Comparing two environment properties files and have only the added properties in the new file migrated to the old file - linux

Question

Hello here is a setup of what im trying to accomplish
The user has one environment properties file on their machine, it has a list of say 300 properties.
We then deploy a new build to that same system with an updated version of that file with a few more properties added. I do not want to get rid of the old env prop file i just want to add those new properties without the user having to do it. example
File A (New Environment Properties file)
DB_CONNECTION=
DB_REPO=
DB_TEST=
DB_USER=
File B (Old environment properties)
DB_REPO=
DB_USER=
I just need the DB_CONNECTION and DB_TEST added to that file, there may be more to add this is just an example.
I have tried multiple grep and diff commands but they just output the screen or replace the whole file. I don't want to do this since the user has saved values so i just need the new properties added.
Thanks in advance

Answer 1

I propose to source each file in its own subshell, execute set to show the complete set of environment variables, and compare both outputs. Sounds complex but is typed rather easily:
diff <(source a.sh; set) <(source b.sh; set)
The output is a typical diff output, in my case:
19d18
< DB_CONNECTION=
21d19
< DB_TEST=
87c85
< _=a.sh
---
> _=b.sh
The last two lines (_=a.sh and _=b.sh) are not interesting; they just show the last used argument (which differs of course).
Now, to add the found stuff to the file you want to patch, you can use this:
diff <(source a.sh; set) <(source b.sh; set) | grep '^<' | cut -c3- | grep -v '^_=' >> b.sh
This solution does not consider changed values, though. If the user changed a value in his old config file, the new config file will have the standard value again, this will be a difference, so it will be added to the old config file.
You might not want this, so you might want to specify further requirements on how to handle changed values.

Answer 2

I went with the following this will basically merge the old properties along with the values for each and add all the new properties. At the end of the script I just have the following command
sed -i 'property/d' environment.properties
Here is the merge script a co-worker helped me with
#!/bin/bash
old_file=
new_file=
while read new_line; do
# Check to see if the current line is a comment.
comment=$(echo "${new_line}" | grep '^[ \t]*[#!]')
# Print comments as-is.
if [ -n "${comment}" ]; then
echo "${new_line}"
continue
fi
# Get the property key.
key=$(echo "${new_line}" | sed -e 's/^[ \t]*\([^=:]\+\).*/\1/')
# If the line isn't a comment or a property, skip it.
if [ -z "${key}" ]; then
echo "ERROR: invalid property: ${new_line}" 1>&2
continue
fi
# Get the old value for the key.
old_line=$(grep "^[ \t]*${key}[ \t]*[=:]" ${old_file})
if [ -n "${old_line}" ]; then
# If there is an old value, used it.
echo "${old_line}" | sed -e 's/^[ \t]*//'
else
# Otherwise, use the new value.
echo "${new_line}"
echo "WARN: new property: ${key}" 1>&2
fi
done < ${new_file}
Thank you for the help