ln

ln (English: /lɑːn/) is a natural way to consume the git log. This is an entirely opinionated wrapper for git log, and to some extent it's really just a really convoluted shell alias for git log.

If you want something pretty darn close, feel free to simply

$ LN_FMT='%C(yellow)%h%C(auto)%d %Creset%s %C(241)(%C(246)%ar%C(241))%Creset'
$ git config set pretty.ln $LN_FMT
$ git log --graph --oneline --format=ln

Architecture

ln spawns a total of 3 child processes.

1. An exec() call to git log.
2. A parser that reads the output of git log and does simple string parsing to make the output pretty.
3. An exec() call to less with STDIN piped so it appears as though we did something like git log | less in a shell.

And for that we need two pipes.

╭─────────╮   pipe #1   ╭─────────╮   pipe #2   ╭─────────╮
│ git log ├─────────────┤ printer ├─────────────┤  less   │
│   (A)   ├[1]───────[0]┤   (B)   ├[1]───────[0]┤   (C)   │
╰─────────╯             ╰─────────╯             ╰─────────╯

It is possible that the git log output is bigger than the (fixed) capacity of the pipe #1. This is important because while debugging if you don't let (B) read continuously from pipe #1, then there is a chance that (A) would block on writing to that pipe. Likewise for pipe #2.

You might be wondering why must we fork one last time to run less. Why not just call exec() on the parent process and hand control to less? That's pretty much what it would look like with the shell command git log | less right? Well, we fork a child process for less because it consumes STDIN lazily (it doesn't flush/clear STDIN upon exit). So if we call exec("less", ...) on the parent process and less exits early, then we might be back in the situation in the previous paragraph where the (B) blocks on writing to pipe #2, causing ln to survive as a zombie process.

CLI argument handling

ln does basically no CLI argument parsing. It looks out for one and only one flag, --bound. This will tell ln to truncate the git log output to the height of the terminal window, if such a terminal window exists. All other CLI arguments are passed straight on to the exec() call to git log.

Installing

To install ln, simply run

$ make configure
$ make install

In particular, a binary called git-ln will be installed (to whichever prefix you set in CMakeLists.txt). This allows you to run git ln (without the hyphen), enabling commands like git -C <repo> ln --all.

On memory safety

There is a quick and simple valgrind command in the Makefile to evaluate ln's memory profile. It does find one leak when ln is compiled with glibc, but that's due to fdopen's leak ( (cf) here and here).