Files with AWK

Diff.awk

#! /bin/awk
# Here's an awk scrip that atttemps to set difference of two files based on their first column
# gawk -f Diff.awk file1.txt file2.txt
BEGIN{

 OFS=FS="\t"
    file = ARGV[1]
    while (getline < file)
        Contained[$1] = $1
    delete ARGV[1]
    }
!($1 in Contained){
    print $0
}

part_file.awk

awk -v filename="archivo_grande.txt" -v partsize="1000000" '
    BEGIN {part = 1; file = filename "_" part ".txt"; size = 0}
    {
      size += length + 1; 
      if (size > partsize) {
        close(file); 
        part++;
        file = filename "_" part ".txt";
        size = 0
      } 
      print > file
    }
    END {close(file)}
' archivo_grande.txt