Introduction to Bash Scripting

https://github.com/bobbyiliev/introduction-to-bash-scripting

by RafelMri • 2 years ago

151 118 2 years ago

jofer4• 2 years ago

For anyone wondering whether or not you really need to know bash: Yes. Yes, you do.

Somewhere in the middle of every stack is a bunch of bash and makefiles. Don't replace that or avoid it. Embrace it. It's not perfect, but it's important to know.

almostgotcaught6• 2 years ago

I love when people proclaim this as if it's some kind of sage wisdom when it's actually just hypermyopia. For anyone wondering whether this is true: of course it's not since there are plenty of stacks that don't run in environments that are anywhere near a shell.

jofer4• 2 years ago

Can you seriously name something other than very low level embedded software that doesn't involve shell at some level? I certainly can't...

wpm3• 2 years ago

Whether they run in environments where a shell is nearby has no bearing on whether they are built or tested in environments where a shell is near and sufficient for the task.

benreesman• 2 years ago

Some things change: you once needed Perl where you now need Python.

Other things don’t: you need non-trivial bash.

I don’t mind if people do their heavy lifting in VSCode, I like the tool myself.

But if you can’t unfuck the little daemon that VSCode talks to?

You’re out of commission. You’re at the mercy of people who can.

udev40963• 2 years ago

This looks extremely basic. I would instead recommend reading https://bash.academy or TLDP Advance Bash Scripting Guide

imp0cat• 2 years ago

That's a good thing, isn't it? It's not too scary for someone who's not well versed in shell scripting. And you can later move on to other resources (TLDP is great!).

wyclif• 2 years ago

I looked at it this morning and I think it's helpful for those brand new to the shell. My only criticism of it is that it needs a once-over edit by a native English speaker. The exercises seem fine to me.

callalex• 2 years ago

Can someone name me examples of where a bash script is actually the _correct_ tool for the job in modern times? Or is it still used only because it’s the easily available tool?

jofer4• 2 years ago

Any time you're running lots of CLI utilities directly is a good start. Bash is very very good for that, and other than perl, most other things aren't particularly good at it.

lambdaba• 2 years ago

Ruby is the greatest at it and inline deps make it perfect for scripting.

jcranmer2• 2 years ago

Unless you need to run programs with arguments with spaces in their name.

Not that long ago, I needed to write a script that would grab the last command in a shell file that had a list of commands, add an argument or two to it, and run it. Which proceeded to barf because the command had quotes, for some of the arguments had necessary spaces in them, and I couldn't figure out the way to get the necessary string in a way that bash could properly execute the command. My eventual solution was to just use python's shlex module to parse the line and output an executable command (and remark that I should have just started the script in Python in the first place)...

yjftsjthsd-h4• 2 years ago

Shell is good for running a bunch of other programs and doing file operations. In that niche it seems unbeatable, and outside that niche it's generally a terrible choice.

citizen_friend• 2 years ago

Its always a great tool if you need to automate a computer task.

voidfunc• 2 years ago

Almost never but there's a lot of folks that have gaslit themselves into believing "its the right tool for the job".

There's no requirement that a shell language suck as much as bash.

patmcc• 2 years ago

There's a server. You can ssh into it, but you don't have root. You don't know if it'll have python (2 or 3), perl, ruby, node, whatever. You need to write a cronjob that'll run every 5 minutes, or a script that'll do something on-demand, or just a one-off to clean some stuff up or grab particular log files or something. Performance isn't going to be a problem. User input isn't going to be a problem.

If you never run into this problem, fair enough, maybe you don't need bash.

A lot of us do.

NegativeLatency2• 2 years ago

I've used linux brew a couple of times to escape this problem, able to get a newer version of python or ruby instead of bash: https://docs.brew.sh/Homebrew-on-Linux

pxc3• 2 years ago

Nix is great for this, if you have the disk space. It's nicest if Nix is already installed on the box by a sysadmin, but you can use it in a pivot_root environment if you don't have a cooperative sysadmin.

mediumsmart• 2 years ago

I don’t know if it’s the correct tool but my llm used it to replace a weather widget iFrame hazard on a static site. It’s a cronjob that lynxdumps the weather forecast, writes the values into an html block and then sshs into the clients server that has the site (but no lynx) and replaces the html block in all html files. Runs every hour and might work for years, we shall see.

rty322• 2 years ago

I know basic bash and can read most bash scripts, but never spent much time on it to become an expert. However I found ChatGPT to be extremely valuable -- given the description of a task, it can create very high quality scripts with best practice and comments, often correctly using third party tools. That's probably what I'll do going forward -- my time is better spent creating a good prompt and reviewing output.

dools• 2 years ago

Same, and another great thing I have been using since ChatGPT made it trivial to do so is systemd. I was using pm2 quite a bit for running scripts but high quality bash (or python or php or whatever really) plus systemd is really killer.

