A cli calculator that recognizes wrong math syntax?

Question

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?

Answer 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)

Answer 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
>>