[sed] Insert a line in the middle of an existing configuration file

Playing with Testing a new piece of software using a Vagrant box, I created a in which I had to insert the line sql-mode=NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION inside an existing MySQL config file. I had to put it inside a specific section, so I targeted a line starting with datadir.

The following sed command will add the new line above it. It will update the config file by using a temporary intermediate file.

sed -n 'H;${x;s/^\n//;s/datadir.*$/sql-mode=NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION\n&/;p;}' /your/file.cnf > tmp && mv tmp /your/file.cnf

How do I add a line of text to the middle of a file using bash?

Redirect output from sed 's/c/d/' myFile to myFile

[Android] Accessing your application files from Android Studio

While learning to play with SQLite databases in Android, I wanted to check the .db file generated by my code in the emulator. I was unable to find it directly with the built-in Files application because it doesn't let us see system folders.

The built-in Files app

Fortunately, Android Studio 3+ comes with the Device File Explorer, which allows us to browse system files and access the root data folder. To open it, go to View > Tool Windows > Device File Explorer. My application data was stored in /data/data/.

How to display the Device File Explorer

How to see the data stored in sqlite in android studio using genymotion as emulator

[Git] List the files which have been modified between two commits/tags

I needed to know the exact list of files that had been modified between my last two tags:

git diff --name-only v2.0.0 v2.0.1

You can replace the tags by commits:

git diff --name-only SHA1 SHA2
git diff --name-only HEAD~10 HEAD~5


Merge two versions of a file with git-checkout

I have slightly different i3 configuration files between my desktop and laptop computers. In this case, the laptop keyboard is missing a Play/Pause multimedia key. This is where the two files differ: the laptop has a different key binding for running the music player.

Having recently added new key bindings to the desktop configuration, I wanted to merge those new lines into the laptop configuration file, without overwriting its specific lines. After trials and errors and thanks to precious clues found on the Internet, I found the patch flag of git-checkout. From the branch specific to my laptop configuration, I ran:

$ git checkout -p master .config/i3/config

This displays an output similar to git-diff, based on the local file .config/i3/config and the one in the branch 'master'. For each conflicts, Git asks:

Apply this hunk to index and worktree [y,n,q,a,d,/,j,J,g,e,?]?

I answered 'n'o to preserve the part specific to the laptop, and 'y'es for the new key bindings I wanted to copy.

Output of $ git checkout -p

Nuke (remove all traces) of a file in Git history

First note: if you are not alone on the project, consult with your colleagues before doing this. Because we are about to rewrite history and other contributors will be forced to manually rewrite their history too.

Second note: if what you want to remove is sensitive material (e.g. passwords), consider everything compromised. Unless you are 100% sure that absolutely no one has had any access to your repository. And you are not, are you? Even with your super-secure unbreakable security measures... No, you are not.

Okay, you have been warned.

Let's say we want to remove all traces of a file named "hardcoded_passphrase.txt". We need the sha1 of the commit where this file first appeared. If you don't know, just use the first commit. In this example, the sha1 is bb9c2d4:

$ git filter-branch --index-filter 'git update-index --remove path/to/hardcoded_passphrase.txt' bb9c2d4..HEAD
$ git push --force --verbose --dry-run
$ git push --force