$ cat formula.csv
a,b,c
1,=2+3,4
6,,7,=8+9,

$ perl -MCSV -e'$_ = dcsv (in => "formula.csv", bom => 1, formula => "diag")'
Field 2 (column: 'b') in record 1 contains formula '=2+3'
Field 4 in record 2 contains formula '=8+9'