Re: Kludge for handling REPL arithmetic expressions

[Greg Wooledge]

On Wed, Aug 04, 2021 at 11:12:01AM +0100, Chris Elvidge wrote:
> I was intrigued by this. So tried:
> =() { echo "scale=5; $@" | bc; }

I'd suggest $* here.  You don't really want to preserve separate
arguments in this case.

Also, you really want bc -l, which also means you really don't want
to reduce the scale to merely 5.  (If you want to reduce the
percision of the answer, capture it with a command substitution, and
then feed it to printf for rounding.  Reducing the scale within bc
leads to extremely wrong answers in some cases.)

> Seems to work for simple calculations.
> 
> A couple of questions, though.
> 1) How do you 'export -f ='? Or is it impossible?

Probably impossible, as it is an invalid shell "identifier".

> 2) How do you type in '= log(2048,2)' without getting a syntax error?

With quotes.  Also, "log()" is spelled "l()" in bc.

unicorn:~$ =() { echo "$*" | bc -l; }
unicorn:~$ = 'l(2048.2)'
7.62471663764133723968

Or with rounding:

unicorn:~$ =() { local n; n=$(echo "$*" | bc -l) || return; printf '%.5f\n' 
"$n"; }
unicorn:~$ = 'l(2048.2)'
7.62472

This is a cute little experiment, but it's not a path I'd choose for
myself.  What I do instead is keep a dedicated terminal window open
in a specific spot on my screen, with bc -l running interactively.
If I need to calculate something, I just focus on that window and type
my expressions there.

Also, I guess checking bc's exit status is pointless...

unicorn:~$ = 1/0
Runtime error (func=(main), adr=3): Divide by zero
0.00000
unicorn:~$ echo '1/0' | bc -l
Runtime error (func=(main), adr=3): Divide by zero
unicorn:~$ echo $?
0

*sigh*