sub is_FH_a_wrapped_scalar {
my $FH = shift;
return grep { $_ eq "scalar} } PerlIO::get_layers($FH);
}
This uses PerlIO to find the layers of I/O handlers on your filehandle. If one of them is named "scalar", then the filehandle is ultimately wrapping a scalar variable.
Unfortunately, this is the only way I've found to do it, and PerlIO might not be compiled in all versions you use.
$ perl pm_1214805.pl
FH is a wrapped scalar, do something else!
<read><5></etc/>
<sysread><5><SYSTE>
<read><5><SYSTE>
$ cat pm_1214805.pl
#!/usr/bin/perl
use strict;
use warnings;
sub is_fh_a_wrapped_scalar {
my $fh = shift;
my @layers = PerlIO::get_layers($fh);
return grep { $_ eq "scalar" } @layers;
}
sub dbg {
my ($op, $fh, $rc, $scalar) = @_;
$rc = "UNDEF" unless defined $rc;
print "<$op><$rc><$scalar>\n";
close $fh or die;
}
sub doit_read {
my ($fh) = @_;
my $rc = read $fh, my $scalar, 5;
dbg "read", $fh, $rc, $scalar;
}
sub doit_sysread {
my ($fh) = @_;
if (is_fh_a_wrapped_scalar($fh)) {
print "FH is a wrapped scalar, do something else!\n";
}
else {
my $rc = sysread $fh, my $scalar, 5;
dbg "sysread", $fh, $rc, $scalar;
}
}
my $fh;
open $fh, "<", \"/etc/passwd" or die; doit_sysread $fh;
open $fh, "<", \"/etc/passwd" or die; doit_read $fh;
open $fh, "<", "/etc/passwd" or die; doit_sysread $fh;
open $fh, "<", "/etc/passwd" or die; doit_read $fh;
...roboticus
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