Shell Programming and Scripting

$ cat file
x a 10
y a 10
z a 11
x b 10
y b 12
z b 10
x c 0
y c 0
x d 1
y d 1
z d 1
w d 2
x e 1
y e 1
z e 1

$ sort -u -k 2,3 file | nawk 'BEGIN {a=$2} {if($2==a && NF > 0){print $2}}{a=$2}'
a
b
d

$ for i in `sort -u -k 2,3 file | nawk 'BEGIN {a=$2} {if($2==a && NF > 0){print $2}}{a=$2}'`; do nawk -v var=$i '$2 == var {print $0}' file; done
x a 10
y a 10
z a 11
x b 10
y b 12
z b 10
x d 1
y d 1
z d 1
w d 2

#!/usr/bin/perl
use strict;
my (%hash,%h);
open FH,"<a";
while(<FH>){
  my @tmp=split(" ",$_);
  $hash{$tmp[1]}.=$_;
  $h{$tmp[1]}->{$tmp[2]}=1;
}
close FH;
for my $key (sort keys %hash){
  my @tmp=keys %{$h{$key}};
  print $hash{$key} if $#tmp>=1;
}

#! /bin/bash
gawk 'BEGIN{
while (getline < "file") {
  twothree[$2$3]=$2;
}
for (i in twothree) {
  if (twothree[i] in two) {
    filtered[twothree[i]];}
  else {
    two[twothree[i]];}
}}
{if ($2 in filtered) {print $0;}
}' file