On Thu, Feb 16, 2017 at 7:49 PM, scott Ford <[email protected]> wrote:
> You guys are amazing. I havent used Unix on Z/OS much, a little. It has
> advantages for sure.
>
> Scott
>
>
It adds some really nice features to legacy z/OS. But UNIX files can be
confusing to z/OS programmers because they are more like "memory" than
"disk" in that they are simply an ordered sequence of _bytes_, not
_records_. The file system itself does not have _any_ interpretation of
how those bytes are grouped into logical records. z/OS programmers, in
general, are used to reading individual records when reading a data set.
When you read a UNIX file, the program must tell the UNIX kernel ("access
method") how many bytes you want to read. UNIX will return __NO MORE__ than
that number of bytes. It could return fewer, if there are not that many
left before "end of file" (an on some other rare occasions). Your code must
then somehow know where the data you want (aka "this record") ends. Which
means either the file is composed of fixed length records, hard coded in
the program, or there is meta information encoded in the file data itself
which indicates a length (similar to the LLBB field in a z/OS variable
length data set) for each record. You can't rely on the system "handing"
you a "logical record: when you do a UNIX read simply because there is no
such thing, in a general sense.
The main drawback to z/OS UNIX is the relatively extreme overhead of doing
a fork() or spawn(). UNIX shells do those by the _ton_. Which explains the
BPXAS instances, which are the UNIX equivalent of a WLM batch initiator
(even runs the same program, IEFIIC, just with a special PARM= value).
Another drawback, to me, of z/OS UNIX is that the supplied UNIX tools (like
awk, find and /bin/sh) are _not_ as good as the GNU versions. Thankfully
Rocket Software has stepped into the gap with a nice port of many of them
for _no cost_, with optional paid support.
--
"Irrigation of the land with seawater desalinated by fusion power is
ancient. It's called 'rain'." -- Michael McClary, in alt.fusion
Maranatha! <><
John McKown
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