Compare two files and list common lines

You can use the awk command to compare two files and show the common ones. Compared to the Linux command “comm”, advantages of using “awk” is it will give output though the files are not sorted.
Syntax :

awk 'NR==FNR{a[$1]++;next} a[$1] ' file1 file2

Eg :

[root@test]# cat A
apple
orange
mango
grape

[root@test]# cat B
mango
banana
grape

[root@test]# awk 'NR==FNR{a[$1]++;next} a[$1] ' A B
mango
grape