file name1:seq.txt
-------------------
>ID_101
AGCTGAGTAGACTGA
>ID_102
CGATGCTAGCTAGCTACAT
>ID_103
ATCTTATCTTTTTATACC

file name2:seq_updated.txt
--------------------------
>ID_104
AATAGCTAGAAGGA
>ID_105
AGATCGACTGAA
>ID_106
ACTAGCTACGATATATTATATATAT

my php page:
-----------
$foo="ID_106" //ID to be searched.
$cmd="perl split.pl $foo";
echo exec($cmd);

my perl program:
---------------
$bar=$ARGV[0];
print exec("grep -h -A 1 $bar *.txt");