7.3.1. Problem

7.3.2. Solution

open(FH, glob("~joebob/somefile")) || die "Couldn't open file: $!";

$filename =~ s{ ^ ~ ( [^/]* ) }
              { $1
                    ? (getpwnam($1))[7]
                    : ( $ENV{HOME} || $ENV{LOGDIR}
                         || (getpwuid($<))[7]
                       )
}ex;

7.3.3. Discussion

    ~              # current user's home directory
    ~/blah         # file blah in current user's home directory
    ~user          # a particular user's home directory
    ~user/blah     # file blah in a particular user's home directory

open(MAILRC, "<", "~/.mailrc")           # WRONG: tilde is a shell thing
    or die "can't open ~/.mailrc: $!";

open(MAILRC, "<", glob("~/.mailrc"))     # so expand tilde first
    or die "can't open ~/.mailrc: $!";

The alternative solution, the substitution, uses /e to evaluate the replacement as Perl code. If a username follows the tilde, it's stored in $1, which getpwnam uses to extract the user's home directory out of the return list. This directory becomes the replacement string. If the tilde was not followed by a username, substitute in either the current HOME environment variable or the LOGDIR one. If neither of those is valid, look up the effective user ID's home directory.

You could spell glob('~gnat') as <~gnat>, but that would look too much like a read from a filehandle, so don't do that.

7.3.4. See Also