按时间顺序每天使用PHP合并CSV文件的列

Thanks is advance because I am new to PHP. I have a csv file that I need to merge two columns and output to a new csv file once a day automatically.

Source file: ONHAND.csv

Group,Part Number,Free Stk
CAR,12129,1
SUP,1442,10
HUS,53111,203
VIS,4000414,3

Resulting file: ALLIEDSTK.CSV

SKU,QTY
CAR.12129,1
SUP.1442,10
HUS.53111,203
VIS.4000414,3.

Program notes:

1. Notice a period is added between the Group and Part Number values before the output to SKU.
2. I need to be able to set a time for this operation to run once a day.
3. I will need to change a specific Group value before the merge. Example source data: CAR,12129,1 resulting data: MAG.12129,1