12-27-2019
Hi Ravinder,
As long as a mv operation is performed on the same file system - as is the case here - that should not pose a problem, since mv then only manipulates directory data: A file name is nothing more than a directory entry, a pointer (a hard link) to the file itself.
When a process opens a file for reading, the operation system creates an entry (file descriptor) to represent that file and stores information about that opened file in memory. So then the directory entry is no longer used.
The mv operation is thus free to manipulate the directory entry.
So for the process that has opened and is reading the file, nothing changes as the directory data is being changed.
When it is done reading it just closes the file descriptor.
Also, the file list expanded by the glob is expanded before being passed to the awk script, so new file names are not passed to the script.
S.
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LEARN ABOUT ULTRIX
getdirentries
getdirentries(2) System Calls Manual getdirentries(2)
Name
getdirentries - gets directory entries in a generic directory format
Syntax
#include <sys/dir.h>
cc = getdirentries(fd, buf, nbytes, basep)
int cc, fd;
char *buf;
int nbytes;
long *basep;
Description
The system call puts directory entries from the directory referenced by the file descriptor fd into the buffer pointed to by buf, in a
generic directory format. Up to nbytes of data are transferred. The nbytes of data must be greater than or equal to the block size asso-
ciated with the file. For further information, see Sizes less than nbytes can cause errors on certain file systems.
The data returned in the buffer is a series of direct structures, each containing the following entries:
unsigned long d_ino;
unsigned short d_reclen;
unsigned short d_namlen;
char d_name[MAXNAMLEN + 1];
The d_ino entry is a number that is unique for each distinct file in the file system. Files that are linked by hard links have the same
d_ino . For further information, see The d_reclen entry is the length, in bytes, of the directory record. The d_namlen entry specifies
the length of the file name. The d_name entry contains a null-terminated file name. Thus, the actual size of d_name can vary from 2 to
MAXNAMLEN + 1.
The generic directory structures are not necessarily tightly packed. The d_reclen entry may be used as an offset from the beginning of a
direct structure to the next structure, if any.
Upon return, the actual number of bytes transferred is returned. The current position pointer associated with fd is set to point to the
next block of entries. The pointer is not necessarily incremented by the number of bytes returned by If the value returned is zero, the
end of the directory has been reached. The current position pointer may be set and retrieved by The system call writes the position of the
block read into the location pointed to by basep. It is not safe to set the current position pointer to any value other than a value pre-
viously returned by or a value previously returned in the location pointed to by basep or zero.
Return Values
If successful, the number of bytes actually transferred is returned. Otherwise, a -1 is returned and the global variable errno is set to
indicate the error.
Diagnostics
The system call fails under the following conditions:
EBADF The fd is not a valid file descriptor open for reading.
ENOTDIR The fd is not a directory.
EFAULT Either buf or basep points outside the allocated address space.
EIO While reading from or writing to the file system, an I/O error occurred.
EINTR A read from a slow device was interrupted by the delivery of a signal before any data arrived.
EPERM The user does not have read permission in the directory. The system call is not the suggested interface for reading direc-
tories. The and routines offer a standard interface. See the reference page for information on these routines.
See Also
close(2), link(2), lseek(2), open(2), stat(2), directory(3)
getdirentries(2)