I've been playing around with this bit, but can't quite seem to get the last part right.

$checkit = "tony!|bob&sue|me@me.com";

$checkit =~ tr/[A-Za-z0-9][ ][.][|]/\*/c;

I've got it matching all non-character, non-numeric (except for space, period and pipe).

I want to replace the non-items with a backslash and the non-item. (tony\!|bob\&sue|me\@me.com).

I can't seem to figure out what to use where the * is in the tr// bit. I tried $1 (and about 6 million other things) but that didn't work.

Any suggestions?

You probably want a substitution for that.

Is this what you need?

Yep. That's it. It works.

I was (am) also confused by the ^ character apparently it can be used as "not" and it can be used as "starts with". Correct me if I'm wrong.

Okay, here's my take on what is happening with s///g:

$checkit =~ s/([^\w\s.|])/\\$1/g;

s/ = substitue
([ ]) = a range of items
^ = that is not
\w = any alpha-numeric character A-Z, 0-9
\s = or whitespace (spaces for the most part)
. = or period
| = or pipe
/ = with
\\ = a backslash
$1 = and the item being replaced
/g = and do it (globally) for each occurance you find.

Yep you are correct.

^ will match the beginning of a string if used like so:

$string =~ /^something/;

...or the beginning of a line in a multi-line string, if you use /m, eg:

$string =~ /^abc/m;

[^ ...] however is a negated character class. Meaning anything *other* than what you specify, will be matched.