Prev: How to generate random number without replacement?
Next: FAQ 4.76 How do I verify a credit card checksum?
From: Peter Makholm on 1 Jun 2010 05:40
Peng Yu <pengyu.ut(a)gmail.com> writes:

> I don't quite understand how this works. Would you please write a
> small perl program which can print the two streams (with the following
> command) to help me understand it?
>
> example.pl <(cat a.txt) <(cat b.txt)

makholm(a)makholm:/tmp$ perl ./example.pl <(cat example.pl) <(tr 'a-zA-Z' 'n-za-mN-ZA-M' < example.pl)
001: #!/usr/bin/perl
001:
001: use strict;
001: use warnings;
001:
001: my $fileno;
001: for my $file (@ARGV) {
001: $fileno++;
001: open my $fh, "<", $file
001: or next;
001:
001: printf "%03d: %s", $fileno, $_ while <$fh>;
001: }
001:
001: __END__
002: #!/hfe/ova/crey
002:
002: hfr fgevpg;
002: hfr jneavatf;
002:
002: zl $svyrab;
002: sbe zl $svyr (@NETI) {
002: $svyrab++;
002: bcra zl $su, "<", $svyr
002: be arkg;
002:
002: cevags "%03q: %f", $svyrab, $_ juvyr <$su>;
002: }
002:
002: __RAQ__
makholm(a)makholm:/tmp$

//Makholm
From: John Bokma on 1 Jun 2010 09:48
Peng Yu <pengyu.ut(a)gmail.com> writes:

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

Also add this one:

use strict;

> use warnings;

> open(IN1, $ARGV[0]);


Use the 3 argument version of open, and it's often a very good idea to
report if the file actually couldn't be opened for reading:

open my $fh, '<', $ARGV[0]
or die "Can't open '$ARGV[0]' for reading: $!";
^--- explains why

--
John Bokma j3b

Hacking & Hiking in Mexico - http://johnbokma.com/
http://castleamber.com/ - Perl & Python Development
From: Martijn Lievaart on 1 Jun 2010 13:22
On Tue, 01 Jun 2010 02:26:59 -0700, Peng Yu wrote:

> 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?

It actually gets passed to your program as a filename, although it really
is a pipe to the command between the brackets.

[martijn(a)cow t]$ perl -e 'print "@ARGV\n"' <(cat t.pl) <(cat t.pl~)
/proc/self/fd/63 /proc/self/fd/62
[martijn(a)cow t]$

HTH,
M4
From: C.DeRykus on 2 Jun 2010 06:35
On Jun 1, 2:26 am, Peng Yu <pengyu...(a)gmail.com> wrote:
> On Jun 1, 3:24 am, Martijn Lievaart <m...(a)rtij.nl.invlalid> wrote:
>
....
>
> #!/usr/bin/env perl
>
> use warnings;
>
> open(IN1, $ARGV[0]);
> open(IN2, $ARGV[1]);
>
> while(<IN1>) {
>   print
>
> }
>
> print "------\n";
>
> while(<IN2>) {
>   print
>
> }
>
>

Perl provides a handy command line shortcut
if that's all you need (perldoc perlrun):


perl -pwe 'print "------\n" if eof' file1 file2 ...

--
Charles DeRykus

From: chad on 2 Jun 2010 11:08
On Jun 1, 10:22 am, Martijn Lievaart <m...(a)rtij.nl.invlalid> wrote:
> On Tue, 01 Jun 2010 02:26:59 -0700, Peng Yu wrote:
> > 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?
>
> It actually gets passed to your program as a filename, although it really
> is a pipe to the command between the brackets.
>
> [martijn(a)cow t]$ perl -e 'print "@ARGV\n"' <(cat t.pl) <(cat t.pl~)
> /proc/self/fd/63 /proc/self/fd/62
> [martijn(a)cow t]$
>

Why do you use the brackets in '<(cmd)'? Ie, why can't you just do
something like '<cmd' ?
First  |  Prev  |  Next  |  Last
Pages: 1 2 3
Prev: How to generate random number without replacement?
Next: FAQ 4.76 How do I verify a credit card checksum?