Expanding Tildes in Filenames

Problem

You want to open filenames like ~username/blah, but open doesn't interpret the tilde to mean a home directory.

Solution

Expand the filename manually with a substitution:

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

Discussion

The uses of tilde that we want to catch are:

 ~user ~user/blah ~ ~/blah

If no name follows the ~, the current user's home directory is used.

This 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 environment variables is valid, look up the effective user ID's home directory.