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comp.lang.ruby

expanding environment variable

Daniel Schoch

3/3/2009 2:28:00 PM

Hi,

I have a string
s = "$DIR/test/$FILE"

Is there an easy way to expand this with the defined environment
variables?
I can always write a quick parser, but I was wondering maybe this
already exists?

Thanks
ds
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8 Answers

Daniel Schoch

3/3/2009 2:59:00 PM

0

Dominik Honnef wrote:
> On [Tue, 03.03.2009 23:28], Daniel Schoch wrote:
>> Hi,
>>
>> I have a string
>> s = "$DIR/test/$FILE"
>>
>> Is there an easy way to expand this with the defined environment
>> variables?
> What do you mean by environment variables? The stuff in ENV, or the
> constants like __FILE__ or simply global variables?

I mean the stuff in ENV.
SHELL:
export DIR=x
export FILE=y.z

RUBY:
I'd like to know the easiest way from
s = "$DIR/test/$FILE"
to
s = "x/test/y.z"


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Daniel Schoch

3/3/2009 3:16:00 PM

0

Dominik Honnef wrote:

> | >>> DIR=x FILE=y.z irb
> | >> s = "$DIR/test/$FILE".gsub(/\$\w+/) {|m| ENV[m[1..-1]]}
> | => "x/test/y.z"
>
> Thats how I would do it.

Perfect, thanks. I sometimes have a hard time with those efficient
one-liners. It's all so cryptic.
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Brian Candler

3/3/2009 3:47:00 PM

0

Dominik Honnef wrote:
> On [Tue, 03.03.2009 23:58], Daniel Schoch wrote:
>> > constants like __FILE__ or simply global variables?
>> s = "x/test/y.z"
>>
>>
> | >>> DIR=x FILE=y.z irb
> | >> s = "$DIR/test/$FILE".gsub(/\$\w+/) {|m| ENV[m[1..-1]]}
> | => "x/test/y.z"
>
> Thats how I would do it.

Or: s = "$DIR/test/$FILE".gsub(/\$(\w+)/) { ENV[$1] }
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Daniel Schoch

3/3/2009 4:25:00 PM

0

Dominik Honnef wrote:
> On [Wed, 04.03.2009 00:16], Daniel Schoch wrote:
>> Perfect, thanks. I sometimes have a hard time with those efficient
>> one-liners. It's all so cryptic.
>
> Well, the only really cryptic thing about this one is the regexp, but
> thats just a matter of learning regular expressions. And well, the
> rest are basic ruby idioms/features like blocks. Comes time comes
> knowledge, you will get used to those one-liners :)

That is true. I'm used to the old-fashioned programming of C, assembly
and such. There, things go with baby-steps, you do one little thing at a
time.
All of a sudden with perl/ruby and such you can do tons of stuff with
few lines. My brain is not wired for this. I have a hard time forming a
ruby-worthy solution around a problem, as I'm always falling back to C's
small step way of thinking. But you're right, comes time comes
knowledge.
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Gary Wright

3/3/2009 4:31:00 PM

0


On Mar 3, 2009, at 10:50 AM, Dominik Honnef wrote:
>> Or: s = "$DIR/test/$FILE".gsub(/\$(\w+)/) { ENV[$1] }
> Probably depends on whether you like global variables or not. It is
> definitely shorter/more readable and I actually didn't know if gsub
> sets $1.

$1 isn't a true global variable. It is a per-thread variable. It
still is a bit 'magic' for many people's tastes but it isn't as bad
as a true global.

Gary Wright

Robert Klemme

3/3/2009 5:30:00 PM

0

On 03.03.2009 15:58, Daniel Schoch wrote:
> Dominik Honnef wrote:
>> On [Tue, 03.03.2009 23:28], Daniel Schoch wrote:
>>> Hi,
>>>
>>> I have a string
>>> s = "$DIR/test/$FILE"
>>>
>>> Is there an easy way to expand this with the defined environment
>>> variables?
>> What do you mean by environment variables? The stuff in ENV, or the
>> constants like __FILE__ or simply global variables?
>
> I mean the stuff in ENV.
> SHELL:
> export DIR=x
> export FILE=y.z
>
> RUBY:
> I'd like to know the easiest way from
> s = "$DIR/test/$FILE"
> to
> s = "x/test/y.z"

Just wondering: is there anything that would prevent doing this:

s = "#{ENV["DIR"]/test/#{ENV["FILE"]}"

or even

s = File.join ENV["DIR"], "test", ENV["FILE"]

? In other words: is the format of your original string mandatory? If
not, I'd rather choose one of the other approaches.

Kind regards

robert

Rick DeNatale

3/3/2009 6:04:00 PM

0

[Note: parts of this message were removed to make it a legal post.]

On Tue, Mar 3, 2009 at 11:30 AM, Gary Wright <gwtmp01@mac.com> wrote:

>
> On Mar 3, 2009, at 10:50 AM, Dominik Honnef wrote:
>
>> Or: s = "$DIR/test/$FILE".gsub(/\$(\w+)/) { ENV[$1] }
>>>
>> Probably depends on whether you like global variables or not. It is
>> definitely shorter/more readable and I actually didn't know if gsub
>> sets $1.
>>
>
> $1 isn't a true global variable. It is a per-thread variable. It
> still is a bit 'magic' for many people's tastes but it isn't as bad
> as a true global.
>

Actually its really a frame local variable. heres a bit of artificial code
which illustrates this:

def m1(string)
string.scan(/(ab|ac)/) {|m|
puts "in m1 $1 is #{$1}"
result = m2($1)
puts "result is #{result}, $1 is #{$1}"
}
end

def m2(string)
"z#{string}".scan(/(za)/) {|m|
puts "in m2 $1 is #{$1}"
$1
}
end

m1("abcac") # => "abcac"
# >> in m1 $1 is ab
# >> in m2 $1 is za
# >> result is zab, $1 is ab
# >> in m1 $1 is ac
# >> in m2 $1 is za
# >> result is zac, $1 is ac


--
Rick DeNatale

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Peña, Botp

3/4/2009 2:11:00 AM

0

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