Join two files on Linux

Question

I have two files; I want to join them.

$cat t1
 1 1.2
 2 2.2
$cat t2
 1
 2
 1

I want to have the output below

$cat joind.tx         


        

Answer 1

A simple awk is suffice for this:

awk 'FNR==NR{a[$1]=$2;next} {print $1, a[$1]}' t1 t2
1 1.2
2 2.2
1 1.2

Breakup:

NR == FNR {                  # While processing the first file
  a[$1] = $2                 # store the second field by the first
  next                       # move to next record in 1st file
}
{                            # while processing the second file
  print $1, a[$1]            # print $1 and the remembered
                             # value from the first file.
}