Re: How to check Inputs if Numeric

That's an FAQ actually, as you can find browsing the output of perldoc -q number:

       How do I determine whether a scalar is a number/whole/integer/f
+loat?
                                                                      
+          
       Assuming that you don't care about IEEE notations like "NaN" or
+ "Infin-
       ity", you probably just want to use a regular expression.
                                                                      
+          
          if (/\D/)            { print "has nondigits\n" }
          if (/^\d+$/)         { print "is a whole number\n" }
          if (/^-?\d+$/)       { print "is an integer\n" }
          if (/^[+-]?\d+$/)    { print "is a +/- integer\n" }
          if (/^-?\d+\.?\d*$/) { print "is a real number\n" }
          if (/^-?(?:\d+(?:\.\d*)?|\.\d+)$/) { print "is a decimal num
+ber\n" }
          if (/^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/)
                               { print "a C float\n" }
                                                                      
+          
       There are also some commonly used modules for the task.  Scalar
+::Util
       (distributed with 5.8) provides access to perl's internal funct
+ion
       "looks_like_number" for determining whether a variable looks li
+ke a
       number.  Data::Types exports functions that validate data types
+ using
       both the above and other regular expressions. Thirdly, there is
+ "Reg-
       exp::Common" which has regular expressions to match various typ
+es of
       numbers. Those three modules are available from the CPAN.
                                                                      
+          
       If you're on a POSIX system, Perl supports the "POSIX::strtod" 
+func-
       tion.  Its semantics are somewhat cumbersome, so here's a "getn
+um"
       wrapper function for more convenient access.  This function tak
+es a
       string and returns the number it found, or "undef" for input th
+at isn't
       a C float.  The "is_numeric" function is a front end to "getnum
+" if you
       just want to say, ``Is this a float?''
                                                                      
+          
           sub getnum {
               use POSIX qw(strtod);
               my $str = shift;
               $str =~ s/^\s+//;
               $str =~ s/\s+$//;
               $! = 0;
               my($num, $unparsed) = strtod($str);
               if (($str eq '') || ($unparsed != 0) || $!) {
                   return undef;
               } else {
                   return $num;
               }
           }
 
           sub is_numeric { defined getnum($_[0]) }
 
       Or you could check out the String::Scanf module on the CPAN ins
+tead.
       The POSIX module (part of the standard Perl distribution) provi
+des the
       "strtod" and "strtol" for converting strings to double and long
+s,
       respectively.
[download]

I had your same problem, too :-)

Ciao!
--bronto

The very nature of Perl to be like natural language--inconsistant and full of dwim and special cases--makes it impossible to know it all without simply memorizing the documentation (which is not complete or totally correct anyway).
--John M. Dlugosz

Comment on Re: How to check Inputs if Numeric Select or Download Code

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Re: Re: How to check Inputs if Numeric by kasmot (Novice) on Apr 01, 2004 at 03:14 UTC
Thanks to all. You guys here were really very good and of great help.. More Power..	[reply]
Re^3: How to check Inputs if Numeric by Anonymous Monk on Mar 06, 2014 at 10:29 UTC
I know this thread is old but it came up on google firstish. I searched, then came up with my own line, which I think works better than the regexp. I did not check all over, so most likely it is already around somewhere. `if ( $input+0 eq $input ){ print "it is a number!\n";}` Can someone point out the problem with this approach? Advantage for me: easy + quick, no problems with signs...	[reply] [d/l]
Re^4: How to check Inputs if Numeric by jdporter (Paladin) on Mar 07, 2014 at 02:58 UTC
Depends on whether you'd consider `"000"` a number, for example. (I would, probably, in most cases.) I reckon we are the only monastery ever to have a dungeon stuffed with 16,000 zombies.	[reply] [d/l]
Re^4: How to check Inputs if Numeric (eq 0+) by tye (Sage) on Mar 07, 2014 at 03:55 UTC
Not bad, especially given the simplicity. More potential false negatives to go with jdporter's. `for my $input (qw< +4 1.0 1e5 12345678901234567890 1.234567890123456789 >) { if( $input+0 eq $input ) { print "$input is a number!\n"; } else { print "$input is not ", 0+$input, "\n"; } } __END__ +4 is not 4 1.0 is not 1 1e5 is not 100000 12345678901234567890 is not 1.23456789012346e+019 1.234567890123456789 is not 1.23456789012346` [download] Update: It successfully detects if $input is (primarily) holding a numeric value (an IV or NV, how Perl stores an integer and floating point, respectively) or is holding a string value that equals the canonical string representation of any possible Perl numeric value. So I don't believe that there are any false positives. The false negatives are the many ways to reasonably represent a numeric value that aren't Perl's canonical representation. - tye	[reply] [d/l]
Re^4: How to check Inputs if Numeric by Anonymous Monk on Mar 16, 2014 at 11:52 UTC
just a quick (final) note : ($nr+0 eq $nr ) is not perfect for checking on numbers in general, but it is a very good check for integer numbers. It avoids perl complaining about casting as some other methods would and is pretty easy on resources	[reply]
Re^4: How to check Inputs if Numeric by choroba (Cardinal) on Mar 16, 2014 at 16:11 UTC
If you don't mind "nan" and "inf" among numbers... لսႽ† ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ	[reply]
Re^4: How to check Inputs if Numeric by Anonymous Monk on Mar 08, 2014 at 20:00 UTC
thanks for the replies! some of the problems pointed out would not bother me much IRL ( i.e. most of my applications ), the one with 1.0 for example would. Back to regexp's I suppose :/	[reply]