Asp Forum - translate Perl diamond operator to Ruby

Chad Perrin

4/15/2007 6:07:00 PM

Over the years, I've found the following to be an excellent way to whip
up quick, very useful Perl scripts:

#!/usr/bin/perl

while(<>) {
# do stuff . . .
}

Is there an equivalent idiom in Ruby? So far as I'm aware, there's no
catch-all diamond operator in Ruby that allows one to create a default
input behavior for a script that accepts either a filename or piped
output of another command the way this works in Perl. I certainly hope
there's an equivalent, though.

--
CCD CopyWrite Chad Perrin [ http://ccd.ap... ]
"The ability to quote is a serviceable
substitute for wit." - W. Somerset Maugham

11 Answers

Ken Bloom

4/15/2007 6:38:00 PM

On Mon, 16 Apr 2007 03:06:58 +0900, Chad Perrin wrote:

> Over the years, I've found the following to be an excellent way to whip
> up quick, very useful Perl scripts:
>
> #!/usr/bin/perl
>
> while(<>) {
> # do stuff . . .
> }
>
> Is there an equivalent idiom in Ruby? So far as I'm aware, there's no
> catch-all diamond operator in Ruby that allows one to create a default
> input behavior for a script that accepts either a filename or piped
> output of another command the way this works in Perl. I certainly hope
> there's an equivalent, though.

ARGF.each do |line|
# do stuff
end

--
Ken Bloom. PhD candidate. Linguistic Cognition Laboratory.
Department of Computer Science. Illinois Institute of Technology.
http://www.iit.edu...

Brian Candler

4/15/2007 8:26:00 PM

On Mon, Apr 16, 2007 at 03:06:58AM +0900, Chad Perrin wrote:
> Over the years, I've found the following to be an excellent way to whip
> up quick, very useful Perl scripts:
>
> #!/usr/bin/perl
>
> while(<>) {
> # do stuff . . .
> }
>
> Is there an equivalent idiom in Ruby? So far as I'm aware, there's no
> catch-all diamond operator in Ruby that allows one to create a default
> input behavior for a script that accepts either a filename or piped
> output of another command the way this works in Perl. I certainly hope
> there's an equivalent, though.

while gets
# do stuff with $_
end

Or, less perly,

while line = gets
# do stuff with line
end

Or, if there are multiple files listed on ARGV, and you want to slurp them
all one at a time,

while contents = gets(nil)
# do stuff with contents
end

Doing that in Perl seems quite hard.

B.

benjohn

4/15/2007 8:27:00 PM

On 15 Apr 2007, at 19:40, Ken Bloom wrote:

> On Mon, 16 Apr 2007 03:06:58 +0900, Chad Perrin wrote:
>
>> Over the years, I've found the following to be an excellent way to
>> whip
>> up quick, very useful Perl scripts:
>>
>> #!/usr/bin/perl
>>
>> while(<>) {
>> # do stuff . . .
>> }
>>
>> Is there an equivalent idiom in Ruby? So far as I'm aware,
>> there's no
>> catch-all diamond operator in Ruby that allows one to create a
>> default
>> input behavior for a script that accepts either a filename or piped
>> output of another command the way this works in Perl. I certainly
>> hope
>> there's an equivalent, though.
>
> ARGF.each do |line|
> # do stuff
> end

What _is_ ARGF? I've printed it's class, but apparently it is:

> irb(main):003:0> ARGF.class
> => Object

... an Object.

Chad Perrin

4/15/2007 10:08:00 PM

On Mon, Apr 16, 2007 at 05:27:24AM +0900, Benjohn Barnes wrote:
>
> What _is_ ARGF? I've printed it's class, but apparently it is:
>
> >irb(main):003:0> ARGF.class
> >=> Object
>
> ... an Object.
>

Now that I know ARGF exists . . .

http://www.danvk.org/wp... reports the following:

ARGF is a great crutch for Perl programmers who miss typing while(<>)
{...}. It opens each input file left in ARGV and yields each line. If
there´s no input files left, it reads STDIN and yields each line it
gets there. Many, many programs do their work in an ARGF loop.

--
CCD CopyWrite Chad Perrin [ http://ccd.ap... ]
McCloctnick the Lucid: "The first rule of magic is simple. Don't waste
your time waving your hands and hopping when a rock or a club will do."

Chad Perrin

4/15/2007 10:09:00 PM

On Mon, Apr 16, 2007 at 03:40:17AM +0900, Ken Bloom wrote:
> On Mon, 16 Apr 2007 03:06:58 +0900, Chad Perrin wrote:
>
> > Over the years, I've found the following to be an excellent way to whip
> > up quick, very useful Perl scripts:
> >
> > #!/usr/bin/perl
> >
> > while(<>) {
> > # do stuff . . .
> > }
> >
> > Is there an equivalent idiom in Ruby? So far as I'm aware, there's no
> > catch-all diamond operator in Ruby that allows one to create a default
> > input behavior for a script that accepts either a filename or piped
> > output of another command the way this works in Perl. I certainly hope
> > there's an equivalent, though.
>
> ARGF.each do |line|
> # do stuff
> end

Thanks muchly. Armed with this seed of knowledge (to mix a metaphor), I
can find the rest via Google easily. I appreciate it.

--
CCD CopyWrite Chad Perrin [ http://ccd.ap... ]
"A script is what you give the actors. A program
is what you give the audience." - Larry Wall

Chad Perrin

4/15/2007 10:23:00 PM

On Mon, Apr 16, 2007 at 05:25:41AM +0900, Brian Candler wrote:
>
> while contents = gets(nil)
> # do stuff with contents
> end
>
> Doing that in Perl seems quite hard.

