Shell Programming and Scripting

host1,neighbor1
host3,neighbor4
host2,neighbor1
host2,neighbor3
host1,neighbor3
host3,neighbor1
host1,neighbor2
host3,neighbor2

host1,neighbor1,neighbor3,neighbor2
host2,neighbor1,neighbor3
host3,neighbor4,neighbor1,neighbor2

bash-2.05a$ cat inputfile 
host1,neighbor1
host3,neighbor4
host2,neighbor1
host2,neighbor3
host1,neighbor3
host3,neighbor1
host1,neighbor2
host3,neighbor2
bash-2.05a$ cat itinshell.sh 
#!/bin/sh
for k in `cat inputfile | awk -F, '{print $1}' | sort -u`
do
  /usr/ucb/echo -n $k
  for i in `grep $k inputfile | awk -F, '{print $2}'`
  do
    /usr/ucb/echo -n ",$i"
  done
  echo
done
bash-2.05a$ ./itinshell.sh 
host1,neighbor1,neighbor3,neighbor2
host2,neighbor1,neighbor3
host3,neighbor4,neighbor1,neighbor2

$ cat file
host1,neighbor1
host3,neighbor4
host2,neighbor1
host2,neighbor3
host1,neighbor3
host3,neighbor1
host1,neighbor2
host3,neighbor2
$ perl -F, -ane'
  chomp $F[1];$_{$F[0]}.=",".$F[1];
  print map "$_$_{$_}\n", sort keys %_ if eof
  ' file
host1,neighbor1,neighbor3,neighbor2
host2,neighbor1,neighbor3
host3,neighbor4,neighbor1,neighbor2

#! usr/bin/perl
open FH,"<a.txt";
while(<FH>){
	my @arr=split(",",$_);
	map {tr/\n//d} @arr;
	$hash{$arr[0]}=$hash{$arr[0]}.",".$arr[1];
}
for $key (keys %hash){
	print $key,$hash{$key},"\n";
}