Strange difference between irb and ruby

Ruby
1

Hello,
I’m a just beginner to ruby and impressed by the possibility to test
code in irb. Today I wrote a line of code in irb and it behaved as I
expected. But when I inserted it in my program and executed with ruby,
the code-block didn’t worke. Maybe you could tell me why.

The line

a.scan(reg_exp).each {|w| print "#{w.to_s}: "; a.sub!(reg_exp,
gets.chomp)}

It asked me in irb depending on the size of ‘a’ for some input and
replaced a part (I used the Regular Expression /<\w*>/) of the string
‘a’ with my input.
But if I use this line in a program, the part ‘gets.chomp’ seems to be
ignored. The result is no change on String ‘a’.

I’ve no explanation for this strange behaviour, I hope you can give me
a hint. Maybe the whole line is rubbish and there is a lot better way
to do the job?

Thanks,
naPOLeon

2

naPOLeon wrote:

Hello,
I’m a just beginner to ruby and impressed by the possibility to test
code in irb. Today I wrote a line of code in irb and it behaved as I
expected. But when I inserted it in my program and executed with ruby,
the code-block didn’t worke. Maybe you could tell me why.

The line

a.scan(reg_exp).each {|w| print "#{w.to_s}: "

w is already a string.

        ; a.sub!(reg_exp,

gets.chomp)}

To me, it doesn’t make sense to change the string
while you are scanning it.

Try this:

a = "foo bar "
reg_exp = /<\w*>/
a.gsub!(reg_exp) { |w| print "#{w}: "; gets.chomp }

p a

3

On Sunday 30 July 2006 21:05, naPOLeon wrote:

gets.chomp)}

It asked me in irb depending on the size of ‘a’ for some input and
replaced a part (I used the Regular Expression /<\w*>/) of the
string ‘a’ with my input.
But if I use this line in a program, the part ‘gets.chomp’ seems to
be ignored. The result is no change on String ‘a’.

I don’t know if this is the problem here, but:
“gets” might not do exactly what you think it does…
Try changing it to “$stdin.gets”.

Read:
$ ri Kernel#gets
That’s what you use now…
and:
$ ri IO#gets
That’s what you call with $stdin.gets.

HTH,
Stefan

4

Thanks William and Stefan,

your right, gsub! is a better way to do what I want. But your solution
doesn’t work, either. I think ruby has a problem by invoking gets.chomp
(by the way Stefan, it made for me no difference to use $stdin.gets
instead of gets )-: in a block. I hope you know a workaround (I tried
to write …do…end instead of {}, but it doesn’t changed anything in
the behaviour of my program)

thanks,
naPOLeon