Yes, 0170000 and 0007777 are octal masks, the first for file types, the second for permissions. Here is the complete list of masks and constants from 'man 2 stat':

  The following flags are defined for the st_mode field:

    S_IFMT     0170000   bitmask for the file type bitfields
    S_IFSOCK   0140000   socket
    S_IFLNK    0120000   symbolic link
    S_IFREG    0100000   regular file
    S_IFBLK    0060000   block device
    S_IFDIR    0040000   directory
    S_IFCHR    0020000   character device
    S_IFIFO    0010000   fifo
    S_ISUID    0004000   set UID bit
    S_ISGID    0002000   set GID bit (see below)
    S_ISVTX    0001000   sticky bit (see below)
    S_IRWXU    00700     mask for file owner permissions
    S_IRUSR    00400     owner has read permission
    S_IWUSR    00200     owner has write permission
    S_IXUSR    00100     owner has execute permission
    S_IRWXG    00070     mask for group permissions
    S_IRGRP    00040     group has read permission
    S_IWGRP    00020     group has write permission
    S_IXGRP    00010     group has execute permission
    S_IRWXO    00007     mask for permissions for others (not in group
+)
    S_IROTH    00004     others have read permission
    S_IWOTH    00002     others have write permisson
    S_IXOTH    00001     others have execute permission
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Octal is the popular notation for these, because sets of permissions occupy three bits.

After Compline,
Zaxo

I am wanting to see if my file is a link without having to rerun the stat operator. I saw an note in O'Reilly Perl book that stated that when returning info on a link, stat would return the filetype of the actual file (- , d, etc...). So maybe I should re-phrase my question to: Is there a way to have an algorithm that will tell me what type of file it is without having to check each specific bit. The following code returns a - for the file which is a link in both the $filelink and the $filetype variables.

# hard code a test link file to check
$source_file = "/temp/test/source/dir1/hello1_link.txt";

# define filetype array with potential first bits of mode
@ftypes  = qw(. p c ? d ? b ? - ? l ? s ? ? ?);
$ftypes0 = '';

# Get File Statistics Using Scalar context

($dev,$inode,$mode,$nlink,$uid,$gid,$rdev,$size,
 $atime,$mtime,$ctime,$blksize,$blocks) = stat($source_file);

$perms    = $mode & 07777;
$octperms = sprintf("%lo", $perms);
$filetype = $ftypes[($mode & 0170000)>>12];
$filelink = $ftypes[($mode & 0120000)>>12];
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And while I am admitting how much I don't know, what does the >>12 do in the array reference? Thanks.

I can answer the last part about the bit shift operator.
>> 12 takes the number to the left and shifts it 12 bits to the right.
<< 12 would shift it 12 bits to the left.
In octal there are 3 bits per character shown (is this still called a nibble? Or is that only 4 bits, I don't play in octal that often :)
So this will bitwise and $mode with 0170000 and then shift it down so that the bottom 4 zero's go away.
0170000 >> 12 = 017
Hope this helps!

You should use the lstat builtin if you don't want to resolve soft links.

If you use Fcntl qw(:mode); you can get the constants by name. That will be easier to read and remember.

++Helter for the other answers.

After Compline,
Zaxo

What does the $mode & 07777 do? Could you explain it in layman's terms. I am not familiar with this type of expression as I am very new to Perl.

I'm not sure there is a "laymans" terms explanation for this. A single & is a bitwise and. This means it will go through the left and right, compare them bit by bit and the result is determined by the and function:


src1   src2   dest
0      0      0
0      1      0
1      0      0
1      1      1
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In your example src1 is $mode, src2 is 07777 and dest is $perms. This is mostly used to zero out bits, or mask off portions of bits.
The bitwise or operator, |, is used to set bits in a bit-string.
Hope this helped.

The 7's in the two numbers seem to indicate a change of base to octal numbers. Unix permissions like 755 etc are quoted as base 8 octal numbers (as opposed to base 10 ie decimal). The rest seems to be a for the purposes of a mask.