Everything is a file?

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# 1  
Old 11-10-2009
Everything is a file?

In Unix, If everything is treated as a file is true(so directory is also a file)

Can we print the directory like printing the file?
# 2  
Old 11-10-2009
What do you think?
# 3  
Old 11-10-2009
Actually it depends on the OS and version.

The old "everything is a file" is becoming a little less true than it used to be.

In the olden days, I could "od ." on any Unix system and see the actual directory entries. Most today will fail, telling you what you probably already know
od: .: Is a directory

Typically, the reason for doing this was to either to see the order of the files in the directory (so you could tell how far along a backup or restore was that you were watching on another screen) or to look for "holes" (so that you could rearrange the order of entries by judicious copying and deleting). Why would you want to do that? If you have to ask, you'll probably never want to, but in some situations involving large directories and ultra critical performance, it's worth moving frequently accessed files to the "top", (assuming the namei cache can't help you, perhaps because you need that boost on the *first* access).

Yet another reason was to spot garbage characters in file names.

If all you need is the order of file names in the slots, ls -f will do it.

You can write your own program. I did this on a SCO Unix system:

#include <dirent.h>
#include <stdio.h>
DIR *dirp;
char *c;
long offset=0L;
struct dirent *dp;
dirp = opendir( "." );
while ( (dp = readdir( dirp )) != NULL )
        printf("Inode: %8lu Offset %4ld Length %4hd ", dp->d_ino,offset,dp->d_reclen);
        printf("%s ",dp->d_name);
        offset = dp->d_off;
        while (*c)
        printf("%x ",*c++);

closedir( dirp );

You can add to this to display other information, of course, but while it does show the order, it doesn't show holes. You can infer holes from the directory size and offsets, and you can create holes where you want them by removing or copying files, but it's certainly true that an od on a directory was useful now and then.
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