#!/usr/bin/perl

# Keep this sort of configurable for the future.
$GRUBDIR="/boot/grub";

# Parse the menu file, and see if we can get a match for a maybe given arg.
open(MENU, "<$GRUBDIR/menu.lst") || die "no menu.lst in $GRUBDIR";
$gotit = 0;
$titleno = -1;
$global_default = undef;
while(<MENU>) {
  m,^\s*default\s+(.+), && $titleno == -1 && ($global_default = $1);
  next unless m,^\s*title\s+(.*),i;
  $title_name = $1;
  $titleno++;

  if (@ARGV > 0) {
    # Argument may be entirely numerical, in which case it is an index,
    # or a perl RE that leads to the first title matching.
    if (( $ARGV[0] =~ m,^[0-9]+$, && $titleno    eq   $ARGV[0] ) ||
	( $ARGV[0] !~ m,^[0-9]+$, && $title_name =~ m,$ARGV[0],i) ) {
      $gotit = 1;
      last;
    }
  } else {
    print "$titleno: $title_name\n";
  }
}
close(MENU);

print "Warning: you haven't set a global default!\n" if !defined($global_default);

# Without a command line argument, we have now listet the titles and are done.
exit 0 if @ARGV < 1;

# Else the user wants to write the default file. We have better found a match!
if ($gotit > 0) {
  print "Warning: your global default is 'saved'; changing default permanently!"
    if $global_default eq "saved";

  print "Using entry #$titleno: $title_name\n";

  # set the magic one-time flag
  $titleno |= 0x4000;

  open(DEFFILE, ">$GRUBDIR/default") ||
    die "Cannot open default file for writing";
  $buf = $titleno . "\0" .  "\n" x 9;
  syswrite(DEFFILE, $buf, 10);
  close(DEFFILE);

  exit 0;
} else {
  print $ARGV[0] . " not found in $GRUBDIR/menu.lst\n";
  exit 1;
}