Shell Programming and Scripting

John  254
Chris 254
Matt  123
Abe   123
Raj    487
Moh   487

254 John,Chris
123 Matt,Abe
487 Raj,Moh

awk '!a[$2]{b[++i]=$2} {a[$2]=a[$2]?a[$2] "," $1:$1} END{for(j=1;j<=i;j++){print b[j],a[b[j]]}}'  Input_file

awk '
function prt() { if (NR>1) print p1, p2 }
{ if ($2!=p2) { prt(); p1=$1; p2=$2 } else { p1=(p1 "," $1) } }
END { prt() }
' inputfile

 awk '
!a[$2]{                      ## checking if an array named a whose index is $2 is having NULL value for current second field, if yes then do following.
  b[++i]=$2                  ## create array b element whose index is incrementing by 1 value of variable i and value is current $2.
}
{
  a[$2]=a[$2]?a[$2] "," $1:$1## creating array a with index $2 and concatenating in its own value.
}
END{                         ## END block for awk code now.
  for(j=1;j<=i;j++){         ## starting a for loop from variable j value 1 to till i value.
    print b[j],a[b[j]]       ## printing value of array b whose index is variable j then printing array a value whose index is value of array b whose index is j.
}
}
' Input_file                 ## Mentioning the Input_file here.