how to perform a basic arithmetics from unix csh/tcsh shell

Question

Under windows, when I need to perform a basic calculations, I use a built-in calculator. Now I would like to find out what is the common way if you only have a shell.

Thanks

Answer 1

You can use dc. Or bc.

Answer 2

Bash supports basic (integer only) arithmetic inside $(( )):

$ echo $(( 100 / 3 ))
33
$ myvar="56"
$ echo $(( $myvar + 12 ))
68
$ echo $(( $myvar - $myvar ))
0
$ myvar=$(( $myvar + 1 ))
$ echo $myvar
57

(example copied straight from the IBM link)

• More in-depth discussion of bash arithmetic

Answer 3

If you're using bash, here's a handy example of a small shell script that allows you to do calculations from the command line (including specifying precision for floating-point numbers):

http://www.novell.com/coolsolutions/tools/17043.html

Answer 4

And you can always use the python interpreter, it's normally included in linux distros.

http://docs.python.org/tutorial/introduction.html#using-python-as-a-calculator

$ python
Python 2.6.2 (r262:71605, Apr 14 2009, 22:40:02) [MSC v.1500 32 bit (Intel)]
Type "help", "copyright", "credits" or "license" for more information.
>>> 2+2
4
>>> # This is a comment
... 2+2
4
>>> 2+2  # and a comment on the same line as code
4
>>> (50-5*6)/4
5
>>> # Integer division returns the floor:
... 7/3
2
>>> 7/-3
-3
>>> # use float to get floating point results.
>>> 7/3.0
2.3333333333333335

The equal sign ('=') is used to assign a value to a variable. Afterwards, no result is displayed before the next interactive prompt:

>>> width = 20
>>> height = 5*9
>>> width * height
900

And of course there's the math module which should solve most of your calculator needs.

>>> import math
>>> math.pi
3.1415926535897931
>>> math.e
2.7182818284590451
>>> math.cos() # cosine
>>> math.sqrt()
>>> math.log()
>>> math.log10()

Answer 5

I know this is technically not arithmetic from the shell, but most modern distributions come with ruby and IRB (interactive ruby shell) which is perfect for this sort of thing (assuming you know a bit of Ruby). Another alternative is invoking the python interpreter which starts in an interactive shell if you don't provide any arguments.

Answer 6

From this web page (for csh and derivatives, since you asked):

% @ x = (354 - 128 + 52 * 5 / 3)
% echo Result is $x
Result is 174

and

% set y = (354 - 128 + 52 / 3)
% echo Result is $y
Result is 354 - 128 + 52 / 3

notice the different results.

Personally, I stick to /bin/sh and call awk or something (for maximal portability), or others have exhibited the bash approach.

Answer 7

There are many good solutions given here, but the 'classic' way to do arithmetic in the shell is with expr.

Answer 8

You can also use Perl easily where bc or expr are not powerful enough:

$ perl5.8 -e '$a=1+2; print "$a\n"' 
3

Answer 9

Alternative option is to use the built in BC command