On Mon, Mar 27, 2006 at 05:33:48AM +0400, Solar Designer wrote: [...] > POSIX.1-2001 does not appear to explicitly specify the behavior of > skip= with partial reads. It defines skip= as follows: > > skip=n > Skip n input blocks (using the specified input block size) > before starting to copy. On seekable files, the implementation > shall read the blocks or seek past them; on non-seekable files, > the blocks shall be read and the data shall be discarded. > > However, it gives this example: > > The following command: > > dd ibs=10 skip=1 > > strips the first 10 bytes from standard input. > > Notice that they said "the first 10 bytes", with no exceptions - does > this mean that this command should skip the first 10 bytes even if the > first read() returns only 5 bytes?
Here is a simple test case to illustrate the issue: $ echo 123456789 |dd ibs=10 skip=1 0+0 records in 0+0 records out 0 bytes (0 B) copied, 2e-05 seconds, 0 B/s $ (echo -n 12345; /bin/true; echo 6789) |dd ibs=10 skip=1 6789 0+1 records in 0+1 records out 5 bytes (5 B) copied, 0.000253 seconds, 19.8 kB/s -- ldv
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