Here is the file content :
$head abc.txt
20070301130052,xxz
20070307132111,cvasjchgjhcg
gacg
chjbgasjkchjk
20070307133029,gcvashcvgjchklk
20070308070017,hbcjkbgcjkhk
20070308084700,hjcgjhcg
20070308114137,kjcghjk

$tail abc.txt
20080304113050,cgsjkchskjchskch
20080304113053,cvbnsckhhkhcjs
cjksdhcklsjcl
20080304120046,cvbsdcbksdhj
cvhbskcvnhsdkl
svjscvkmj
20080304120048,vgsdjkv
vbsdkvhj
vnsdvlmj
vnm