What is FNR in AWK

What are NR and FNR and what does "NR == FNR" mean?


I am learning file comparison with.

I found syntax like below,

I couldn't understand the meaning of this. Then if I try, do I get the same output?

What exactly is it doing?



Reply:


In awk refers to the record number (usually the line number) in the current file and the entire record number. The operator is a comparison operator that returns true if the two surrounding operands are equal.

This means that the condition only applies to the first file, but since it is reset to 1 for the first line of each file, it continues to increase.

This pattern is typically used to take action on the first file only. The inside of the block means that all further commands will be skipped, so they will only be executed on files other than the first.

The condition compares the same two operands as, so it behaves the same way.






Look in file2 for keys (first word of the line) that are also in file1.
Step 1: Fill in array a with the first few words from file 1:

Step 2: fill in array a and ignore file 2 in the same command. To do this, check the total number of previous data records with the number of the current input file.

Step 3: ignore actions that may occur while parsing File 1

Step 4: Print the key from file2 if it is found in the array. A.




Look it up in the awk manual and then ask yourself what the condition is in the following example:






There are built-in variables.

- It indicates the total number of data records processed.

- It gives the total number of records for each input file.


Suppose you have files a.txt and b.txt with

Remember that NR and FNR awk are built-in variables. NR - Indicates the total number of records processed. (in this case both in a.txt and in b.txt) FNR - Indicates the total number of records for each input file (records in a.txt or b.txt).

Let add "Next" to skip the first NR == FNR match

in b.txt and in a.txt

in b.txt but not in a.txt

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