I’ve also been doing way more with google cloud shell. I was always such a point and click guy when it came to setting stuff up in GCP but automating and scripting with bash in cloud shell using ChatGPT is so much faster and repeatable.

wpm3• 2 years ago

Depends on the platform. macOS has a terminal and ChatGPT is highly Linux biased, and it's quite happy to spew trash when you point out "hey bozo I said macOS useradd isn't a real command on macOS".

TechDebtDevin• 2 years ago

I'm pretty sure most llms have very low eval scores on bash compared to other common languages.

DonHopkins• 2 years ago

And most humans have MUCH MUCH lower eval scores on bash, yet they write it anyway, and the rest of us get stuck with trying to use and understand and debug and maintain that crap, that bursts into fire and explosive diarrhea whenever it hits and edge condition or file name with a space in it.

rty322• 2 years ago

Well, from what I can see ChatGPT can already write much better bash scripts than I do, so...

asicsp• 2 years ago

https://www.shellcheck.net/ is amazing to spot pitfalls.

See my list https://learnbyexample.github.io/curated_resources/linux_cli... for learning resources for CLI tools, scripting, etc.

jimmar• 2 years ago

I've coded in a bunch of languages over my career, but somehow managed not to use bash. But a few weeks ago I found myself needing to create a somewhat involved script using Bash. Using GitHub Copilot, I was able to generate a script that worked great and it included comments, arrays, arguments, case statements, loops, conditionals, menus, etc--basically covering the first dozen chapters of this book. I guess my point is that we need to teach people what's possible and to help them explain what they want clearly. Memorizing syntax will be a less relevant skill at some point.

guappa5• 2 years ago

I haven't seen your script but I bet it will break in a hundreds corner cases.

qz_kb4• 2 years ago

Using python and constraining yourself to only use a basic subset of the standard library modules so you can run the script in pretty much any environment is almost always a better choice than trying to write even one loop, if statement, or argument parser in a bash script.

bash script is "okay" I guess if your "script" is just a series of commands with no control flow.

NegativeLatency2• 2 years ago

Had decent luck using chatgpt to translate some crufty old bash deploy scripts to python

isbvhodnvemrwvn• 2 years ago

I would agree if python dependency management wasn't a dumpster fire.

rendaw2• 2 years ago

I think the point GP was making was that you restrict yourself to only the bundled standard library, which covers most of the basics needed for scripting.

qz_kb4• 2 years ago

This is why you force yourself to use nearly zero dependencies. The standard library sys, os, subprocess, and argparse modules should be all you need to do all the fancy stuff you might try with bash, and have extremely high compatibility with any python3.x install.

guappa5• 2 years ago

And it's a dumpster fire because they refuse to make any decision and decide which is the supported way.

Instead they removed distutils, so now there is no way to install any module without using a 3rd party installer.

rendaw2• 2 years ago

I agree, but I've been having a hard time even with python recently. I had a small script (50-100 lines) to format a data drive on boot I refactored, 3 or 4 obvious undeclared variables and who knows how many more I didn't notice - mypy found 0 issues.

I was looking up statically typed alternatives and stumbled upon Ammonite and Scala-CLI for scala. I haven't used them much, but Ammonite bundles some basic libraries including command line parsing, http, and json, which are probably 99% of what I used in Python too? And Scala seems like an interesting language too with decent editor integration.

macrael2• 2 years ago

use mypy!

wiseowise6• 2 years ago

I had a small script (50-100 lines) to format a data drive on boot I refactored, 3 or 4 obvious undeclared variables and who knows how many more I didn't notice - mypy found 0 issues.

What does pyright/pylance say?

aulin• 2 years ago

Choice is a privilege you rarely have in a day to day job. Bash most of the time is already there and you have to live with it.

Also, I've been forced to work on a huge SCons based project and I guarantee python can make your life quite miserable when used for something it's not supposed to.

qz_kb4• 2 years ago

I'm not suggesting you build a a whole build system with python (which is basically bazel and it seems to be good enough for google.)

A lot of originally little automation/dev scripts bloat into more complicated things as edge cases are bolted on and bash scripts become abominations in these cases almost immediately.

guappa5• 2 years ago

Using python and constraining yourself to only use a basic subset of the standard library modules

Used to be a viable strategy until they started to drop modules from the standard library at every single release.

yawpitch3• 2 years ago

Used to be a viable strategy until they started to drop modules from the standard library at every single release.

That’s a bit of a ridiculous statement, there’s a small number of very-long deprecated modules removed in 3.12, and some more recently deprecated modules in 3.13. And these things are old, largely or completely unmaintained, and usually complete obsolete.

