Split file by vector of line numbers

Question

I have a large file, about 10GB. I have a vector of line numbers which I would like to use to split the file. Ideally I would like to accomplish this using command-line utilitie

Answer 1

Using awk:

$ awk -v v="2 5" '       # space-separated vector if indexes
BEGIN {
    n=split(v,t)         # reshape vector to a hash
    for(i=1;i<=n;i++)
        a[t[i]]
    i=1                  # filename index
}
{
    if(NR in a) {        # file record counter in the vector
        close("file" i)  # close previous file
        i++              # increase filename index
    }
    print > ("file" i)   # output to file
}' file

Sample output:

$ cat file2
4 5 6
7 8 9 
10 11 12