Shell script for merging dotenv files with duplicate keys

Question

Given two dotenv files,

# file1
FOO="X"
BAR="B"

and

# file2
FOO="A"
BAZ="C"

I want to run

$ ./merge.sh file1.env file2.env > file3.env

to get the following output:

# file3
FOO="A"
BAR="B"
BAZ="C"

So far, I used the python-dotenv module to parse the files into dictionaries, merge them and write them back. However, I feel like there should be a simple solution in shell that rids myself of a third-party module for such a basic task.

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Answer

Alright, so I ended up using

$ sort -u -t '=' -k 1,1 file1 file2 | grep -v '^$\|^\s*\#' > file3

which omits blank lines and comments. Nevertheless, the proposed awk solution works just as fine.

Answer 1

Another quite simple approach is to use sort:

sort -u -t '=' -k 1,1 file1 file2 > file3

results in a file where the keys from file1 take precedence over the keys from file2.

Answer 2

Using a simple awk script:

awk -F= '{a[$1]=$2}END{for(i in a) print i "=" a[i]}' file1 file2

This stores all key values in the array a and prints the array content when both files are parsed.

The keys that are in file2 override the ones in file1.