Meaning of <=> (less than, equal, greater than) in Perl?

perl comparison operators comparison-operators
jtpereyda picture jtpereyda · Oct 22, 2011 · Viewed 10.1k times · Source

In this answer, I saw the syntax <=>; what does this mean? It seems to be some sort of comparison based on the context, but that's all I can gather. Partial context:

sub rev_by_date { $b->[9] <=> $a->[9] }
my @sorted_files = sort rev_by_date @files;

Answer

bhamby picture bhamby · Oct 22, 2011

From Perldoc:

Binary "<=>" returns -1, 0, or 1 depending on whether the left argument is numerically less than, equal to, or greater than the right argument. If your platform supports NaNs (not-a-numbers) as numeric values, using them with "<=>" returns undef. NaN is not "<", "==", ">", "<=" or ">=" anything (even NaN), so those 5 return false. NaN != NaN returns true, as does NaN != anything else. If your platform doesn't support NaNs then NaN is just a string with numeric value 0.

Related questions

How can I check if a Perl array contains a particular value?

I am trying to figure out a way of checking for the existence of a value in an array without iterating through the array. I am reading a file for a parameter. I have a long list of parameters I …

Read More
What is the proper way to check if a string is empty in Perl?

I've just been using this code to check if a string is empty: if ($str == "") { // ... } And also the same with the not equals operator... if ($str != "") { // ... } This seems to work (I think), but I'm not sure it's the correct way, …

Read More
Is there any use for Bash scripting anymore?

I just finished my second year as a university CS student, so my "real-world" knowledge is lacking. I learned Java my first year, continued with Java and picked up C and simple Bash scripting my second. This summer I'm trying …

Read More