Shell Programming and Scripting

group1	user1
	user2
	user3
group2	user4
	user5
	user1
group3	user6
	user7
	user8

group1
group2

BEGIN
{
  i=0;                                  # declaring variable
}

{
  if (NF==2){currgrp=$1;}               # check whether awk actually processing 2 column record, if yes save the group name
  else
     {
      if ($1~/uname/)                   # else if awk is processing 1 column record and is found user name, save the group name to array and increment i
       {
         netgroups[i]=currgrp;
         i++;
       }
     }
}

END                                     # at the end of processing whole file print the array (all saved groups)
{
  for(j=0;j<i;j++)
  {
    print netgroups[i];
  }
}

awk -v uname="user1" -f awkscript.awk group_file