Return to Revisions

Please try your yes thing again with an actual blocking factor. Like:

yes | dd ibs=k obs=kxk |
dd bs=kxk count=10 of=out

If you have a POSIX dd on site, your results will be:

10+0 records in
10+0 records out
10485760 bytes (10 MB) copied, 0.127955 s, 81.9 MB/s
$ ls -l out
-rw-r--r-- 1 mikeserv mikeserv 10485760 Mar 23 17:37 out

You have to synchronize i/o w/ dd to handle non-seekable inputs. In other words, make pipe-buffers explicit and they cease to be a problem. That's what dd is for. I suggest you read through the POSIX spec on dd. Particularly important is that you learn the different implications of any declarations for [ioc]?bs=. Here's a snippet from the POSIX spec:

• ibs=expr
  • Specify the input block size, in bytes, by expr (default is 512).
• obs=expr
  • Specify the output block size, in bytes, by expr (default is 512).
• bs=expr
  • Set both input and output block sizes to expr bytes, superseding ibs= and obs=. If no conversion other than sync, noerror, and notrunc is specified, each input block shall be copied to the output as a single block without aggregating short blocks.

You'll also find some of this explained better here.