Re^3: Looking for suitable spells to get open to return a filehandle from a module

What is the effect of the invocation of Symbol::gensym? This code seems to work just fine without it both with aliasing and with an automatic reference via a prototype (also minimally tested):
t_extra_open.pl:

use warnings;
use strict;

use Extra;

{
    my $filename = 'extra-open.txt';

    Extra::open my $fh, '>', $filename
        or die "opening '$filename' for write: $!";
    defined $fh or die "write filehandle not defined";
    print $fh "Extra open works just fine \n";
    print $fh "at ", scalar(localtime), "\n";
    close $fh or die "closing '$filename' after write";

    undef $fh;
    Extra::open $fh, '<', $filename
        or die "opening '$filename' for read: $!";
    defined $fh or die "read filehandle not defined";
    print '<<', <$fh>, '>>';
    close $fh or die "closing '$filename' after read";

}
[download]

Extra.pm:

package Extra;

sub open {  # works

    my (undef, $direction, $filename) = @_;

    return open $_[0], $direction, $filename;

    }

# sub open (\$@) {  # works
#
#     my ($sr_fh, $direction, $filename) = @_;
#
#     return open $$sr_fh, $direction, $filename;
#
#     }

1;
[download]

(Tested under ActiveState 5.8.9 and Strawberry 5.14.4.1.)

Give a man a fish: <%-{-{-{-<

Comment on Re^3: Looking for suitable spells to get open to return a filehandle from a module Select or Download Code

Replies are listed 'Best First'.
Re^4: Looking for suitable spells to get open to return a filehandle from a module by afoken (Chancellor) on Dec 03, 2016 at 16:58 UTC
What is the effect of the invocation of `Symbol::gensym`? In this case, just a lazily copied expression. Quoting Symbol: `Symbol::gensym` creates an anonymous glob and returns a reference to it. Such a glob reference can be used as a file or directory handle. And that's it. It was needed in ancient perls. Perl 5.6.1 introduced autovivication for file and directory handles (see perl561delta), so `Symbol::gensym` is technically no longer needed. `open my $fh, ...` or `open local $fh, ...` is sufficient. Alexander -- Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)	[reply] [d/l] [select]
Re^5: Looking for suitable spells to get open to return a filehandle from a module by pryrt (Abbot) on Dec 05, 2016 at 21:40 UTC
... so `Symbol::gensym` is technically no longer needed But there are times when it's still useful... like when you want `open3()` to keep STDOUT and STDERR separate (by default, if you pass it undef for both STDOUT and STDERR, STDERR will be directed to the same filehandle that's created for STDOUT) #!/usr/bin/env perl use warnings; use strict; use IPC::Open3; use Symbol qw(gensym); use POSIX qw(:sys_wait_h); # I'm sometimes using perl 5.8.5, so //'<undef>' unavailable # verified later on 5.14.2 sub defor($) { defined($_[0]) ? $_[0] : '<undef>' } foreach my $run (1..3) { my ($out, $err) = ('',''); my ($fhi, $fho, $fhe) = ($run == 1) ? (undef, undef, undef) : # when fhe==un +def goes to open3, STDERR will be redirected to STDOUT ($run == 2) ? (undef, undef, gensym) : # this keeps S +TDERR and STDOUT separate (gensym, gensym, gensym) ; # as does this +, the first two gensym are unecessary, but the third is needed my $pid = open3( $fhi, $fho, $fhe, qq[cat - ; perl -le 'print STDE +RR "this should be STDERR (run#$run)...\nand so should this (run#$run +)\n"'] ); print { $fhi } "[run#$run] This should be STDOUT\n"; close($fhi); $out .= join '', map { s/^/STDOUT> / if $_ ne $/; $_ } readline($f +ho) if defined $fho; $err .= join '', map { s/^/STDOUT> / if $_ ne $/; $_ } readline($f +he) if defined $fhe; print "Read STDOUT:\n$out\n" if length($out); print "Read STDERR:\n$err\n" if length($err); printf "run#%d --- fhi='%s' fho='%s' fhe='%s'\n", $run, defor $fhi +, defor $fho, defor $fhe; print "="x75, "\n\n"; } __END__ Read STDOUT: STDOUT> [run#1] This should be STDOUT STDOUT> this should be STDERR (run#1)... STDOUT> and so should this (run#1) run#1 --- fhi='GLOB(0x92fdba4)' fho='GLOB(0x92fdbcc)' fhe='<undef>' ====================================================================== +===== Read STDOUT: STDOUT> [run#2] This should be STDOUT Read STDERR: STDOUT> this should be STDERR (run#2)... STDOUT> and so should this (run#2) run#2 --- fhi='GLOB(0x93811c0)' fho='GLOB(0x932bc60)' fhe='GLOB(0x92fd +ba4)' ====================================================================== +===== Read STDOUT: STDOUT> [run#3] This should be STDOUT Read STDERR: STDOUT> this should be STDERR (run#3)... STDOUT> and so should this (run#3) run#3 --- fhi='GLOB(0x93811c0)' fho='GLOB(0x932bc60)' fhe='GLOB(0x92fd +ba4)' ====================================================================== +===== [download] Yes, I know the OP didn't include `open3`, but since I was recently learning the ins and outs of open3 filehandles, I thought I'd mention this exception to your general rule, for posterity's sake.	[reply] [d/l] [select]