Shell Programming and Scripting

NAME, FAV_FOOD, FAV_DRINK, ID, GENDER
Bob, Fish, Coke, 1, M
Lisa, Rice, Water, 2, F
Jenny, Noodle, Tea, 3, F
Ken, Pizza, Coffee, 4, M
Lisa, Cake, Milk, 2, F
Ken, Sandwich, Juice, 4, M

NAME, ID, AGE, COUNTRY
Lisa, 2, F, 22, UK 
Ken, 4, M, 12, Iceland
Jenny, 3, F, 18, France
Bob, 1, M, 31, Ireland

NAME, FAV_FOOD, FAV_DRINK, ID, GENDER, AGE, COUNTRY
Bob, Fish, Coke, 1, M, 31, Ireland
Lisa, Rice, Water, 2, F, 22, UK 
Jenny, Noodle, Tea, 3, F, 18, France
Ken, Pizza, Coffee, 4, M, 12, Iceland
Lisa, Cake, Milk, 2, F, 22, UK 
Ken, Sandwich, Juice, 4, M, 12, Iceland

awk 'FNR==NR{A[$1]=$1;next} ($1 in A){print $0 FS A[$1]} !($1 in A){print $0}' file1 FS=, file2

awk 'FNR==NR{T[$1]=$3 FS $4; next} {print $0, T[$1]}' file2 file1

cat Input_file2
NAME, ID, GENDER, AGE, COUNTRY
Lisa, 2, F, 22, UK
Ken, 4, M, 12, Iceland
Jenny, 3, F, 18, France
Bob, 1, M, 31, Ireland

awk -F"," 'FNR==NR{A[$1 FS $2]=$4 FS $5;next} ($1 FS $(NF-1) in A){print $0 FS A[$1 FS $(NF-1)]}' Input_file2 Input_file1

NAME, FAV_FOOD, FAV_DRINK, ID, GENDER, AGE, COUNTRY
Bob, Fish, Coke, 1, M, 31, Ireland
Lisa, Rice, Water, 2, F, 22, UK
Jenny, Noodle, Tea, 3, F, 18, France
Ken, Pizza, Coffee, 4, M, 12, Iceland
Lisa, Cake, Milk, 2, F, 22, UK
Ken, Sandwich, Juice, 4, M , 12, Iceland

awk -F","                       ######## Making field separator as comma(,) here.
'FNR==NR{                       ######## Putting condition FNR==NR which will only be TRUE when first file(Input_file2) in this example will be TRUE, where FNR is a awk's variable which will be REST each time a new file is being read and NR will be keep on increasing till the all files being read completely. NR(Number of records)
A[$1 FS $2]=$4 FS $5;           ######## Making an array named A whose index is $1 and field separator and value of $2, then assigning A's value to $4 and $5's value, where $1 is first field of line, $2 is 2nd field, $3 is 3rd field and $4 is fourth field etc.
next}                           ######## here I am using next statement which tells awk NOT to process further statements.
($1 FS $(NF-1) in A){           ######## Now while second file(Input_file1) in this example is being read if $1 field separator and 2nd last column($(NF-1)) if these values are present as an index into array A. then perform the following statements.
print $0 FS A[$1 FS $(NF-1)]    ######## Now print the value of complete line with value of array A whose index is $1 field seprator $(NF-1).
}' Input_file2 Input_file1      ######## mentioning here both of the input files.

awk '   
FNR == NR       {T[$1,$2] = $0
                 sub ("^" $1 FS $2 FS $3, "", T[$1,$2])
                 next
                }
$1,$4 in T      {print $0  T[$1,$4]
                }
' FS=, file2 file1
NAME, FAV_FOOD, FAV_DRINK, ID, GENDER, COUNTRY
Bob, Fish, Coke, 1, M , 31, Ireland
Lisa, Rice, Water, 2, F , 22, UK
Jenny, Noodle, Tea, 3, F , 18, France
Ken, Pizza, Coffee, 4, M , 12, Iceland
Lisa, Cake, Milk, 2, F , 22, UK
Ken, Sandwich, Juice, 4, M , 12, Iceland