Shell Programming and Scripting

awk -v left="tab1.txt" -v right="tab2.txt" '
    BEGIN {
        # Read right-side into cache now
        while (getline < right)
        {
            if (!ridx) { rhead=$0; ridx=1 }
            else
            {
                rquery[ridx]=$1; rtype[ridx]=$2
                rstart[ridx]=$3; rstop[ridx]=$4
                ridx++
            }
        }

        # Process left-side one line at a time
        while (getline < left)
        {
            if (!lidx)
            {
                print $0 "\t" rhead "\tDifference"
                lidx=1
            }
            else
            {
                lquery=$1; lstop=$4

                # Find corresponding right-side
                for (i=1; i<ridx; i++)
                {
                    diff=rstop[i]-lstop
                    if (rquery[i]==lquery && diff < 3000)
                    {
                        print $0 "\t" rquery[i] "\t" rtype[i] "\t" \
                                rstart[i] "\t" rstop[i] "\t" diff
                    }
                }
            }
        }
    }'