Question

There was a similar question here but for excel/vba Excel Macro – Comma Separated Cells to Rows Preserve/Aggregate Column
because i have a big file (>300mb) this is not an option, thus I am struggeling to get it to work in bash.

Based on this data

 1   Cat1                 a,b,c
 2   Cat2                 d
 3   Cat3                 e
 4   Cat4                 f,g

I would like to convert it to:

 1   Cat1                 a
 1   Cat1                 b
 1   Cat1                 c
 2   Cat2                 d
 3   Cat3                 e
 4   Cat4                 f
 4   Cat4                 g

Answer 1

cat > data << EOF
1   Cat1                 a,b,c
2   Cat2                 d
3   Cat3                 e
4   Cat4                 f,g
EOF

set -f                               # turn off globbing
IFS=,                                # prepare for comma-separated data
while IFS=$'\t' read C1 C2 C3; do    # split columns at tabs
    for X in $C3; do                 # split C3 at commas (due to IFS)
        printf '%s\t%s\t%s\n' "$C1" "$C2" "$X"
    done
done < data