Shell Programming and Scripting

awk '{a[$1]++;b[$1]=$0}END{for (i in a) if (a[i]==1) print b[i]}' file

$ awk '{ U[$1]++; L[NR]=$0 }
END {
        for(N=1; N<=NR; N++)
        {
                $0=L[N];
                if(U[$1] > 1) continue; # Skip non-unique column 1
                print;
        }
}' data

3 5
2 5

$

awk '{print $1}' input | sort | uniq -u | while read key
do
        grep \^"${key} " input
done

./scriptname
2 5
3 5