I would use a digest not of the file content, but of the file name (computationally cheaper and no collisions possible).

What makes you think that a filename has the special property of returning a unique value for each and every hash function? Hash functions always have collisions, by definition. You can't losslessly compress arbitary amounts of data into 128, 256 or 512 bits. Sure, it is unlikely that two short names share the same hash value, but it is not impossible. And with filenames near MAX_PATH, which is 4 KBytes on Linux and perhaps even larger on other systems, collisions become more likely.

If you are on a unix-filesystem I would use the inode-number of the file (you get that with stat).

The inode is not unique, it is just unique per filesystem. Together with the device number, it should be unique. Problems start when the filesystem layer of the OS kernel has to invent inode numbers for filesystems that do not have inodes. Linux does that for at least the FAT-based filesystems, in linux/fs/fat/inode.c.

Alexander

--
Today I will gladly share my knowledge and experience, for there are no sweeter words than "I told you so". ;-)

In reply to Re^3: Renaming an image file by afoken
in thread Renaming an image file by Anonymous Monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.