I’d be surprised if anyone has a script that’s been adversely effected by this, and if they did it’s because they stopped maintaining it years ago (and also chose to both silence warnings and upgrade interpreter versions without reading the release notes).

udev40963• 2 years ago

Bash is native. You won't find python pre-installed on all distros, like alpine

yawpitch3• 2 years ago

True, though there’s a whole world of people who will yell at you for using Bash-isms rather than pure posix precisely because Bash (at least up to date versions) isn’t everywhere either.

hi_hi• 2 years ago

Bash may be native, but alot of the programs you'll want to call may not be, or will differ between platforms in subtle ways. Although this won't be a concern for small/trivial scripts, but if we're talking about python as an alternative, my point probably still applies.

lloeki3• 2 years ago

You won't find python pre-installed on all distros, like alpine

The same can be said of bash, especially since you mention Alpine (also FreeBSD)

Perl, though... ;)

(if Perl is not there it gets pulled in very quickly as a dependency of something, e.g typically you pull git, you get perl)

runjake• 2 years ago

As a person who’s been doing shell programming for 35 years and Python for 15 years, I completely disagree.

Bash scripts and Bash control flow has been and is used in highly critical scripts all over the place, including other planets.

We’ve been writing reliable, well-designed scripts for many decades. Some of my scripts are several hundred lines long and older than the system engineers currently occupying their positions.

Python is fine too. Use the right tool for the right job.

mazambazz• 2 years ago

Hard disagree. I've written plenty in both. They both have their strengths, but bash is just more efficient if you're working with the filesystem. The UNIX philosophy of "do one thing and do it well" shines here. Python is more powerful but it's a double-edged sword. If I want to read a file containing API endpoints, send a request to them for some JSON, and do some parsing, I don't want to need or want to deal with importing modules, opening file objects, using dictionaries, methods, functions, etc.

Why do that when I can literally just ``` N=0 while read -r URL; do curl "$URL" | jq '.data[].someProp' | grep -v "filter" > "$N.data" N="$((N+1))" done < ./links.txt ```

The other thing is bash makes it exceptionally easier to integrate across different system tools. Need to grab something from a remote with `rsync`, edit some exif, upload it to a CDN? That's 3 commands in a row, versus god knows what libraries, objects, and methods you need to deal with in Python.

qz_kb4• 2 years ago

now add error handling.

skydhash2• 2 years ago

Libraries are nice, until you have to write the glue code between the modules and functions. But sometimes you already have the features you want as programs and you just need to do some basic manipulation with their arguments and outputs. And the string model can work well in that case.

wiseowise6• 2 years ago

Why do that when I can literally just ``` N=0 while read -r URL; do curl "$URL" | jq '.data[].someProp' | grep -v "filter" > "$N.data" N="$((N+1))" done < ./links.txt ```

So that other people can read and modify this.

baxuz2• 2 years ago

Tried https://github.com/google/zx and never looked back.

pindab0ter• 2 years ago

That's not available on basically every system.

What advantages does zx have over Python, Ruby or even Fish for example, if we're installing extra programming languages?

baxuz2• 2 years ago

It's what fits my use case quite well.

vwkd• 2 years ago

How about dax[^1] which is cross-platform and also works with Deno?

[^1]: https://github.com/dsherret/dax

ayakang314153• 2 years ago

Is there anything Bash does that Python can't do? I feel like using Python is just way better than using Bash.

wpm3• 2 years ago

Work out of the box on any macOS/Linux computer.

ayakang314153• 2 years ago

You use Bash for that not because it is better, but because UNIX related binaries are configured in Bash.

cassianoleal3• 2 years ago

Is there anything Python does that Bash can't do?

There are many reasons to use either. Probably about as many as there are to use the other. Choose wisely.

ayakang314153• 2 years ago

Yeah, lots of things Python can do but Bash cannot simply because of vast selection of third party modules available in Python.

macrael2• 2 years ago

Write scripts in whatever tooling you have setup for your app. In a typescript codebase, I write typescript scripts. In a go codebase I write go scripts. It's so easy to write a couple wrappers to make execing something a one liner and then the advantages of bash have disappeared. You already have a toolchain for running a program in your language, just use that to build your scripts.

xlii• 2 years ago

Recently I’ve been exploring back Perl. I loved it many years ago and today I just need “glue”.

It seems to be quite fast, can escape UNIX-Linux idiosyncrasies and I still can see all the magic variables in the code after those years.

Maybe it’s better to just get back into Perl instead of figuring out how to pipe back to back to few applications and jq on top?

kamaal• 2 years ago

If you are using Bash, you probably need to use Perl.

Python unfortunately doesn't shine where Perl is good at. Mostly of the command line work involves passing around adhoc text, parsing and using it.

