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defines a handy function for quick calculations from cli.
once defined:
? 10*2+3
There are 3 alternatives - vote for the best!
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Another way to do that would be:
? () { let myresult="$*" ; echo $myresult; }
That would avoid changing context (launching a new process, that's what "bc" is) and would be much faster if you are using the calculations in some loop or whatever.
To ensure that, I made a quick test: I defined "?" as my function, and "x" as your function, and measured their times for a simple compound calculation:
time ( for a in {0..999}; do ? "($a*$a-$a)/($a+$a+1)" > /dev/null ; done )
real 0m0.767s
user 0m0.624s
sys 0m0.144s
time ( for a in {0..999}; do x "($a*$a-$a)/($a+$a+1)" > /dev/null ; done )
real 0m6.777s
user 0m1.544s
sys 0m4.548s
Of course, it might be that you would miss some functionality for advanced calculations using the internal shell syntax instead of bc. But then again, bc (-l or not) has its limitations: you can't use it for non-integer exponentials, that is:
echo "2^(1/3)" | bc -l
Runtime warning (func=(main), adr=9): non-zero scale in exponent
I would recommend installing the "concalc" package if you need better mathematical evaluations in shell commands:
echo "2^(1/3)" | concalc
1.25992104989487316
sweet! many uses for this, also thanks for concalc...
I prefer the Pari calculator which in this situation can be invoked as "gp -q". It gives you tons of functions and an obscene number of decimal points.
For some reason when I try to run the "?" function defined above I just get "bash: z: command not found" and for "help ?" I get "help: no help topics match `z'". Any ideas why?
@dstahlke this is because you have a file named z in the current directory, the shell expands ? to z, so you get this error message
As long as I've been bash'ing, I didn't know you could use
?
as a function name. Thanks for the example for that, even if I don't use the calculator function! :)
Is it actually necessary to define a function for "bc"?
It is simple enough to do this:
<<< "x=1; y=2; p=3*x+2*y; p" bc -l
you can use bash format for very simple calculations like
echo $[ 1*2 + 3 ]
5
bc <<< 10*2+3
Here is what I have defines: ? for bash arithmetic, calc for awk arithmetic, and a here-string for bc -l arithmetic:
# bash arithmetic
function ? { echo $[$*] }
# awk arithmetic (floating point result)
function calc(){ awk "BEGIN{ print $* }" ;}
bc -l<<<3/7
Different calculators for different levels:
bash for simplest integer operations:
echo $[2*(3+5)]
16
awk for floating point and powers
function ? { awk "BEGIN{ print $* }" ;}
? '((2+1)/7)^3.5'
0.0515325
concalc for full scientific functions:
concalc<<<'sin(32^(1/3))'
-0.0332033464121159848
bc for high precision:
bc -l<<<3/7
.42857142857142857142
gp for number theory:
gp -qf
2.6040699049291378729513930560926568818 E574964
Fixing that:
gp for number theory:
gp -qf
2.6040699049291378729513930560926568818 E574964
gp for number theory:
gp -qf<<<'123456! + 0.'
2.6040699049291378729513930560926568818 E574964
Now if anyone has a way to delete or modify typos in comments, please let me know.
I won't be using this exact command because I don't need a specific function setup for this, but I didn't know about the bc command even though I've been using linux for many years. It's pretty nice. Thumbs up.