regex question matching dates



given then ARGV[0] is 2008052803, why woulnd't below regex match them??

} elsif ( $ARGV[0] =~ m/\b2008[01][1-31]([01][0-9]|2[0-3])\b/ ) {
@array = qx#ls -tr $directory/$ARGV[0]*#;
#2008052803
.