how do i remove \ (backslash) from file names

how do i remove \ (backslash) from file names when i copying from tag as it will turn it into folders

You can keep the mask to create the filename. Only you have to treat it again.
So instead of only entering (example):
%track% - %artist% - %title%
append the following:
$replace($validate(%track% - %artist% - %title%),'','_')
This will replace any backslash with an underscore.

Just released $validate doesn't work with \

Is this a known bug?

I fell into the same trap as I thought that the backslash would be replaced.
But as the backslash is a valid character for a fully qualified filename it is ignored by the $validate() function.
The help categorizes /?*"<>|: as illegal.

I would say the function could work for both.
For a filename remove all:
\ /?*"<>|:

And for filepaths remove just:
/?*"<>|:

Just the function coded differently under the hood. Least now I know this is the case. Thanks.

Note: The colon is allowed for filepath, at the position right beside the drive letter.

See also ...
[F] $validate() broken?

DD.20140830.2040.CEST

Well instead of:

Remove:
/?*"<>|

so what do I need to put in my actions



$replace($validate($num(%track%,2) %title%),'','_')

$replace($validate($num(%TRACK%,2)' '%TITLE%,'_'),'\','_')

Note: The picture from 'fatmanpeters' does not show backslash in the TITLE column, but slash.

DD.20140902.1130.CEST

True.
Yet, the question was about the backslash. Let's see what the OP tells us.
Anyway: the slash (no "back") gets treated by the $validate() function. The backslash does not.