How to read only the first line of a file

I've been googling for a while, but I cannot find a function the read just first line of a file.

I need to read fi开发者_如何学Pythonrst line of a text file and extract the date from it.

new to perl.

open my $file, '<', "filename.txt"; 
my $firstLine = <$file>; 
close $file;

open THEFILE, "<filename.txt";
$first_line = <THEFILE>;
close THEFILE;

open( my $file, "x.txt");
$line = <$file>;

... a modern and popular alternative:

use Path::Tiny;
(my $firstline) = path('filename.txt')->lines( { count => 1 } );

For more info https://metacpan.org/pod/Path::Tiny#lines-lines_raw-lines_utf8

Note: since ->lines is returning a list, calling it without the brackets around $firstline it will be assigned the number of lines which have been read from filename.txt: 1 (or 0 if it's empty).