How can I merge WiFi passwords from a backup and from the current configuration? I have an old backup of the WiFi passwords on my Nexus 7. I also have a new configuration which has some passwords that are newer and some that are older.

How can I merge the configuration in a controlled manner without having to entrust my WiFi passwords to some third-party app?
If you have root access on your device:


Grab a copy of /data/misc/wifi/wpa_supplicant.conf, e.g. using adb pull, and save it to your computer
Restore the data from your backup, and grab a copy of that in the same manner
Use a text editor, and merge the entries to a new file
Put that file back into place, e.g. using adb push
Make sure the file is owned by system:wifi and has permissions 664.


Without root access, it might be possible as well, but would be much more tricky (plus the overhead would probably not be worth it). The following is untested, and requires at least Android 4.0:


Create an adb backup
Restore the "old data" to your device
Create another adb backup
Extract both backups to different locations on your device (see: [How do you extract an App's data from a full backup made through “adb backup”?])(How do you extract an App&#39;s data from a full backup made through &quot;adb backup&quot;?)
Merge the data from both wpa_supplicant.conf files
Re-assemble the backup file
Restore the re-assembled backup




A third way lies in between, but does not require to re-assemble and restore the backup file, nor to replace the wpa_supplicant.conf directly. But you will need a copy of that file, which you either can obtain via adb pull or by extracting the backup files.

Once you've got a copy of both files, you can simply read your connection data, and enter those you wish manually: everything is stored as plain-text here, completely unencrypted (including the passwords!). An example entry (slightly modified to hide the real data):

network={
    ssid="smartcafe"
    psk="cafesmart"
    key_mgmt=WPA-PSK
    priority=46
}


As you see: if you would like to use that data for the APN "smartcafe", simply edit your config and put the corresponding password (psk):


Go to Settings → WiFi
Scroll to the APN
Long-press its entry, select "Change"
Enter the new password


If it should be a new entry: At the same place, at the bottom of the screen, tap the "add network" button, and enter the data you've read from the file.