Shell Programming and Scripting

need to be able to capture a file with the following conditions:
The filenames are, for example, 3526_332840.dat, where 3526 is constant, and 332840 is a sequential number which is always a couple hundred greater than the previous day's file.
I want to be able to change this script to acoomplish what I want

Can somebody explain what this does. (how I can change this to accomplish what I want?)

#Determine if there is a file to process
ls 3987*.dat > /dev/null 2>&1

if [ $? != 0 ]
then
exit
fi

for i in 3987*.dat
do


# Capture just the file sequence number
fseqno=`print $i | sed 's/.*_//' | sed 's/.dat//' `

cd $SOFTPATH/data/finaid/idoc
echo $i `date` > idochd1.lst

cp $i idoc.dat

cd $SOFTPATH/bin

cp $i idoc.dat

cd $SOFTPATH/bin

# Load file into tables
cd $SOFTPATH/script
sqlplus / @$SOFTPATH/script/rypidoc_loadcss_run.sql $fseqno
==============

It is not clear what you want - give us example expected output. Also there seem to be logic errors and other issues in the script you presented.