how to copy just part of a file?

[Mikko Työläjärvi]

On Wed, 16 Jul 2003, BSD baby wrote:

> Is there an easy built-in way to copy only part of a file?
>
> I want to take a WAV audio file and copy from #__ bytes to
> #___ bytes into a new file.
>
> (I'm making 30-second clips of files.)

Try "dd".  Thus:

  dd bs=1 skip=$offset count=$length < infile > outfile

It is possible that a block size of one byte is kind of inefficient,
so if you can operate in units of some larger size that might be good.
For example "bs=1k". See "man dd".

Also, remember that WAV files have a 44 byte (or was that 42...?) wav
header.  Yes, you can extract it with "dd bs=44 count=1", but I'm too
lazy to find out whether you can just prepend it to any split files
right now (i.e. if the file contains any length info; I suspect not).

> Though I found a scripting way to do it with PHP, I'm wondering
> if there's a more direct way to do it with basic GNU/BSD commands.

Ever heard of POSIX... ;-)

     $.02,
     /Mikko