

IRB.conf[:PROMPT][:INDENTS] = Hashlike.new( # can I pass a Hash to
Hash.new ?
:PROMPT_I => "#{%i.times {print ’ '}} >> ",
:PROMPT_S => "#{%i.times {print ’ '}} >> ",
:PROMPT_C => "#{%i.times {print ’ '}} >> ",
:RETURN => “=> %s\n”

You might be able to achieve a similar effect with a Hash and a
default block, I don’t remember it’s syntax.

Aur S.

4

IRB.conf[:AUTO_INDENT]=true

It’s not actually what you want, but it’s pretty good.

–
Giles B.
http://www.gilesgoatboy.org

http://gilesgoatboy.blogspot.com