3-argument open on STDIN

How can I do a 3-argument open on STDIN? This doesn't work because the
3-argument open won't open STDIN when you tell it to open "-".

**************************************
@files = ("-");

for (@files) {
print reverse readfile($_);
}

sub readfile {

open(my $fh,"<",$_[0]) or die "$me: Couldn't open $_[0]: $!\n";
my(@fc) = <$fh>;
close($fh) or die "$me: Couldn't close $_[0]: $!\n";
if ($fc[0] =~ /\r/) { @fc = map { s/\r\n?/\n/g; split /(?<=\n)/ } @fc; }
if (wantarray()) { return @fc; }
else { return join('', @fc) }
}
**************************************

How can I use the "safe" 3-argument open and still be able to read off a
pipe?

- Bryan




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Re: 3-argument open on STDIN

On Wed, Aug 17, 2011 at 6:53 PM, Bryan R Harris
wrote:
> How can I use the "safe" 3-argument open and still be able to read off a
> pipe?

What I have done in the past is manually compare the filename to '-'
and skip the opening and just assign STDIN to my file handle.

use strict;
use warnings;

my @filenames = qw(-);

@filenames = @ARGV if @ARGV;

for my $filename (@filenames)
{
my $fh;

if($filename eq '-')
{
$fh = \*STDIN;
}
else
{
open $fh, '<', $filename or die "Failed to open '$filename': $!";
}

# Etc...
}

__END__

Perhaps experienced Perl programmers know of better ways, in which
case I would be happy to learn them also. :)


--
Brandon McCaig
V zrna gur orfg jvgu jung V fnl. Vg qbrfa'g nyjnlf fbhaq gung jnl.
Castopulence Software

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Re: 3-argument open on STDIN

At 17:53 -0500 17/08/2011, Bryan R Harris wrote:


>How can I do a 3-argument open on STDIN? This doesn't work because the
>3-argument open won't open STDIN when you tell it to open "-".
>
>**************************************
>@files = ("-");
>
>for (@files) {
> print reverse readfile($_);
>}
>[...]


That makes no sense to me at all. I see no mention of STDIN in the
script and see you are trying to open and read a single file named
"-", which is pretty odd.

If this below is your script "test.pl" and you run it from the
Terminal or command line...


#!/usr/bin/perl
use strict;
use warnings;
print "Enter file names separated by space\n--> ";
my @files = split /\s+/, ;
foreach my $file (@files){
undef my @lines;
open my $fh, "<$file" or die $!;
print "\n____File: $file\____\n";
while (<$fh>){
chomp;
unshift @lines, $_;
}
for (@lines){
print "$_\n";
}
}
END


This is what you will get:


>>> perl test.pl
Enter file names separated by space
--> a.txt b.txt c.txt

____File: a.txt____
e
d
c
b
a

____File: b.txt____
j
i
h
g
f

____File: c.txt____
o
n
m
l
k

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Re: 3-argument open on STDIN

On 18/08/2011 01:35, John Delacour wrote:
> At 17:53 -0500 17/08/2011, Bryan R Harris wrote:
>
>
>> How can I do a 3-argument open on STDIN? This doesn't work because the
>> 3-argument open won't open STDIN when you tell it to open "-".
>>
>> **************************************
>> @files = ("-");
>>
>> for (@files) {
>> print reverse readfile($_);
>> }
>> [...]
>
>
> That makes no sense to me at all. I see no mention of STDIN in the
> script and see you are trying to open and read a single file named "-",
> which is pretty odd.

Hi John

Bryan is referring to a poorly-documented feature of Perl, which as far
as I know is only described in perldoc perlopentut. This is what it says:

> The Minus File
> Again following the lead of the standard shell utilities, Perl's "open"
> function treats a file whose name is a single minus, "-", in a special
> way. If you open minus for reading, it really means to access the
> standard input. If you open minus for writing, it really means to access
> the standard output.

And the problem is that, while

open my $fh, '-';

or

open my $fh, '<-';

opens a copy of the STDIN filehandle, the three-argument form of open

open my $fh, '<', '-';

looks instead for a real file called '-' and fails if it doesn't find
one. Brandon's solution is the only one I can think of.

Rob

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Re: 3-argument open on STDIN

On 11-08-17 06:53 PM, Bryan R Harris wrote:
>
>
> How can I do a 3-argument open on STDIN? This doesn't work because the
> 3-argument open won't open STDIN when you tell it to open "-".
>
> **************************************
> @files = ("-");
>
> for (@files) {
> print reverse readfile($_);
> }
>
> sub readfile {
>
> open(my $fh,"<",$_[0]) or die "$me: Couldn't open $_[0]: $!\n";
> my(@fc) =<$fh>;
> close($fh) or die "$me: Couldn't close $_[0]: $!\n";
> if ($fc[0] =~ /\r/) { @fc = map { s/\r\n?/\n/g; split /(?<=\n)/ } @fc; }
> if (wantarray()) { return @fc; }
> else { return join('', @fc) }
> }
> **************************************
>
> How can I use the "safe" 3-argument open and still be able to read off a
> pipe?
>
> - Bryan
>
>
>
>

Well, this doesn't use the 3-argument open but it gets the job done.

#!/usr/bin/env perl

use strict;
use warnings;

my @files = ( $0, '-', $0 );

for my $file ( @files ){
print reverse readfile( $file );
}

sub readfile {
local @ARGV = @_;
my ( @fc ) = <>;

# as above

return wantarray ? @fc : join( '', @fc );
}

__END__


--
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as it is about coding.

The secret to great software: Fail early & often.

Eliminate software piracy: use only FLOSS.

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