I’m running into a problem doing a conditional range in ruby. The sample
code is:
#!/usr/bin/ruby
## one
## two
## three
## four
## five
File.open($0, 'r') { |f|
while f.gets
print $_.sub(/^##/, ‘’) if /^## two/ … /^## four/
end
}
I’m expecting:
two
three
four
but I get the whole file with the leading pound signs stripped off.
What’s wrong here?
Hi,
At Mon, 4 Jun 2007 15:56:31 +0900,
Todd A. Jacobs wrote in [ruby-talk:254228]:
print $_.sub(/^##/, '') if /^## two/ .. /^## four/
print $_.sub(/^##/, '') if ~/^## two/ .. ~/^## four/
but I get the whole file with the leading pound signs stripped off.
What’s wrong here?
Because Range object isn’t nil nor false, and you’d see a
warning if you run with -w option.
warning: range literal in condition
Hi,
Implicit match against “$_” is not anymore supported in version 1.8.
You cas still use it in command line form (with “-e” option).
In regular file, you have to write the match explicitly :
one
two
three
four
five
File.open($0, ‘r’) { |f|
while f.gets
print $.sub(/^##/, ‘’) if ($ =~ /^## two/) … ($_ =~ /^## four/)
end
}
On 4 juin, 08:56, “Todd A. Jacobs” [email protected]
On Jun 4, 9:51 pm, “Todd A. Jacobs” <tjacobs-
[email protected]> wrote:
On Mon, Jun 04, 2007 at 04:35:25PM +0900, come wrote:
prints up to “four” when (as I understand it) it should stop at “three”
since “## four” would make the if-statement false. Am I still missing
something obvious?
Yes. That will never work, as this is not Perl nor are you creating a
range of regexp (which cannot be done, btw).
See what happens when the match does happen as you want:
irb> a = ‘four’
irb> (a =~ /two/)…(a =~ /four/)
ArgumentError: bad value for range
[result is: (nil…‘four’) ]
Plus the uncommented # in the regex are probably making ruby assume a
comment.
This is another way of writing what you want to do:
#!/usr/bin/ruby -w
one
two
three
four
five
File.open($0) do |file|
range = [ ‘$_ =~ /^## two/’, ‘$_ !~ /^## four/’ ]
while file.gets
if eval("#{range[0]}")
print $_.sub(/^## /, ‘’);
range.shift
end
end
end
On Mon, Jun 04, 2007 at 04:35:25PM +0900, come wrote:
Implicit match against “$_” is not anymore supported in version 1.8.
Thanks. Your explanation was very helpful. It works better now, but the
range operator still catches more than it should. For example:
#!/usr/bin/ruby -w
## one
## two
## three
## four
## five
File.open($0) do |file|
while file.gets
print $.sub(/^## /, ‘’) if
($ =~ /^## two/)…($_ =~ /^## four/)
end
end
prints up to “four” when (as I understand it) it should stop at “three”
since “## four” would make the if-statement false. Am I still missing
something obvious?
Sorry. Buggy code posted. Here’s a correct implementation.
#!/usr/bin/ruby -w
one
two
three
five
six
four
five
File.open($0) do |file|
while file.gets
if $_ =~ /^## two/
loop {
print $.sub(/^## /, ‘’)
file.gets
break if not $ or $_ =~ /^## four/
}
end
end
end
Yes, because (as with Perl) there are two forms of conditional range:
“…” and “…”.
The three dots form evaluate the condition after the code. Therefore,
the “four” is printed, then the condition is evaluated to false.
The two dots form evaluates the condition before the code. So it
should works as you expect : “($_ =~ /^## two/)…($_ =~ /^## four/)”.
On 5 juin, 02:51, “Todd A. Jacobs”