How does Perforce ignore file syntax differ from gitignore syntax?

I had a similar question and then found this article where I learned that Perforce does accept .gitignore files.

In fact, you can specify more than one filename in P4IGNORE. In reality, my P4IGNORE looks like this (this is a new feature in 2015.2):

P4IGNORE=$home/.p4ignore;.gitignore;.p4ignore;

In addition to the two you listed I've seen that wildcards won't match against directories, only files.

Also, as far as I can tell (the P4IGNORE mechanism is incompletely documented):

P4IGNORE seems to have no way to escape # (the hash sign, a character that I really want to have in P4IGNORE since EMACS creates backup files named #filename#.

It looks like # in P4IGNORE is a comment character, but only if the first character on a line.

So

*#*

seems to ignore all files with # in them.i.e. it seems to be the equivalent of Perl regexp qr{^.#.$}.

This is a bit scary, since if # was the normal comment character in most systems, the pattern # would be a * followed by a comment #*, and would ignore all files. But it seems to work.

(Git's handling of # is a bit special as well.)

P4IGNORE does not seem to handle patterns such as

# matches any single character filename    ?

a single character

[seq] 

matches any character in set

etc.,

so to ignore a filename with a single letter like 'a', I had to list all 62 possibilities [a-zA-Z0-9]. (I have a habit of creating tmp files like 'a', 'b' ...).

I have not yet grokked Perforce's handling of periods in filenames.
I know for sure that to ignore a filename like '.#more-crap'you have to do

.#*

in addition to

*#*

but this may just be normal dot file hiding.

However, there have been several cases where a pattern like

tmp-*

was not catching 'tmp-foo.txt'

that I fixed by adding

tmp-*.*

(Note: most recently I have been using bzr and hg, with fully powerful regexps, so may be looking for stuff more powerful than git provides)