chflags

Change a file or folder's flags.

Syntax 
      chflags [-R [-H | -L | -P]] flags file ...

Options
   -R      Recurse: Change the file flags of file hierarchies rooted in the files
           instead of just the files themselves.

   -R -H   Follow symbolic links on the command line
          (by default Symbolic links within the tree are not followed.)	       

   -R -L   All symbolic links are followed.

   -R -P   No symbolic links are followed. (default)

The flags are specified as an octal number or a comma separated list of keywords.

             hidden           set the hidden flag [Hide item from GUI]

Keywords and keyword aliases - Owner or Super-user only:

             opaque           set the opaque flag 
             nodump           set the nodump flag 
             uappnd, uappend  set the user append-only flag
   uchg, uchange, uimmutable  set the user immutable flag
             uunlnk, uunlink  set the user undeletable flag

Keywords and keyword aliases - Ssuper-user only:

             arch, archived   set the archived flag
             sappnd, sappend  set the system append-only flag
   schg, schange, simmutable  set the system immutable flag
             sunlnk, sunlink  set the system undeletable flag

The immutable flag is equivalent to locking the file in the Finder's Show Info box.

Putting the letters no before an option causes the flag to be turned off.

  For example:
	     uchg    Means the file cannot be changed
	   nouchg    Means the file can be changed (immutable bit cleared)
        hidden  Will set the hidden flag
      nohidden  Will remove the hidden flag

Symbolic links do not have flags, so unless the -H or -L option is set, chflags on a symbolic link always succeeds and has no effect. The -H, -L and -P options are ignored unless the -R option is specified. In addition, these options override each other and the command's actions are
determined by the last one specified.

The sappnd and schg flags may only be unset when the system is in single-user mode. chflags(2).

Use ls -lo to see the flags of existing files.

The return status is zero if the mode is successfully changed,and >0 if an error occurs.

Examples

Lock the file or folder named "finance" against changes
$ chflags uchg finance

Make the folder ~/Library visible (this was the default setting prior to OS X Lion )
$ chflags nohidden ~/Library

Hide the folder ~/Library (Lion default)
$ chflags hidden ~/Library

Make the file MyLogs.txt append-only
$ chflags uappnd MyLogs.txt

Unlock your Documents directory and everything in it
$ chflags -R nouchg ~/Documents

“Fifteen referees. I want fifteen referees to be at this fight because there ain't no one man who can keep up with the pace I'm gonna set except me. There's not a man alive who can whup me. I'm too fast. I'm too smart. I'm too pretty. I should be a postage stamp. That's the only way I'll ever get licked” ~ Muhammad Ali

Related:

chflags man page - Apple.com
ln - Make links between files (hard links, symbolic links)
ls - List information about file(s)
setfile - Set attributes of HFS+ files