So what exactly does <FILE> do?

Question

So, I've used <FILE> a large number of times. A simple example would be:

open (FILE, '<', "someFile.txt");
while (my $line = <FILE>){
print $line;
} 

So, I had thought that using <FILE> would take a a part of a file at a time (a line specifically) and use it, and when it was called on again, it would go to the next line. And indeed, whenever I set <FILE> to a scalar, that's exactly what it would do. But, when I told the computer a line like this one:

print <FILE>;

it printed the entire file, newlines and all. So my question is, what does the computer think when it's passed <FILE>, exactly?

Answer 1

Diamond operator <> used to read from file is actually built-in readline function.

From perldoc -f readline

Reads from the filehandle whose typeglob is contained in EXPR (or from *ARGV if EXPR is not provided). In scalar context, each call reads and returns the next line until end-of-file is reached, whereupon the subsequent call returns undef. In list context, reads until end-of-file is reached and returns a list of lines.

If you would like to check particular context in perl,

sub context { return wantarray ? "LIST" : "SCALAR" }

print my $line  = context(), "\n";
print my @array = context(), "\n";
print context(), "\n";

output

SCALAR
LIST
LIST