Re: How come math/arithmetic cannot work by set -x
On 8/12/22 7:27 PM, Budi wrote: How come math/arithmetic ((i=k+l)) cannot make use of set -x If you're talking about what I think you are, because that's not how `set -x' works. It's the same reason that k=2+3 echo $(( $k*5 )) echo $(( k*5 )) produces two different numbers. -- ``The lyf so short, the craft so long to lerne.'' - Chaucer ``Ars longa, vita brevis'' - Hippocrates Chet Ramey, UTech, CWRUc...@case.eduhttp://tiswww.cwru.edu/~chet/
Re: How come math/arithmetic cannot work by set -x
On 8/12/22 8:22 PM, Dennis Williamson wrote:
set -x; unset a; b=2; c=7; ((a = b + c)); echo "$a $b $c"; set +x
+ unset a
+ b=2
+ c=7
+ (( a = b + c ))
+ echo '9 2 7'
9 2 7
+ set +x
without the dollar signs doesn't.
"Within an expression, shell
variables may also be referenced by name without using the parameter
expansion syntax. A shell variable that is null or unset evaluates to
0 when referenced by name without using the parameter expansion syntax.
The value of a variable is evaluated as an arithmetic expression when
it is referenced"
So this is the behavior of arithmetic expansion (and, as a consequence, the
execution of the `((' command) and `set -x' will not show it. `set -x'
displays the command and its arguments before it is executed.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRUc...@case.eduhttp://tiswww.cwru.edu/~chet/
Re: cut loadable outputs extra newlines
I note that https://pubs.opengroup.org/onlinepubs/009696699/utilities/cut.html says: *> The elements in list can be repeated, can overlap, and can be specified in any order, but the bytes, characters, or fields selected shall be written in the order of the input data.* The intention behind this is so that cut can be implemented as a small state machine using just getchar, putchar, and a counter. This avoids copying via a line buffer, and that implies there should be no line-length limit. So I'm a bit surprised that any kind of "getline" is used by the loadable version. -Martin PS: Other equivalent implementations are possible that can also avoid the stdio buffer copies.
Re: cut loadable outputs extra newlines
On Sat, Aug 13, 2022, at 10:06 PM, Martin D Kealey wrote: > I note that > https://pubs.opengroup.org/onlinepubs/009696699/utilities/cut.html says: > *> The elements in list can be repeated, can overlap, and can be specified > in any order, but the bytes, characters, or fields selected shall be > written in the order of the input data.* > > The intention behind this is so that cut can be implemented as a small > state machine using just getchar, putchar, and a counter. This avoids > copying via a line buffer, and that implies there should be no line-length > limit. That is explicitly required: INPUT FILES The input files shall be text files, except that line lengths shall be unlimited. -- vq
