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comp.lang.ruby

using a variable as 1st param in gsub

louis

1/12/2008 11:40:00 PM

hi all,

i'm trying to use a user entered variable in a gsub method and for
some reason, if i insert it within a regex it doesn't work. passing it
as-is works fine. en example will be clearer:

#
#
user_variable = 'some_word' # retrieved from 'gets.chomp'
cleaned_variable = '^' + user_variable + '|\s' + user_variable + '(?!\w)'

# print out variable to see if concat worked:
puts cleaned_variable #=> prints out correct regex

p some-sentence-string.gsub(%r{cleaned_variable},'TEST') # => prints
out sentence unchanged

#---
# however if i pass it like this, it works:

p some-sentence-string.gsub(%r{user_variable},'TEST')
OR
p some-sentence-string.gsub(user_variable,'TEST')

#----

now the problem is if that variable exists within another word (e.g.
'he' matches 'hello', 'the', 'she', etc.), those match too. here's the
clincher: in irb it works as i expect. only when run inside a script
does it not work! that is, the exact same code, pasted in irb, runs
correctly.

is there something different about the parser? i thought irb just used
the same parser. what am i doing wrong? any tips for troubleshooting?
is this a bug? am i a bug?

thanks,

louis

p.s. i've also
1. concatenated '/' in the cleaned variable
2. tried to pass w/o %r{} using /cleaned_variable/ and /user_variable/
(i know, i didn't expect the latter to do anything different--just
trying anything)

p.p.s. using similar methods in python works fine (for whatever that's
worth). i haven't tried it in another language yet.

p. * 3 + s. sorry if this is a repost--i first used nabble but that
post didn't show up on any other mirror of the mailing-list, so i'm
posting again.
2 Answers

Phrogz

1/13/2008 4:55:00 AM

0

On Jan 12, 4:39 pm, louis <louisju...@gmail.com> wrote:
> user_variable = 'some_word' # retrieved from 'gets.chomp'
> cleaned_variable = '^' + user_variable + '|\s' + user_variable + '(?!\w)'
>
> # print out variable to see if concat worked:
> puts cleaned_variable  #=> prints out correct regex
>
> p some-sentence-string.gsub(%r{cleaned_variable},'TEST') # => prints
> out sentence unchanged

%r{foo} is the same as /foo/...you're using the name of the variable,
not the contents. You want:
/#{foo}/ or %r{#{foo}} or %r|#{foo}| or ...
or Regexp.new( foo )

louis

1/13/2008 1:19:00 PM

0

ahah! makes perfect sense. I thought interpolation in ruby using that
construct was for double quoted strings. and since it worked in irb I
was confused.
I'm not at a machine now so I can't test your suggestion but I'll
assume its correct.

thanks a lot for the help!



On 1/12/08, Phrogz <phrogz@mac.com> wrote:
> On Jan 12, 4:39 pm, louis <louisju...@gmail.com> wrote:
> > user_variable = 'some_word' # retrieved from 'gets.chomp'
> > cleaned_variable = '^' + user_variable + '|\s' + user_variable + '(?!\w)'
> >
> > # print out variable to see if concat worked:
> > puts cleaned_variable #=> prints out correct regex
> >
> > p some-sentence-string.gsub(%r{cleaned_variable},'TEST') # => prints
> > out sentence unchanged
>
> %r{foo} is the same as /foo/...you're using the name of the variable,
> not the contents. You want:
> /#{foo}/ or %r{#{foo}} or %r|#{foo}| or ...
> or Regexp.new( foo )
>
>