21 Jun
2021
21 Jun
'21
3:37 p.m.
Hello,
I'm currently trying out the rc shell (using Byron Rakitzis'
implementation for Unix). Compared to Bash, which I normally use, this
shell has a rather small feature set (which isn't to say that that's
necessarily a bad thing).
Now, one of the features that Bash has and rc doesn't have is the
ability to perform arithmetic expansion. That's not really a problem
because you can just use `expr` instead. I wonder, though, when
arithmetic expansion as a shell built-in became a thing, especially in
POSIX sh.
POSIX has included that feature since at least 2001, and probably quite
some years earlier, given that Bash already had it in 1995 (going by
the manual page of version 1.14.7, the oldest I could find).
So, maybe someone here can help me find out when this was actually
standardized.
Thanks.
--
Michael
21 Jun
21 Jun
3:57 p.m.
Arithmetic expansion dates back at least as far as ksh88.
Bash likely picked it up from there.
The original was only integer math and Bash remains that way (IIRC,
Chet can correct me if I'm wrong). ksh93 added floating point math.
POSIX would have picked it up from ksh88.
HTH,
Arnold
Michael Siegel <msi(a)malbolge.net> wrote:
Hello,
I'm currently trying out the rc shell (using Byron Rakitzis'
implementation for Unix). Compared to Bash, which I normally use, this
shell has a rather small feature set (which isn't to say that that's
necessarily a bad thing).
Now, one of the features that Bash has and rc doesn't have is the
ability to perform arithmetic expansion. That's not really a problem
because you can just use `expr` instead. I wonder, though, when
arithmetic expansion as a shell built-in became a thing, especially in
POSIX sh.
POSIX has included that feature since at least 2001, and probably quite
some years earlier, given that Bash already had it in 1995 (going by
the manual page of version 1.14.7, the oldest I could find).
So, maybe someone here can help me find out when this was actually
standardized.
Thanks.
--
Michael
7:50 p.m.
On 6/21/21 5:57 AM, arnold(a)skeeve.com wrote:
Arithmetic expansion dates back at least as far as
ksh88.
ksh had the `let' builtin from at least 1983. The ((...)) compound command
was there by ksh-86.
Bash likely picked it up from there.
Sort of, see below.
The original was only integer math and Bash remains
that way (IIRC,
Chet can correct me if I'm wrong). ksh93 added floating point math.
Yes, bash only has integer arithmetic, since it's all POSIX requires.
POSIX would have picked it up from ksh88.
The $((...)) form of arithmetic expansion is something POSIX picked up
from ksh-88, eventually. The early drafts of the standard (through 1003.2
d9, at least), used $[...], but they eventually adopted $((...)) because
ksh-88 had already implemented it, though it's not documented in Bolsky
and Korn.
I put $[...] into bash first (it's still there, though deprecated), then
`let', then $((...)) after POSIX added it, and finally `((' for
compatibility.
Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU chet(a)case.edu http://tiswww.cwru.edu/~chet/
8:43 p.m.
Am Mon, 21 Jun 2021 09:50:38 -0400
schrieb Chet Ramey <chet.ramey(a)case.edu>du>:
The $((...)) form of arithmetic expansion is something
POSIX picked up
from ksh-88, eventually. The early drafts of the standard (through
1003.2 d9, at least), used $[...], but they eventually adopted
$((...)) because ksh-88 had already implemented it, though it's not
documented in Bolsky and Korn.
So, in other words, POSIX shell (meaning the shell described in the
standard as it has been released) had double-parentheses arithmetic
evaluation from the start?
--
Michael
8:48 p.m.
On 6/21/21 10:43 AM, Michael Siegel wrote:
Am Mon, 21 Jun 2021 09:50:38 -0400
schrieb Chet Ramey <chet.ramey(a)case.edu>du>:
From the first published version of the standard, yes.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU chet(a)case.edu http://tiswww.cwru.edu/~chet/
The $((...)) form of arithmetic expansion is
something POSIX picked up
from ksh-88, eventually. The early drafts of the standard (through
1003.2 d9, at least), used $[...], but they eventually adopted
$((...)) because ksh-88 had already implemented it, though it's not
documented in Bolsky and Korn.
So, in other words, POSIX shell (meaning the shell described in the
standard as it has been released) had double-parentheses arithmetic
evaluation from the start?
22 Jun
22 Jun
10:24 p.m.
Am Mon, 21 Jun 2021 10:48:18 -0400
schrieb Chet Ramey <chet.ramey(a)case.edu>du>:
On 6/21/21 10:43 AM, Michael Siegel wrote:
Thanks. This will spare me from putting yet another footnote into my
little review of rc(1).
--
Michael
So, in other words, POSIX shell (meaning the
shell described in the
standard as it has been released) had double-parentheses arithmetic
evaluation from the start?
From the first published version of the standard, yes.
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Michael Siegel