UNIX for Dummies Questions & Answers

Hi all

I am trying to figure out how to specify integers and floating points specifically in a Perl program.

Basically the idea is that I want the user to input an integer and then dependent on that value they get a specific output. Now my problem is that I don't know how to write the content of the parentheses of either of the two following commands:

if ( input != integer ) or
if ( input = floating point )

I basically have the rest of the program down but haven't been able to figure this small part out.
How do I tell Perl that if the user inputs a floating point number then it should print an error message?

Any ideas?

Consider the input as a string. You could strip out all characters [0-9] and if there's anything left over, they've entered something they shouldn't have.

Hey again

I tried looking up stripping both in the Perl manual and on Google, but didn't really understand how to use that information.

I found something like this:

Code:

for ($string) {
        s/^\s+//;                     I am guessing this means before
        s/\s+$//;                     and this after, but what is the ^ for?
    }

for removing spaces before and after the string.
My problem is that I can't find any information about what the different parts mean.
I am wondering if in my case I can use something like this:

Code:

for ($string) {
        s/0\s//;
        s/1\s//;
    }

and fill it out for 2-9 too or maybe make a loop inside the for loop to take the 10 numbers by turn.
And then afterwards use: if ($string = "" ) : continue program, else : error message.

Ah, you're totally new to perl?

Code:

if( $val =~ /^\d+$/ )
{
  # Is a decimal
}
else
{
  # Is a float or other invalid input
}

Oki cool thanx.

It worked as intended.
But now I'm going to be really annoying since, yes I'm a total newbie. But I like to understand what the code I use actually does, since then it's a lot easier to rewrite to something else later.

if( $val =~ /^\d+$/ )

What does the ~ /.../ part mean?
The ^ should be the beginning of the string
and the $ should be the end of the string
and \d+ represents any integer/decimal in the string.

It means "here be a regular expression". That's one of the defining features of Perl.
Right, and right.
It means "at least one decimal (0-9)", no punctuations, letters, or other cruft.

=~ is the regular expression operator. A regular expression can do lots of different things, but is often just used to compare. The syntax of the regex is kind of similar to sed's but with significant differences too.