Question

I am currently attempting to merge two different text files in a perl script – However its a bit more complicated than that.

The problem (slightly altered for the sake of easy explanation):

I have two different text files, one named dog1.txt and one named dog2.txt (as shown below).

dog1.txt
    poodle     8888
    jackrussel    5743
    beagle     6784

dog2.txt 
    spaniel    9843
    poodle    3756
    germanshepard    3267
    beagle    3478  

As you can see poodle and beagle are contained in both text files, but with different four digit codes associated with them.

What I want is a new file created that merges these two files together AND if there are any duplicates, such as poodle and beagle, I want the new file to contain the four digit associated with poodle and beagle to come from the dog1.txt file instead of dog2.txt.

The new file would need to look like this (it does not matter about the order of the dog names, its the numbers associated with them that need to be correct):

final_dog.txt
    poodle    8888
    germanshepard    3267
    jackrussel    5743
    beagle    6784
    spaniel    9843

I have tried many varying solutions, but none reliably work the way I need it to.

Any help is greatly appreciated, thanks

Answer 1

You basically want to print the first instance you encounter. As such, you can use the standard idiom for removing duplicates.

perl -lane'print if !$seen{$F[0]}++' dog1.txt dog2.txt >final_dog.txt

This approach uses the least amount of memory. It also starts producing output the earliest possible (useful if you’re piping the output).

---

To meet the new requirement, use

perl -lane'print if @F==2 && $F[1]=~/^\d+\z/ && !$seen{$F[0]}++' \
   dog1.txt dog2.txt >final_dog.txt