CODEWITHSUNDEEP
awk
Ibrahim Quraish
Ibrahim Quraish

Reputation: 4099

awk compare two files gives unexpected output when swapping the position of argument files

Below are my two files' content:

cat f1 

9  
5  
3

cat f2 

1  
2  
3

This is my code, which works perfectly and gives output as per my understanding: 

awk 'NR==FNR {a[$0]; next} FNR in a' f1 f2
3

But, when I swap the position of these 2 argument files, the output is different than what I expected.

awk 'NR==FNR {a[$0]; next} FNR in a' f2 f1  
9  
5  
3

I expected the output as 3 again as like previous, because f2 and f1 both has exactly 3 lines and the key 3 is however stored in the hash map. Please explain how the 2nd code works.

Upvotes: 0

Views: 29

Answers (1)

Jonathan Leffler
Jonathan Leffler

Reputation: 754410

The output from the second example is, of course, correct.

Since f2 contains the values 1, 2, 3, the array a ends up with elements a[1], a[2], and a[3]. When it is processing f1, line 1 has FNR == 1, and 1 is an index in a, so line 1 (containing 9) is printed; similarly for lines 2 and 3, hence the output you see.

Upvotes: 1

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