What does "\z" mean in Perl?

Some people use the flags /xms as the default starting point for every regex. If you do that, then:

\A  \z   --beginning and end of the entire string
^   $    --beginning and end of a "line" within the string

Then just forget about \Z, which is unnecessary.

use strict;
use warnings;
use 5.010;

my $string = "HELLO\nWORLD\nGOODBYE";


my @patterns = (
    '\A (.)',       #Match start of entire string followed by any char
    '^ (.)',        #Match start of every line followed by any char
    
    '(.) \z',     #Match any char followed by end of the entire string
    '(.) $',      #Match any char followed by end of a line
);

for my $pattern (@patterns) {
    my @matches =  $string =~ /$pattern/gxms;
    say "@matches";

    say '*' x 20;
}


--output:--
H
********************
H W G
********************
E
********************
O D E
********************
[download]

I remember grep only takes two input variables, one is the expression and the other one is an array.

Actually,

grep BLOCK LIST

A list is a series of comma separated values, e.g. 1, 'a', 2, 'b'. So if you give perl an array along with a scalar value in a spot where perl expects a list, then perl extracts the values from the array and adds the scalar value to the end, creating one list.

That phenomena happens in a lot of places in perl. As hippo explained, look what happens if you call a sub with two arrays:

use strict;
use warnings;
use 5.010;

sub do_stuff {
    my @x = shift;
    my @y = shift;

    say "@x";
    say "@y";
}

my @arr1 = (10, 20);
my @arr2 = ('a', 'b');

do_stuff(@arr1, @arr2);
[download]

What do you expect the output to be?

When you call the function perl 'unwinds' the first array into a list of comma separated values, and perl does the same with the second array, creating one big list--as if you called the function like this:

do_stuff(10, 20, 'a', 'b');
[download]

That list then gets assigned to the array named @_. So when you shift one value from @_ and assign the value to the array @x, it's as if you wrote:

my @x = 10;
[download]

And in that line, because there is an array on the left, which expects a list on the right, perl converts the scalar 10 to the list (10) giving you this:

my @x = (10);
[download]

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