Perl compare operators and stringified "numbers"

Question

I've been working a lot lately with perl, still I dont really know how <,>,>=,=<, ne,gt, etc.. on stringified "numbers", by "number" I mean something like: '1.4.5.6.7.8.0'

correct me If I'm wrong, the following returns true:

if ('1.4.5' > '8.7.8');

because both will be coerced to true (not an empty string). but, how does ne,gt,etc string operators work on such numbers?

basically I'm trying to compare version numbers consisted of the following form:

1.3.4.0.2

I can make a numerical comparison of each digit, but before, I ranther want to know of the string comparing operators perform on such strings.

Thanks,

Answer 1

First: Please use warnings all the time. You would have realized the following at once:

$ perl -wle 'print 1 unless "1.4.5" > "8.7.8"'
Argument "8.7.8" isn't numeric in numeric gt (>) at -e line 1.
Argument "1.4.5" isn't numeric in numeric gt (>) at -e line 1.

Perl v5.9.0 came distributed with version. And this module makes it very easy to compare version numbers:

use warnings;
use version;

my ($small, $large) =  (version->parse('1.4.5'), version->parse('8.7.8'));

print "larger\n"    if $small > $large;
print "smaller\n"   if $small < $large;

Answer 2

A string comparison will only work if every number between the dots has the same length. A string comparison has no knowledge of number and will begin to compare dots and digits (as they are both characters in a string).

There a CPAN module that does exactly what you are looking for: Sort::Versions

Answer 3

When you compare strings using numerical relation operators <, >, etc., Perl issues a warning if you use warnings. However, Perl will still attempt to convert the strings into numbers. If the string starts with digits, Perl will use these, otherwise the string equates to 0. In your example comparing '1.4.5' and '8.7.8' has the same effect as comparing numbers 1.4 and 8.7.

But for ne, gt, etc. it really doesn't matter if your strings consist of numbers or anything else (including dots). Therefore:

print "greater" if '2.3.4' gt '10.1.2'  # prints 'greater' because '2' > '1' stringwise 
print "greater" if '02.3.4' gt '10.1.2' # prints nothing because '0' < '1' stringwise

Therefore you cannot use neither >, <, etc. nor gt, lt, etc. for version comparison, you have to choose different approach, as proposed in another answers, for example.