Shell Programming and Scripting

i/P file
12  NIL ABD LON
11  NIL ABC SIG    <= First duplicate for 3rd column need to be removed
12  NIL ABC AMR
13  NIL ABC AMR
11  NIL ABK AMR

O/P desired based on 3rd column
12  NIL ABD LON
12  NIL ABC AMR
13  NIL ABC AMR
11  NIL ABK AMR

awk 'NR==FNR{A[$3]++;next}{if(A[$3] > 1 && !B[$3]){B[$3]++;next} }1' file file

12  NIL ABD LON
12  NIL ABC AMR
13  NIL ABC AMR
11  NIL ABK AMR

awk 'NR==FNR{a[$3]++;next}a[$3]>1{a[$3]=0; next}1' file file

awk 'NR==1 {print} f ~ $3 && i == 0 {i++;} f ~ $3 && i > 0 {print $0;i=0;j=1} f !~ $3 && j==1  {print $0} {f=$3;}'  file_name

12  NIL ABD LON
12  NIL ABC AMR
13  NIL ABC AMR
11  NIL ABK AMR

awk '{first=($3!=p3)} (first==0 || pfirst==0); {p3=$3; pfirst=first}' file

awk '{first=($3!=p3)} {print pfirst,first,":",$0} {p3=$3; pfirst=first}' file