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Javier López
Asked: 2015-11-03 23:11:37 +0800 CST

A cli calculator that recognizes wrong math syntax?

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I'm looking for a way to do quick calculations in the terminal (using utilities available in Ubuntu minimal) and get accurate fail errors when the math syntax is incorrect, eg: cli-calculator "foo+bar" || echo invalid math syntax

Some of the inputs would be:

  • 1+1 #should print 2 and return a 0 code

  • 5/2 #should print 2.5 and return a 0 code

  • 1/0 #should return a non 0 code

  • foo+bar #should return a non 0 code

I've tried bc, shell integrated arithmetic, expr, awk, perl and python but so far none has satisfied fully my requirements, so I'm looking for alternatives, follow use cases:

  • bc, it's able to do operations with float numbers but doesn't return error codes on invalid syntax input

    $ echo "1/0" | bc -l && echo all is fine || echo math syntax error
Runtime error (func=(main), adr=3): Divide by zero
all is fine
$ echo "foo+bar" | bc -l && echo all is fine || echo math syntax error
0 #should return an error
all is fine

  • Shell integrated arithmetic and expr, don't support operations with float numbers and return valid codes on invalid math input

    $ echo $((5/2))
2 #should return 2.5
$ echo $((foo+bar))
0 #should return an error
$ expr 5 / 2
2 #should return 2.5
$ expr foo+bar
foo+bar #should return an error

  • awk|perl, don't return invalid status codes on invalid math input.

    $ awk "BEGIN {print foo+bar; exit}"
0 #should return a non 0 number and probably output an error
$ echo "foo+bar" | perl -ple '$_=eval'
0 #should return a non 0 number and probably output an error

  • python, supports float arithmetic operations and return status errors on invalid math syntax but it's slow.

    $ python -c 'from __future__ import division; from math import *; print(foo+bar)' && echo all fine || echo math syntax error
NameError: name 'foo' is not defined
math syntax error #good!
$ python -c 'from __future__ import division; from math import *; print(5/2)' && echo all fine || echo math syntax error
2.5` #good!
all fine

Any ideas?

command-line

2 Answers

  1. What about calc

    sudo apt-get install apcalc

    Examples

    % calc 1/0  
    Error 10001

% calc foo + bar
"foo" is undefined
Error in commands

% calc 5/2
    2.5

    Or qalc

    % qalc 1/0
error: Division by zero.
1 / 0 = 1 / 0

% qalc foo + bar
error: "foo" is not a valid variable/function/unit.
0 + bar = 1 bar

% qalc 5/2      
5 / 2 = 2.5

    bc

    echo "1/0" | bc  
Runtime error (func=(main), adr=3): Divide by zero

echo "scale=1; 5/2" | bc
2.5

    And this is correct, 0 + 0 is 0

    % echo "foo+bar" | bc
0

    Or gcalccmd, the console version of gnome-calculator the calculator of the GNOME desktop environment.

    Examples

    % gcalccmd    
> 1/0
Error (null)
> foo + bar
Error 3
> 5/2
2,5

    Note that gcalccmd does not have readline support, so only the most basic line editing features are available. (Backspace works, but left/right keys don't)

    • 3

  2. Octave is another alternative. It is a very powerful free tool with a syntax 'like the commercial tool matlab'. If you want to run it without a gui, use the option --no-gui or the command octave-cli.

    sudo apt-get install octave octave-info

    Example based on your 'valid and invalid' expressions:

    $ octave --no-gui
GNU Octave, version 4.0.0
Copyright (C) 2015 John W. Eaton and others.
This is free software; see the source code for copying conditions.
There is ABSOLUTELY NO WARRANTY; not even for MERCHANTABILITY or
FITNESS FOR A PARTICULAR PURPOSE.  For details, type 'warranty'.

Octave was configured for "i686-pc-linux-gnu".

Additional information about Octave is available at http://www.octave.org.

Please contribute if you find this software useful.
For more information, visit http://www.octave.org/get-involved.html

Read http://www.octave.org/bugs.html to learn how to submit bug reports.
For information about changes from previous versions, type 'news'.

>> 1+1 #valid
ans =  2
>> 5/2 #valid
ans =  2.5000
>> 1/0 #invalid
warning: division by zero
ans = Inf
>> foo+bar #invalid
error: 'foo' undefined near line 1 column 1
>> foo=1;bar=2  # assign values to foo and bar
bar =  2
>> foo+bar #now valid
ans =  3
>>
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