将一个大文件分割成N个小文件

#!/bin/sh

do_help()
{
    echo "syntax:"
    echo "split "
}

orig_file=$1
split_num=${2:-2}
dest_path=${3:-.}

if ! ( [ -f "$orig_file" ] &&
[ -r "$orig_file" ] && [ -s "$orig_file" ] ); then
    echo "file $orig_file is invalid."
    do_help
    exit 1
fi

if ! [ $split_num -gt 1 ]; then
    echo "split_num is invalid."
    do_help
    exit 1
fi

if ! ( [ -d $dest_path ] && [ -x $dest_path ] );then
    echo "dest_path is invalid."
    do_help
    exit 1
fi

size=$(ls -l $orig_file | awk '{print $5}')
split_size_avr=$(($size/$split_num))
bs=1

if [ $size -gt $((1024*1024)) ]; then
    bs=1024
    split_size_avr=$(($split_size_avr/1024))
fi

for i in $(seq $split_num);do
    if [ $i -eq 1 ]; then
        dd if=$orig_file \
of=$dest_path/${orig_file}.$i bs=$bs count=$split_size_avr
    elif [ $i -eq  $split_num ];then
        dd if=$orig_file \
of=$dest_path/${orig_file}.$i bs=$bs \
skip=$(($split_size_avr*$(($i-1)))) \
count=$(( $size - $(($split_size_avr*$(($i-1)))) ))
    else
        dd if=$orig_file \
of=$dest_path/${orig_file}.$i bs=$bs \
skip=$(($split_size_avr*$(($i-1)))) \
count=$split_size_avr

    fi
done

命令格式：
./split filename N dest_path

合并N个小文件为一个大文件：

代码:
cat $(ls |grep -E 'filename\.') > filename