Command-Line math

I'm trying to come up with a Perl script that will allow me to type in a command-line math expression, push enter, and have the expression's evaluation printed in the terminal. Here's a simple example:

#!/usr/bin/perl print 'Enter expression:n'; $a = <STDIN>; $a =~ s/n//g; print ($a); print 'n';

The file is called 'm', it's been chmod to 755, and placed in my path. So if I type 'm' at the terminal, and enter 1+2, the string '1+2' is returned instead of the integer '3'.

This might be more of a Perl than a Linux/bash question, but how do I get the variable $a to be viewed as a math expression rather than a string?

Thanks, and best regards,

You could also do this from the shell:

perl -e 'print 1+2'

I'm sorry that I can't help you with Perl, but here's a Bash version:

echo -n 'Enter expression: ' read expr echo $(($expr))

So is awk, when

calc () { echo $* bc -l }

will give you a real calculator. For that matter,

echo $expr bc -l

is pretty easy without being a Bash function.

Thanks, Tony. Works like a charm!

All the best,

Perhaps, but I'm introducing some high-school kids to (rudimentary) Linux and Perl, and I'd like to give them a quick way to try out the logic/syntax of their math before they 'paste' it into a Perl template. The Perl they'd be doing is only the math, and just enough to crunch a few lab-collected numbers and to get an idea of how computers are used other than for web, video, and music.

Best regards, And thanks for the feedback,

Yeah, Bill Gates making it an artform.

All the way up to when they want to change a system script.

Provide them with all the tools and let them pick the best tool to the job.

Now you are being ignorant.

Awk, for instance, is clearly an extremely good and easy to use language which is in many cases superior to perl for handling structured text. And, as such, should be used when it is suitable. The same applies to shell programming and sed.

Agreed...to a point. These are high school kids in a physics class, so introducing them to Linux/Perl is a perk that's being fitted into a tight time frame. It there's just one scripting language they get exposed to, I've guessed that Perl is probably the one it should be...mostly because it's the one that I know most about...but also because it's more than just for scripting.

With that said, I've always believed that one should never get so comfortable with what's in front of them that they become fearful of learning something new. I use Mac's, Windows and Linux, and enjoy having the strengths of all three at my disposal. Ditto with programming languages, although I'm at best an amateur programmer, so you're more informed to address that topic than I am.

With all that said, here's question that a little Bash would certainly be of use to answer:

3*2

6

Is there a way to get the Bash variable $N to be recognized in the Perl just like $a is seen as a math expression?

Best regards,

Nope, you might not have perl available on many *nix systems, awk/sed/ksh are extremely powerfull tools and for sure available.

Don't get me wrong, I'm using perl myself and it's great for .cgi, but it won't help you much if it's not on the system and for some reasons, not allowed to install.

Michael Heiming

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Some shells allow perl to get some 'env' vars, but that's all.

Michael Heiming