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I think this is related to: How can I check if a program exists from a Bash script?

Specifically, I want to run py -m http.server on computers that have py but don't have python3 and I want to run python3 -m http.server on computers that have python3 but not py. I also tried just checking the version number: py -v && py -m http.server; python3 -v && python3 -m http.server but this still seems to have the same problem, and hitting ctrl+C twenty times doesn't kill it.

I tried py && py -m http.server; python3 && python3 -m http.server but I believe it's executing the second command within python. Also, there are other aliases for Python on other computers. I know that I could just set py as an alias for python3, but I'm looking for a universal solution.

(Side note: It really bothers me that this is inconsistent. They should all just work.)

Eventually, I want a script that runs two things in parallel: the first is just npm run dev which has a --watch on it and has to continue to run, and the other is to cd docs/ then use python to host on localhost, then open chrome to localhost:8000, additional help would be much appreciated, still a beginner to Linux.

I also want to make a second command that runs npm run build, changes the second line in docs/sw.js from const dynamicCacheName = 'site-dynamic-vNUMBER'; to replace NUMBER with NUMBER+1.

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  • What scripting language are you targeting? For Bash, add the bash tag. For generic shell, add the shell tag. Commented Feb 6, 2021 at 22:29
  • I'm not sure if it's bash or shell to be honest, I'll have to look into that (sorry I'm not good at this type of stuff). Do shebangs basically set all of them as the same alias so I can just call one? Commented Feb 6, 2021 at 22:51
  • OK, I added the shell tag, since it's generic. Ignore the comment about shebangs; I misunderstood what you're doing. Commented Feb 6, 2021 at 22:55

3 Answers 3

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Does this do what you're after? Assuming bash or similar:

( py -V && py -m http.server ) || ( python3 -V && python3 -m http.server )

On my box this does the following:

$ ( py -V && py -m http.server ) || ( python3 -V && python3 -m http.server )
py: command not found
Python 3.5.2
Serving HTTP on 0.0.0.0 port 8000 ...
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5 Comments

Although if py -m http.server returns false (like if it's killed), then the second part will run anyway.
fair comment ... one could capture return codes for both -V variants and then pick the existing/preferred one ... I was just building on his own approach.
( py -V && py -m http.server ) || ( python3 -V && python3 -m http.server ) seems to be what I was after, thank you! Do you know how to run two processes in parallel by chance? I know && is for if the first succeeds, || is for if the first fails, and ; is run after regardless, but I want them to run in parallel. Anyway, I'll mark this as the answer since it answered my primary question, thank you.
( py -V && py -m http.server& ) ; ( python3 -V && python3 -m http.server& ) ... not sure about "run in parallel", though; as soon as one has grabbed the port the other will fail ...
I mean run in parallel for something else. I now have build and localhost as npm commands, and I'd like to be able to run them at the same time, but currently only one runs: "build": "cross-env NODE_ENV=production postcss src/styles.css -o docs/css/styles.css && cleancss -o docs/css/styles.css docs/css/styles.css", "localhost": "cd docs && ( py -V && py -m http.server ) || ( python3 -V && python3 -m http.server )", "local-dev": "npm run dev && npm run localhost"
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For the second part of your question you could have a small bash script like this (I included the python or py check):

#!/bin/bash

npm run dev --watch &

chromium-browser "http://localhost:8000" 2>/dev/null &

cd docs/ || exit # Exit if the cd command fails
if command -v py -V &> /dev/null; then
    echo "py"
    py -m http.server
elif command -v python3 -V &> /dev/null; then
    echo "python3"
    python3 -m http.server
else
    echo "Neither command found"
fi

& At the end of a command will run it in the background, as written above it will still display the output of the commands.

If you kill the script with CTRL+C it will kill everything, chromium, the python server and the npm run.

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8 Comments

Ooh this looks awesome, thank you, I'll test it right now. So I save it as a .sh file then run sh myfile.sh? I was just trying npm run dev & npm run localhost but after CTRL+C I wasn't able to kill node in the background, even with sudo pkill node and sudo killall node it still shows up in ps
It's in bash (as you can see in the first line), so bash myfile.sh. To kill your node process you need to get its pid using ps -ef and use kill PID
Ah got it. What's the difference between bash and sh? I ran it with bash myfile.sh and it ran, but the npm run dev part isn't going in the background. Both commands need to continue running.
Still cannot kill node: imgur.com/a/1rdpIbC
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I actually wanted to post a full answer since I got what I was after from several answers and comments and chatting with a friend:

I installed the npm package concurrently and then added a local-dev npm script in my package.json:

"scripts": {
    "dev-no-watch": "postcss src/styles.css -o docs/css/styles.css",
    "dev": "postcss src/styles.css -o docs/css/styles.css --watch --verbose",
    "build": "cross-env NODE_ENV=production postcss src/styles.css -o docs/css/styles.css && cleancss -o docs/css/styles.css docs/css/styles.css",
    "localhost": "cd docs && ( py -V && py -m http.server ) || ( python3 -V && python3 -m http.server )",
    "local-dev": "concurrently --kill-others \"npm run dev\" \"npm run localhost\""
},

Which runs both concurrently, and upon hitting ctrl+C, kills both as well.

I of course added localhost from the answer for the original question of detecting python version and running it correctly/failing gracefully, etc, and that works like a charm.

Hope this answer is helpful to someone in the future : )

(Now I just need to find out hos to edit a line of a file from the command line OS independently)

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