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oct function in perl

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Old 05-04-2009
oct function in perl
hi

i came across one program which uses some method to calculate file permissions using lstat in perl and i am not getting how its doing that i am pasting the code below ...

Code:
$ > cat b.pl
use Fcntl':mode';
my ($dev,$ino,$mode,$nlink,$uid,$gid,$rdev,$size,$atime,$mtime,$ctime,$blksize,$blocks) = lstat($ARGV[0]);
my $perms = S_IMODE($mode);
print "perm : [$perms]\n" ;
my $a = ~oct('055') ;
my $b = oct('777') ;
my $c = ( $a & $b ) ;
print "[$a][$b][$c]\n" ;
$umask = "055" ;
if ( $umask ) {
                $perms = S_IMODE($perms & (~oct($umask) & oct('777')));
                print "perm now : [$perms]\n" ;
              }


output :

perm : [493]
[4294967250][511][466]
perm now : [448]

i am not getting the part which in red colour...

can any one explain this part to me ??
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LEARN ABOUT FREEBSD

dh_perl

DH_PERL(1)							     Debhelper								DH_PERL(1)

NAME

       dh_perl - calculates Perl dependencies and cleans up after MakeMaker

SYNOPSIS

       dh_perl [debhelperoptions] [-d] [librarydirs...]

DESCRIPTION

       dh_perl is a debhelper program that is responsible for generating the ${perl:Depends} substitutions and adding them to substvars files.

       The program will look at Perl scripts and modules in your package, and will use this information to generate a dependency on perl or
       perlapi. The dependency will be substituted into your package's control file wherever you place the token ${perl:Depends}.

       dh_perl also cleans up empty directories that MakeMaker can generate when installing Perl modules.

OPTIONS

       -d  In some specific cases you may want to depend on perl-base rather than the full perl package. If so, you can pass the -d option to make
	   dh_perl generate a dependency on the correct base package. This is only necessary for some packages that are included in the base
	   system.

	   Note that this flag may cause no dependency on perl-base to be generated at all. perl-base is Essential, so its dependency can be left
	   out, unless a versioned dependency is needed.

       -V  By default, scripts and architecture independent modules don't depend on any specific version of perl. The -V option causes the current
	   version of the perl (or perl-base with -d) package to be specified.

       library dirs
	   If your package installs Perl modules in non-standard directories, you can make dh_perl check those directories by passing their names
	   on the command line. It will only check the vendorlib and vendorarch directories by default.

CONFORMS TO

       Debian policy, version 3.8.3

       Perl policy, version 1.20

SEE ALSO

       debhelper(7)

       This program is a part of debhelper.

AUTHOR

       Brendan O'Dea <bod@debian.org>

11.1.6ubuntu2							    2018-05-10								DH_PERL(1)