Evgeni Golov: I just want to run this one Python script
So I couldn't sleep the other night, and my brain wanted to think about odd problems
Ever had a script that's compatible with both, Python 2 and 3, but you didn't want to bother the user to know which interpreter to call? Maybe because the script is often used in environments where only one Python is available (as either
/usr/bin/python OR /usr/bin/python3) and users just expect things to work? And it's only that one script file, no package, no additional wrapper script, nothing.
Yes, this is a rather odd scenario. And yes, using Python doesn't make it easier, but trust me, you wouldn't want to implement the same in bash.
Nothing that you will read from here on should ever be actually implemented, it will summon dragons and kill kittens. But it was a fun midnight thought, and I like to share nightmares!
The nice thing about Python is it supports docstrings, essentially strings you can put inside your code which are kind of comments, but without being hidden inside commnent blocks. These are often used for documentation that you can reach using Python's help() function. (Did I mention I love help()?)
Bash on the other hand, does not support docstrings. Even better, it doesn't give a damn whether you quote commands or not. You can call "ls" and you'll get your directory listing the same way as with ls.
Now, nobody would under normal circumstances quote ls. Parameters to it, sure, those can contain special characters, but ls?!
Another nice thing about Python: it doesn't do any weird string interpolation by default (ssssh, f-strings are cool, but not default). So "$(ls)" is exactly that, a string containing a Dollar sign, an open parenthesis, the characters "l" and "s" and a closing parenthesis.
Bash, well, Bash will run ls, right?
If you don't yet know where this is going, you have a clean mind, enjoy it while it lasts!
So another thing that Bash has is exec: "replace[s] the shell without creating a new process". That means that if you write exec python in your script, the process will be replaced with Python, and when the Python process ends, your script ends, as Bash isn't running anymore. Well, technically, your script ended the moment exec was called, as at that point there was no more Bash process to execute the script further.
Using exec is a pretty common technique if you want to setup the environment for a program and then call it, without Bash hanging around any longer as it's not needed.
So we could have a script like this:
#!/bin/bash exec python myscript.py "$@"Here
"$@" essentially means "pass all parameters that were passed to this Bash script to the Python call" (see parameter expansion).
We could also write it like this:
#!/bin/bash "exec" "python" "myscript.py" "$@"As far as Bash is concerned, this is the same script. But it just became valid Python, as for Python those are just docstrings. So, given this is a valid Bash script and a valid Python script now, can we make it do something useful in the Python part? Sure!
#!/bin/bash "exec" "python" "myscript.py" "$@" print("lol")If we call this using Bash, it never gets further than the
exec line, and when called using Python it will print lol as that's the only effective Python statement in that file.
Okay, but what if this script would be called myscript.py? Exactly, calling it with Python would print lol and calling it with Bash would end up printing lol too (because it gets re-executed with Python).
We can even make it name-agnostic, as Bash knows the name of the script we called:
#!/bin/bash "exec" "python" "$0" "$@" print("lol")But this is still calling
python, and it could be python3 on the target (or even something worse, but we're not writing a Halloween story here!).
Enter another Bash command: command (SCNR!), especially "The -v option causes a single word indicating the command or file name used to invoke command to be displayed". It will also exit non-zero if the command is not found, so we can do things like $(command -v python3 command -v python) to find a Python on the system.
#!/bin/bash "exec" "$(command -v python3 command -v python)" "$0" "$@" print("lol")Not well readable, huh? Variables help!
#!/bin/bash __PYTHON="$(command -v python3 command -v python)" "exec" "$ __PYTHON " "$0" "$@" print("lol")For Python the variable assignment is just a var with a weird string, for Bash it gets executed and we store the result. Nice! Now we have a Bash header that will find a working Python and then re-execute itself using said Python, allowing us to use some proper scripting language. If you're worried that
$0 won't point at the right file, just wrap it with some readlink -f .
Wishing everyone in Debian good health and prosperity in the Gujarati New Year Vikram Samvat 2078 called Pramadi.
Last year I started collecting ideas of things I would like to 3D print
one day, on Twitter. Twitter is fundamentally ephemeral, so I'll collect
it here instead. I got up to 14 items on Twitter, and now I'm up to 25.
I don't own a 3D printer, but I have access to one at the work office.
Perhaps this list is my subconcious trying to convince me to buy one.
What am I missing? What else should I be thinking of printing? Let me
know!
We (Robert Tari, the UBports developers team, myself) are very close to releasing Ayatana Indicators 0.9.x. The work on Ayatana Indicators is currently nearly completed funded by the UBports Foundation and over the past half year, many many changes, improvements and clean-ups have been added to the code.
Ayatana Indicators 0.9.x will be the first release series to be in the development tree of Ubuntu Touch 20.04 (which is currently under very heavy development).
Ayatana Indicators 0.9.x will also be used in various other desktop environments available in upcoming Ubuntu 22.04 LTS, such as Ubuntu MATE, Xubuntu, (optionally in) Ubuntu Budgie (please correct my wording, if you know better), (send me a note, if I forgot your desktop env), etc.
So, to all Ubuntu Touch, Ubuntu MATE, Xubuntu, etc. users. If you not already are a translator of Ayatana Indicators and you are good in English and fluent in at least one other language, please consider helping out with translating or improving translations of Ayatana Indicators.
The translation work needs to be done on Hosted Weblate [1], please sign up for an account (if you haven't done so, yet) and chime in.
Thanks so much for your contributions!
light+love
Ever considered doing research about online communities, free culture/software, and peer production full time? It s PhD admission season and my research group 
An updated version 0.2.2 of the random-number generator tester 
In October I was assigned 1.25 hours of work by Freexian's Debian LTS
initiative and carried over 28.75 hours from earlier months. I worked
14.75 hours and will carry over the remainder.
I updated the linux-4.19 package to merge in the changes in buster
release 10.11, uploaded that and issued