Shell Programming and Scripting

awk ' FILENAME=="1.csv"  {arr[$0]++}
      FILENAME=="2.csv"  {arr[$0]++}
      FILENAME=="3.csv"  {arr[$0]++}
      END {for (i in arr) 
      {if(arr[i]==3) {print i, arr[i] } } } ' 1.csv 2.csv 3.csv

nawk ' {
  a[$0]++
}
END{
  for ( i in a )
    if( a[i] >= 3)
      print i
} ' 1.csv 2.csv 3.csv

awk 'END { 
  for (V in v) 
    if (v[V] >= ARGC - 1)
      print V
    }
{ v[$0] += ++f[FILENAME,$0] }
' *csv 

cat <(sort a|uniq) <(sort b | uniq) <(sort c |uniq) | sort | uniq -c |awk '$1==3 {print $2}'

sub fun
{
  open FH,"<$_[0]";
  while(<FH>){
   chomp;
   $hash{$_}->{$_[0]}=1;
  }
  close FH;
}
fun('a.txt');
fun('b.txt');
fun('c.txt');
print join "\n", grep {(keys %{$hash{$_}})==3} keys %hash;

paste -d";" 1.csv 2.csv 3.csv | while IFS=";" read a b c
do 
   if [ "$a" == "$b" -a "$b" == "$c" ];then  
       echo "$a"
   fi
done

exec 4<"1.csv"
exec 5<"2.csv"
exec 6<"3.csv"
while read line1 <&4
do
    read line2 <&5
    read line3 <&6    
    if [ "$line1" == "$line2" -a "$line2" == "$line3" ];then
        echo "$line1 is common"
    fi
done
exec >&4-
exec >&5-
exec >&6-

# This inits the file counter
BEGIN {
        f_num=0
}

# This increments the file counter when we start an input file
(FNR == 1) {
  f_num++
}

# This clause says to add an entry to the table of strings if this is the first file and it is not in the table.
# The value of the entry is the number of the file it was found (always 1 here)
# We also skip the rest of the clauses in the script and go to the next line
(NR == FNR) && !($0 in a) {
        a[$0] = f_num
        next
}

# This clause is executed if the string is in the table and in the last file.  It really means all previous files....
# If it was, we mark as being in this file.  If a string is not in the current file, its value will never be updated again.
($0 in a) && (a[$0] == f_num - 1){
        a[$0] = f_num
}

# Only print the entries that were in all the files (have a value of f_num)
END {
        for (i in a)
                if( a[i] == f_num)
                print i
}