When posting code, you need to wrap it in <code> tags so it doesn't get mangled - see Markup in the Monastery.

Command line switches are documented in perlrun. The switches -w, -Mstrict, -l, and -e enable warnings, strict, automatic chomps and one-liner execution respectively.

When you have questions about regular expressions, the go-to sources are perlre and perlretut. In this case, Assertions in perlre says

\z  Match only at end of string

and Modifiers in perlre says:

m

Treat string as multiple lines. That is, change "^" and "$"
from matching the start or end of the string to matching 
the start or end of any line anywhere within the string.

s

Treat string as single line. That is, change "." to match 
any character whatsoever, even a newline, which normally it 
would not match.

Used together, as /ms, they let the "." match any character 
whatsoever, while still allowing "^" and "$" to match, 
respectively, just after and just before newlines within 
the string.

x

Extend your pattern's legibility by permitting whitespace 
and comments. Details in /x
[download]

See also /x.