For a regular file st_rdev is 0, for a device file (e.g. /dev/tty) it holds the major and minor device numbers (assuming a POSIX like system) which can derived by masking and shifting appropriately. You can see how this is done in the source of File::Stat::Bits. The following is derived from that module: 

my $tty_rdev = (stat('/dev/dsp0'))[6];
 
print  major($tty_rdev), " ", minor($tty_rdev),"\n";
 
sub MAJOR_MASK   () { 03777400 }
sub MAJOR_SHIFT  () { 0000010 }
sub MINOR_MASK   () { 037774000377 }
sub MINOR_SHIFT  () { 0000000 }
 
sub major
{
    my $dev = shift;
 
 
    return defined MAJOR_MASK ? ($dev & MAJOR_MASK) >> MAJOR_SHIFT : u
+ndef;
}
 
 
 
sub minor
{
    my $dev = shift;
 
 
    return defined MINOR_MASK ? ($dev & MINOR_MASK) >> MINOR_SHIFT : u
+ndef;
}

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If you want to recreate the st_rdev from the output of the stat command you want to get the values for the major and minor device type and combine them using the dev_join from File::Stat::Bits.

I'm not clear however why you want to use the external command rather than the builtin stat.

/J\

In reply to Re: Meaning of stat's 'rdev' value. by gellyfish
in thread Meaning of stat's 'rdev' value. by palamedes

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