#!/usr/bin/perl
use strict;
use warnings;
use 5.014;
# juliosergio's test.pl

print "Enter a number or string: ";
my $s = <STDIN>;
chomp $s;
if ( $s =~ /^[0-9,.E]+$/ ) {      # char class, 1 or more of any of those specified
  say "$s is a number\n";         # & the ^...$ restricts what's tested.
} else {
  say "'$s' may be a string\n";    # Not "isn't a number"
}

##</code><code>##

C:\>numVSstring.pl
Enter a number or string: 123.2
123.2 is a number

C:\>numVSstring.pl
Enter a number or string: 1E3
1E3 is a number

C:\>numVSstring.pl
Enter a number or string: 17
17 is a number

C:\>numVSstring.pl
Enter a number or string: now is the time
'now is the time' may be a string

C:\>numVSstring.pl
Enter a number or string: III
'III' may be a string