How to take two input streams? [Perl]

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From: Peng Yu on 31 May 2010 23:47

diff can take two input streams in the following example (if my
interpretation is correct).

diff <(gunzip <a.gz) <(gunzip b.gz)

I'm wondering how to take two streams in a perl program.

From: Alan Curry on 1 Jun 2010 00:12

In article <d31764b8-cd92-47d0-a0af-39292fede94d(a)f13g2000vbm.googlegroups.com>,
Peng Yu <pengyu.ut(a)gmail.com> wrote:
>diff can take two input streams in the following example (if my
>interpretation is correct).

diff *requires* two input streams. With only one, it's hard to figure what it
would do.

>
>diff <(gunzip <a.gz) <(gunzip b.gz)
>
>I'm wondering how to take two streams in a perl program.

The <(cmd) syntax is handled by your shell, which substitutes a filename
which may be opened to gain access to the stream. diff doesn't know anything
abou it. diff just finds 2 filenames in argv, opens them, and reads them. You
can do the same in any language, including perl.

--
Alan Curry

From: Martijn Lievaart on 1 Jun 2010 04:24

On Mon, 31 May 2010 20:47:22 -0700, Peng Yu wrote:

> diff can take two input streams in the following example (if my
> interpretation is correct).
>
> diff <(gunzip <a.gz) <(gunzip b.gz)
>
> I'm wondering how to take two streams in a perl program.

This has nothing to do with diff or with perl, it's a function of your
shell. So it works the same for diff as for perl.

HTH,
M4

From: Peng Yu on 1 Jun 2010 05:16

From: Peng Yu on 1 Jun 2010 05:26

On Jun 1, 3:24 am, Martijn Lievaart <m...(a)rtij.nl.invlalid> wrote:
> On Mon, 31 May 2010 20:47:22 -0700, Peng Yu wrote:
> > diff can take two input streams in the following example (if my
> > interpretation is correct).
>
> > diff <(gunzip <a.gz) <(gunzip b.gz)
>
> > I'm wondering how to take two streams in a perl program.
>
> This has nothing to do with diff or with perl, it's a function of your
> shell. So it works the same for diff as for perl.

I think that I understand what you mean. <(cmd) is just like a
filename, right?

$ cat main.pl
#!/usr/bin/env perl

use warnings;

open(IN1, $ARGV[0]);
open(IN2, $ARGV[1]);

while(<IN1>) {
print
}

print "------\n";

while(<IN2>) {
print
}

$ ./main.pl <(cat main.pl) <(cat main.pl)
#!/usr/bin/env perl

use warnings;

open(IN1, $ARGV[0]);
open(IN2, $ARGV[1]);

while(<IN1>) {
print
}

print "------\n";

while(<IN2>) {
print
}

------
#!/usr/bin/env perl

use warnings;

open(IN1, $ARGV[0]);
open(IN2, $ARGV[1]);

while(<IN1>) {
print
}

print "------\n";

while(<IN2>) {
print
}

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