awk to compare two files [duplicate] - bash

Question

This question already has answers here:
Fast way of finding lines in one file that are not in another?
(11 answers)
Closed 7 years ago.
I am trying to compare two files and want to print the matching lines... The lines present in the files will be unique
File1.txt
GERMANY
FRANCE
UK
POLLAND
File2.txt
POLLAND
GERMANY
I tried with below command
awk 'BEGIN { FS="\n" } ; NR==FNR{A[$1]++;NEXT}A[$1]' File1.txt File2.txt
but it is printing the matching record twice, I want them to be printed once...
UPDATE
expected output
POLLAND
GERMANY
Current Output
POLLAND
GERMANY
POLLAND
GERMANY

Answer 1

grep together with -f (for file) is best for this:
$ grep -f f1 f2
POLLAND
GERMANY
And in fact, to get exact matches and no regex, use respectively -w and -F:
$ grep -wFf f1 f2
POLLAND
GERMANY
If you really have to do it with awk, then you can use:
$ awk 'FNR==NR {a[$1]; next} $1 in a' f1 f2
POLLAND
GERMANY
FNR==NR is performed when reading the first file.
{a[$1]; next} stores in a[] the lines of the first file and goes to the next line.
$1 in a is evaluated when looping through the second file. It checks if the current line is within the a[] array.
Why wasn't your script working?
Because you used NEXT instead of next. So it was treated as a constant instead of a command.
Also, because the BEGIN { FS="\n" } was wrong, as the default FS is a space and it is ok to be like that. Setting it as a new line was making it misbehave.

Answer 2

Your command should maybe be:
awk 'NR==FNR{A[$1]++;next}A[$1]' file1 file2
You have a stray semi-colon after the closing brace of BEGIN{} and also have "NEXT" in capital letters and have mis-spelled your filename.

Answer 3

Try this one-liner:
awk 'NR==FNR{name[$1]++;next}$1 in name' file1.txt file2.txt
You iterate through first file NR==FNR storing the names in an array called names.
You use next to prevent the second action from happneing until first file is completely stored in array.
Once the first file is complete, you start the next file by checking if it is present in the array. It will print out the name if it exits.
FS is field separator. You don't need to set that to new line. You need RS which is Record Separator to be new line. But we don't do that here because that it the default value.

Answer 4

If you don't have to use awk, a better alternative might be the GNU coreutil, comm. From the man page:
comm -12 file1 file2 Print only lines present in both file1 and file2.