DB<200> $str=join "","δφόΔΦάί"

  DB<201> printf '\\x%X,',$_ for unpack 'C*',$str
 => ""
\xC3,\xA4,\xC3,\xB6,\xC3,\xBC,\xC3,\x84,\xC3,\x96,\xC3,\x9C,\xC3,\x9F,