There are a number of methods used to hide files in the Finder.app and from the end user in Mac OS X. I would only suggest using two: Unix style "preceding dot" naming system and setting the invisible attribute in the file's meta information.

The Unix method is very easy and survives cross-platform migration but isn?t nearly as neat or functional for the GUI as the meta attribute method. Plus I'm an Apple slut so I wanted to know how the meta solution worked.

Unix style

The Unix style of hiding files from general browsing is to begin the file or directory name with a period (E.g. .htaccess or .bash_profile). This will, by default, hide the file or directory from the Finder.app AND the ls list command (unless the -a flag is passed) on most if not all *nix systems.

This is useful for files and directories that are not normally accessed by either GUI uses in the Finder.app or from command-line uses. The .bash_profile file contains environmental setting for a System-user that does not need to be touched often but does need to be contained in the home directory for the user. These files can be viewed on the command-line as well as in the Find.app but the default setting need to be altered to allow this Viewing the files on the command-line is allowed by using the -a flag via the command-line:

$ ls
Desktop			Library			Pictures
Documents		Movies			Public
Downloads		Music			Sites

$ ls -a
.			.dvdcss			Documents		Pictures
..			.python-eggs		Downloads		Public
.DS_Store		.ssh			Library			Sites
.Trash			.viminfo		Movies
.bash_profile		Desktop			Music

Viewing 'dot' files in the Finder.app requires the preference file for the Finder.app to be altered and Finder.app to be relaunched. This can be accomplished by the following commands:

# SHOW 'dot' files in Finder.app
$ defaults write com.apple.Finder AppleShowAllFiles YES
$ killall Finder

# HIDE 'dot' files in Finder.app
$ defaults write com.apple.Finder AppleShowAllFiles NO
$ killall Finder

SetFile meta information

The more interesting and Mac-centric approach is to set the invisibility attribute for the meta of the file. This is how much of the BSD underbelly of Mac OS X is now hidden from the GUI users but without requiring a major rewrite and thereby causing incompatibility of the Unix arm of the system to other *nix systems and applications.

An example of some standard directories are /etc, /var, and /usr. These are directories found on every *nix system but hidden from the Finder.app because they would only cause confusion and most-likely, deletion by users not 'in the know'. The tool need for setting attributes of files and directories is part of Apple's Developer tools and located here: /Developer/Tools/SetFile.

Directories (folders) can be set as invisible by using the correct options for SetFile:

# Show '/private' in the Finder.app
$ sudo SetFile -a "v" /private

# Hide '/private' from the Finder.app
$ sudo SetFile -a "V" /private

SETFILE(1)                BSD General Commands Manual               SETFILE(1)

NAME
     /usr/bin/SetFile -- set attributes of files and directories

SYNOPSIS
     /usr/bin/SetFile [-P] [-a attributes] [-c creator] [-d date] [-m date]
                      [-t type] file ...

DESCRIPTION
     /usr/bin/SetFile is a tool to set the file attributes on files in an HFS+
     directory. It attempts to be similar to the setfile command in MPW. It
     can apply rules to more than one file with the options applying to all
     files listed.

     Flags:

     -P  Acts on a symlink file instead on the file the symlink resolves to.

     -a attributes  Sets the file attributes bits where attributes is a string
                    of case sensitive letters. Each letter corresponds to a
                    file attribute: an uppercase letter indicates that the
                    attribute bit is set (1), a lowercase letter indicates
                    that it is not (0).  Note: attributes not specified remain
                    unchanged.

                    A | a    Alias file

                    B | b    Has bundle

                    C | c    Custom icon (allowed on folders)

                    D | d    Located on the desktop (allowed on folders)

                    E | e    Extension is hidden (allowed on folders)

                    I | i    Inited - Finder is aware of this file and has
                             given it a location in a window. (allowed on
                             folders)

                    L | l    Locked

                    M | m    Shared (can run multiple times)

                    N | n    File has no INIT resource

                    S | s    System file (name locked)

                    T | t    "Stationery Pad" file

                    V | v    Invisible (allowed on folders)

                    Z | z    Busy (allowed on folders)

     -c creator     Specifies the file's creator, where creator can be a
                    string of four MacRoman characters, an empty string ('')
                    designating a null creator, or a binary, decimal, octal,
                    or hexadecimal number in standard notation (e.g.
                    0x52486368).

     -d date        Sets the creation date, where date is a string of the
                    form: "mm/dd/[yy]yy [hh:mm:[:ss] [AM | PM]]" Notes:
                    Enclose the string in quotation marks if it contains spa-
                    ces. The date must be in the Unix epoch, that is, between
                    1/1/1970 and 1/18/2038. If the year is provided as a two-
                    digit year, it is assumed to be in the 21st century and
                    must be from 00 (2000) through 38 (2038).

     -m date        Sets the modification date where date is a string of the
                    form in -d above. (mm/dd/[yy]yy [hh:mm:[:ss] [AM | PM]])

     -t type        Sets the file type, where type can be a string of four
                    MacRoman characters, an empty string ('') designating a
                    null type, or a binary, decimal, octal, or hexadecimal
                    number in standard notation (e.g. 0x55455955).

RETURN VALUES
     0        attributes set
     1        syntax error
     2        any other error

SEE ALSO
     GetFileInfo(1)

EXAMPLES
     This command line sets the modification date of "myFile":

     SetFile -m "8/4/2001 16:13" myFile

Mac OS X                        January 4, 2009                       Mac OS X