Today I Learned
The F# language has built in support for annotating numeric values with units, and for such values it appears will do some dimensional analysis and statically complain if units are incorrect.
It’s unclear if there’s a large benefit in having this functionality in the core language rather than …
mpv and youtube-dl can talk directly to each other.
Specificaly:
$ mpv --ytdl-format=bestaudio ytdl://ytsearch:'think about things'
will immediately start mpv off playing the audio results of the youtube-dl search.
Returning a non-object as a JSON response (in particular returning an array) used to be a security vulnerability.
Prefixing (custom) HTTP Headers with X- is actually deprecated / no longer recommended by the IETF.
As of OpenSSH 8.2, OpenSSH now supports U2F for authentication.
This is a totally separate authentication mechanism entirely from say, ED25519 host keys with a second factor; here, the U2F (e.g. Yubikey) is / has the key on it.
To use it though, both sides (server and client) have …
PEP 405 introduced a pyvenv.cfg file, useful for creating lightweight virtual environments without the hacks done by virtualenv historically. Doing so is much, much faster as well, since now creation of a virtual environment is essentially just creating 2 files (one file and a symlink).
It also though changed …
namei(1) (provided by util-linux on macOS) is a nifty utility for fully resolving symbolic links.
Given a chain of links, it will show e.g.:
⊙ namei =python julian@Air ●
f: /Users/julian/.local/bin/python
d /
d Users
d julian
l .local -> /Users/julian/.dotfiles/.local
d /
d Users …
The Firefox Dev Tools console defines a copy() function which will copy text to the clipboard.
For some reason, using navigator.clipboard.writeText("asdf"), which seems to be the normal way to do this fires a rejected promise. Probably something to do with …
A restricted subset of C is compiled via clang to eBPF bytecode, and the Linux kernel contains a JIT (and of course a VM) to execute it.
bcc is a higher level toolkit for interacting with eBPF (including via Python). For example:
from bcc import BPF
BPF(
text …
-S will disable soft line breaks within less, allowing horizontal scrolling.
Use less +F instead of tail -f. It works the same, but supports interrupting the stream with SIGINT to e.g. search around, and then can resume tailing by hitting F again.
Doing so will …
Piping using foo &| bar will pipe both stdout and stderr to bar.
With MULTIOS enabled, multiple outputs to the same file descriptor can be provided, similar to using tee.
In other words:
$ date >foo >bar
will output date to both foo and bar. (Piping it will also work since …
mkdir -p will create a directory with its parents. But cp takes a parents option as well.
cp --parents foo/bar/baz/quux.txt some/directory will create some/directory/foo/bar/baz/quux.txt without any of the other directory structure from the original location.
dstat can replace a bunch of other statistical performance counting things (I/O, CPU, Disk, Network, Syscalls, etc.).
Use socat instead of netcat. It takes something more like endpoint syntax (and does many more kinds of ports and configurable connectivity that come with them).
Tons of examples here.
git you magnificent beast…
log -L :foo will show you the history of the function/object called foo. This is a smarter version of normal log -L which just knows about lines.
But because I’m lazy to even type this out …
pv is a useful utility to insert in shell pipelines for watching how much data passes through the pipe.
This page has a few simple examples, and there are more I’m sure with some googling around.