Comments on: Simple Maths in the Unix Shell

By: Commandes Unix « Francesco’s FAQ

Commandes Unix « Francesco’s FAQ — Tue, 26 May 2009 13:30:55 +0000

[...] -pour faire des math dans une shell : ici [...]

By: unixshell

unixshell — Mon, 26 Jan 2009 17:04:46 +0000

That works with Bash (possibly ksh too, can’t remember off the top of my head) but it doesn’t work with the original Bourne shell, nor with dash (which looks likely to replace bash as the default root shell in many upcoming Linux distro’s).

Using bash-specific stuff is fine, if we are sure of having bash installed; if not, then we need to be more generic in our approach

By: ddouthitt

ddouthitt — Mon, 26 Jan 2009 16:20:42 +0000

I’m surprised no one mentioned the real solution to shell math. Using the above example:

a=1
b=2
c=3
d=$(( $a + $b $c ))
echo “$d”

unlike expr, dc, and bc, this requires nothing more than the shell, and requires no exec calls (and no binaries to be read in from disk).

By: unixshell

unixshell — Mon, 03 Sep 2007 13:37:42 +0000

We dont’ use set in Bourne, so replace that line with this:

d=`expr $a + $b + $c`

Should work fine.

By: muralee

muralee — Mon, 03 Sep 2007 12:40:11 +0000

why the below code does not work

a=1
b=2
c=3
set d=`expr [[$a + $b] + $c ]`
echo “$d”

what is the fix req.

By: More maths stuff - bc in detail « *nix Shell

More maths stuff - bc in detail « *nix Shell — Sun, 08 Apr 2007 00:22:36 +0000

[...] There’s a great post about bc at basicallytech.com – I think that I’ve already covered most of the same ground, but it’s got lots of great [...]

By: unixshell

unixshell — Mon, 26 Mar 2007 23:26:34 +0000

Updating again… I’ve done another, related post, here: http://nixshell.wordpress.com/2007/03/26/calculating-averages/

It deals specifically with averages, but there is more detail about bc, also.

By: Calculating Averages « *nix Shell

Calculating Averages « *nix Shell — Mon, 26 Mar 2007 22:30:42 +0000

[...] The Simple Maths post seems to be the most popular article in the so-far short life of this [...]

By: unixshell

unixshell — Tue, 30 Jan 2007 01:19:48 +0000

bc is indeed far more powerful than expr. Both are rather awkward, though, with their own quirks. I guess if I’m that upset, I should fix it instead of griping about it. It’s been over a decade since I studied Finite State Machines (FSMs) and the like, so I’m probably not the person to provide the ultra-powerful shell-maths tool. There is certainly a need for one, so any students out there looking for a PhD thesis… this could be an idea!

By: Constantin

Constantin — Mon, 29 Jan 2007 14:20:27 +0000

bc is great because it supports long numbers (as long as you want) and arbitrary precision (set with scale=100 e.g. for 100 decimal places). It can also do trigonometric math and other stuff, if you load it with the math library (bc -l). But I didn’t know how to use it non-interactively / from shell scripts. Thanks!