问自制软件不会将gcc 5.3链接到/usr/local/bin/gcc (OS X 10.11.4 El Capitan)

EN

    #!/usr/bin/perl
    # relink_gcc unlinks the old gcc and links the current version
    #
    # SYNOPSIS:
    #   cd /usr/local/bin
    #   relink_gcc
    #
    # DESCRIPTION:
    #   Homebrew installs gcc version N.X as gcc-N. All other components
    #   of the Gnu Compiler Collection are installed with the '-N' suffix.
    #   E.g. g++-N, c++-N, ... However, I prefer to have the names w/o
    #   the '-N' suffix so I can use the same Makefiles on different
    #   computers.  This program changes the links from the plain gcc
    #   (and its family) to point to the most recent gcc version.
    #   Because 'darwin' also changes version, the program changes the
    #   version of programs with 'darwin' in their names to the current
    #   version. The gcc and darwin versions are currently hardcoded.
    #
    # CAVEAT:
    #   Make a backup of /usr/local/bin and /usr/local/Cellar before
    #   using this script
    
    use strict;
    use warnings;
    
    # Set parameters here. I might add command line args at some point.
    #..Dry run only prints what would be done. Does not actually do it.
    my $dryrun = 1;

    my $new_version = 10; 
    my $ending = "-$new_version";
    my $re_ending = qr/$ending/;
    
    # ..In case upgrading one sub-version to another (e.g. 5.2.0 to 5.3.1)
    #   (moot if upgrading to new version (e.g. 5.N.M to 6.K.L)
    my $old_sub = qr/5\.2\.0/;
    my $new_sub = qr/$new_version\.2\.0/;
    # ..To find the Darwin version, at the command line prompt enter
    #       uname -r
    my $new_darwin_version = "17.7.0";
    
    
    
    # No changes needed below this line (I hope)
    
    my @gcc_N_list = glob qq("*${ending}");
    
    print "found $#gcc_N_list files ending in '$ending'\n";
# ..If the file exists but is not a link, leave it alone.
    if (-e $plain && (! -l $plain )){ 
        print "$plain is not a link\n";
        next;
    }   
# ..File pointed to by '$file'
    my $orig = readlink($file);
    if ($dryrun) {print "$file -> $orig\n";}

# __Change versions to current ones if sub-version upgrade
# ..Gnu compiler collection version
    $orig =~ s/${old_sub}/${new_sub}/g;
# ..Apple Darwin version
    $orig =~ s/(darwin)\d{2}\.\d\.\d/$1$new_darwin_version/;

# ..Skip non-existent files
    if (! -e $orig){
        print "\t$orig does not exist. Skip!\n";
        next;
    }
# ..Remove existing files before linking
    if (-e $plain || -l $plain ){
        print "$plain exists\n";
        if ($dryrun) {
            print "\tWould remove $plain\n";
            print "\tunlink $plain\n";
        }
        else {
            unlink $plain or die "Unable to unlink $plain $!\n";
        }
    }
    else {
        print "\t$plain does not exist would create\n";
    }
# ..Finally! link the new version
    if ($dryrun) {
        print "\twould symlink $orig, $plain;\n";
    }
    else {
        symlink $orig, $plain
            or die "Unable to symlink $orig to $plain:$!\n";
    }

}