mktorrent wrapper

#!/bin/bash

# first save off the positional parameters
OPTIONS=("$@")

# then find the last one, presumably the file or dir being dot torrented
while [[ $# -gt 1 ]]; do
    shift
done
target="$1"

# the max size for a given piece length in KB, or KiB if you prefer
#
PLMAXES=([15]=51200 [16]=102400 [17]=204800 [18]=409600 \
        [19]=819200 [20]=1638400 [21]=3276800 [22]=6553600)
pl="0"

# if the target exists, get the size of it and use that size to find the right
# piece length by comparing to the max size for a given piece length. if it is
# not smaller than any max size, use the piece length one larger than the
# highest one with a max size.
#
# if the target doesn't seem to exist, call mktorrent with the original options
# and let mktorrent give the error message as if the wrapper wasn't even here.
#
if [ -e "$target" ]; then
    tsize=`du -sk "$target" | cut -f1`
    for ((i = 15; i < 23 && pl == 0; i++)); do
        if [[ $tsize -le ${PLMAXES[$i]} ]]; then
            pl=$i
        fi
    done
    if [[ $pl -eq 0 ]]; then
        pl=$i
    fi
    mktorrent --piece-length=${pl} "${OPTIONS[@]}"
else
    mktorrent "${OPTIONS[@]}"
fi