UNIX for Dummies Questions & Answers

$ cat Test1.txt
Amar,Movies,12
Sanjay,Cricket,18
Rakesh,Football,35
Samit,Cricket,56
Sam,Songs,20
Ram,Books,40
$

$ cat Test2.txt
1,Samit,Service
2,Sam,DJ
3,Rakesh,Police
$

Amar,Movies,,
Sanjay,Cricket,,
Rakesh,Football,3,Police
Samit,Cricket,1,Service
Sam,Songs,2,DJ
Ram,Books,,

awk 'NR==FNR{A[$2]=$1; B[$2]=$3; next} {$3=A[$1]; $4=B[$1]}1' FS=, OFS=, file2 file1

awk 'NR==FNR{A[$2]=$1 FS $3; next} {$3=$1 in A?A[$1]:FS}1' FS=, OFS=, file file1

awk '				# Invoke awk with this script...
NR == FNR {			# If the number of lines read from all files
				# (NR) is equal to the number of lines read
				# from the current input file (FNR) (which in
				# this case means if we are looking at a line
				# from file2)...
	A[$2] = $1		# Create an array (A[]) indexed by field 2 ($2)
				# on the current line whose value is set to
				# field 1 ($1) on the current line.
	B[$2] = $3		# Create an array (B[]) indexed by field 2 ($2)
				# on the current line whose value is set to
				# field 3 ($3) on the current line.
	next			# Skip to next input line and restart
				# processing at the top of htis script.
}
{				# If we got to here, we are looking at a line
				# from file1...
	$3 = A[$1]		# Set field 3 on this line to what was saved in
				# array A[] indexed by the contents of field 1
				# on this line (A[$1]).
	$4 = B[$1]		# Set field 4 on this line to what was saved in
				# array B[] indexed by the contents of field 1
				# on this line (B[$1]).
}
1				# Perform the default action (print the current
				# contents of the current line).
' FS=, OFS=, file2 file1	# End the script ('), set the input field
				# separator to a comma (FS=,), set the output
				# field separator to a comma (OFS=,) and name
				# the two files to be processed by this awk
				# script (file2 file1).

$ awk 'NR==FNR{A[$2]=$1; B[$2]=$3; next} {$3=A[$1]; $4=B[$1]}1' FS=, OFS=, Test2.txt Test1.txt
Amar,Movies,,
Sanjay,Cricket,,
Rakesh,Football,3,Police
Samit,Cricket,1,Service
Sam,Songs,2,DJ
Ram,Books,,

$ awk 'NR==FNR{A[$2]=$1; B[$2]=$3; print FILENAME,$1,$2,$3,A[$2],B[$2]; next} {$3=A[$1];$4=B[$1];print FILENAME,$1,A[$1],B[$1]}' FS=, OFS=, Test2.txt Test1.txt
Test2.txt,1,Samit,Service,1,Service
Test2.txt,2,Sam,DJ,2,DJ
Test2.txt,3,Rakesh,Police,3,Police
Test1.txt,Amar,,
Test1.txt,Sanjay,,
Test1.txt,Rakesh,3,Police
Test1.txt,Samit,1,Service
Test1.txt,Sam,2,DJ
Test1.txt,Ram,,