Thanks for the information. As for this last example, the functionality
you achieved isn't exactly "hard" in Perl, but it's a touch less
intuitive. Slurping a file via the diamond operator should end up
looking something like this, generally:

my $foo;
{ local $/; $foo = <>; }

The "my $foo" part, for those not familiar with Perl, is just the way
the $foo variable can be declared with lexical scope. If you're writing
code without strict and warnings pragmas (indispensable debugging aids
in Perl), you could dispense with the "my $foo" line altogether.

In fact, you could dispense with the braces and use "undef $/" instead
of "local $/" if you prefer, as long as you don't care about getting the
original value of $/ back (or want to put it back in manually for some
reason).

TIMTOWTDI.

--
CCD CopyWrite Chad Perrin [ http://ccd.ap... ]
print substr("Just another Perl hacker", 0, -2);

James Gray

4/16/2007 3:15:00 AM

On Apr 15, 2007, at 3:25 PM, Brian Candler wrote:

> Or, less perly,
>
> while line = gets
> # do stuff with line
> end

I really feel the Ruby version is to use a standard iterator:

ARGF.each do |line|
# do stuff with line
end

> Or, if there are multiple files listed on ARGV, and you want to
> slurp them
> all one at a time,
>
> while contents = gets(nil)
> # do stuff with contents
> end

contents = ARGF.read

James Edward Gray II

James Gray

4/16/2007 3:18:00 AM

On Apr 15, 2007, at 5:07 PM, Chad Perrin wrote:

> On Mon, Apr 16, 2007 at 05:27:24AM +0900, Benjohn Barnes wrote:
>>
>> What _is_ ARGF? I've printed it's class, but apparently it is:
>>
>>> irb(main):003:0> ARGF.class
>>> => Object
>>
>> ... an Object.
>>
>
> Now that I know ARGF exists . . .
>
> http://www.danvk.org/wp... reports the following:
>
> ARGF is a great crutch for Perl programmers who miss typing while
> (<>)
> {...}. It opens each input file left in ARGV and yields each
> line. If
> there´s no input files left, it reads STDIN and yields each line it
> gets there. Many, many programs do their work in an ARGF loop.

I don't much care for that description. ARGF simplifies the
implementation of some very common behavior for command-line
programs. I don't feel it exists merely as a crutch for Perl
programmers.

James Edward Gray II

Chad Perrin

4/16/2007 4:17:00 AM

On Mon, Apr 16, 2007 at 12:18:12PM +0900, James Edward Gray II wrote:
> On Apr 15, 2007, at 5:07 PM, Chad Perrin wrote:
>
> >On Mon, Apr 16, 2007 at 05:27:24AM +0900, Benjohn Barnes wrote:
> >>
> >>What _is_ ARGF? I've printed it's class, but apparently it is:
> >>
> >>>irb(main):003:0> ARGF.class
> >>>=> Object
> >>
> >>... an Object.
> >>
> >
> >Now that I know ARGF exists . . .
> >
> >http://www.danvk.org/wp... reports the following:
> >
> > ARGF is a great crutch for Perl programmers who miss typing while
> >(<>)
> > {...}. It opens each input file left in ARGV and yields each
> >line. If
> > there?s no input files left, it reads STDIN and yields each line it
> > gets there. Many, many programs do their work in an ARGF loop.
>
> I don't much care for that description. ARGF simplifies the
> implementation of some very common behavior for command-line
> programs. I don't feel it exists merely as a crutch for Perl
> programmers.

Nor do I. I found the more implementation-related description to be
somewhat useful, however, once I got past the opining.

--
CCD CopyWrite Chad Perrin [ http://ccd.ap... ]
"It's just incredible that a trillion-synapse computer could actually
spend Saturday afternoon watching a football game." - Marvin Minsky

Robert Klemme

4/16/2007 11:05:00 AM

On 16.04.2007 00:08, Chad Perrin wrote:
> On Mon, Apr 16, 2007 at 03:40:17AM +0900, Ken Bloom wrote:
>> On Mon, 16 Apr 2007 03:06:58 +0900, Chad Perrin wrote:
>>
>>> Over the years, I've found the following to be an excellent way to whip
>>> up quick, very useful Perl scripts:
>>>
>>> #!/usr/bin/perl
>>>
>>> while(<>) {
>>> # do stuff . . .
>>> }
>>>
>>> Is there an equivalent idiom in Ruby? So far as I'm aware, there's no
>>> catch-all diamond operator in Ruby that allows one to create a default
>>> input behavior for a script that accepts either a filename or piped
>>> output of another command the way this works in Perl. I certainly hope
>>> there's an equivalent, though.
>> ARGF.each do |line|
>> # do stuff
>> end
>
> Thanks muchly. Armed with this seed of knowledge (to mix a metaphor), I
> can find the rest via Google easily. I appreciate it.

You can also use one of the command line switches -n or -p, e.g.

13:04:42 [tmp]: ls -l | ruby -ne 'puts "<#{$_[0,3]}>"'
<tot>
<-rw>
<lrw>
13:04:59 [tmp]:

Kind regards

robert

comp.lang.ruby

translate Perl diamond operator to Ruby

Chad Perrin

Ken Bloom

Brian Candler

benjohn

Chad Perrin

Chad Perrin

Chad Perrin

James Gray

James Gray

Chad Perrin

Robert Klemme

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