You are better off using a language designed to do that very task than use something else.

udev40963• 2 years ago

If anyone's looking to write tests for bash scripts, I wrote a small blog post few weeks ago: https://hcrypt.net/test.html

tjoff• 2 years ago

A lot of people suggests python, I'd argue that python is a bad fit for what many bash scripts does.

A bash script is basically scripting what you do on your terminal. I feel like scripting in the same language that is your terminal interface is underrated.

You can basically take a look at your command history and wrap it up as a script.

Yes, bash is clunky as hell. It has some really ugly warts. But learning the basics will make you more proficient in the terminal. The synergies are really nice.

_xiaz• 2 years ago

As a linux admin, bash and python are my bread and butter. I have two heuristics for choosing between them: - If it needs more math than counting, choose Python - If it's >200 lines (500 if I'm brave), choose Python

Otherwise, shell scripting is nice

rcxdude• 2 years ago

my heuristic is "if there's an if statement, loop, or variable substitution with uncontrolled input, use python".

lloeki3• 2 years ago

Interesting that a lot of the (general, not specifically here) commentary is "don't use bash, use python" which I find quite clunky, noisy, and boilerplatey to do the same thing as a shell script. Kinda Master Foo and the Ten Thousand Lines†.

Ruby's https://github.com/ruby/shell (which used to be bundled in Ruby itself) doesn't get much mention but is much more clear and useful to me.

    # system commands are not defined by default, only builtins, for safety
    Shell.def_system_command 'ls'
    Shell.def_system_command 'grep'
    Shell.def_system_command 'jq'

    Shell.new.transact do
      # simple redirs just work
      ls | grep('test') > 'some/file'
      ls | grep('other') | tee('foo') >> 'some/file'
      
      # pops at the end of the block
      cd 'some/dir' do
        # nested redir for demo
        (cat < 'foo.json') | jq '.[] | { bar: .bar }'
      end
    end

† http://www.catb.org/esr/writings/unix-koans/ten-thousand.htm...

kmarc• 2 years ago

Similar as plumbum for python

https://pypi.org/project/plumbum/

(also supports dispatching commands to SSH sessions)

csomar• 2 years ago

It’s also something that LLMs generate really well. So you can build reasonably complex scripts with little knowledge of bash.

j0hnyl• 2 years ago

This holds for most scripting options.

d0mine• 2 years ago

You could use both Bash and Python for tasks they are good at: concisely creating one-line shell pipelines in Bash and implementing complex logic that glues together these pipelines in Python.

Example: pyinvoke/fabric https://www.fabfile.org

TheLoafOfBread• 2 years ago

Or you can use PowerShell - Available on MacOS, Windows, Linux instead of suffering through incoherent syntax of Bash.

alwinaugustin• 2 years ago

I am new to bash and always struck at using the tools like `awk` and `sed.` You need to be good at regular expressions to write a good script using these tools.

pronoiac• 2 years ago

I recently was running a variety of compressors over the course of days, and using Bash was great because, it doesn't parse the whole file before it starts running - I could edit and reprioritize next steps while the script was running. "Oh, that one's not working, skip the slower version" or "oh, space is an issue, work on freeing that up." It's a weird hack I wouldn't suggest in production, but it worked well for me.

foreigner• 2 years ago

Debating the pros and cons of different languages misses the point IMO. Shell scripts are useful not because of the language but because the interpreter is already available absolutely everywhere.

1vuio0pswjnm7• 2 years ago

Bash is not a good shell for scripting. Too big and slow.

bobbyiliev• 2 years ago

Many people are saying that ChatGPT or Copilot could write great scripts which is indeed true, but the eBook was written way before those LLMs were a thing. It is still good to learn the basics though.

ngcc_hk• 2 years ago

Bash scripting is hard ... missing a space or add a space ...

How do you debug it and trace it ...

I do use it as said this is the terminal command line and both Mac/Linux supported it. And if it works, it work even nohup.

Just hard.

kchr• 2 years ago

You debug it with shellcheck[0] and `set -ex` (which will trace each statement on STDOUT).

[0] https://www.shellcheck.net/

Too2• 2 years ago

Just skimmed through the book and noticed several examples where it doesn't use argument quoting. For example the first chapter about variables doing echo $name. In fact, there is no mention of argument quoting at all. This should be the number one lesson before touching any bash script. Otherwise your scripts will be vulnerable to command injection. I recommend running the whole book through shellcheck.

It also recommends wrapping variables with curly braces like ${name}, without explaining why, later on never does so itself throughout the rest of the book. There are a lot of such missing explanations in the whole book. It does make it short and fun to jump straight into the examples but i think it could benefit from some facts and reference material, at least to link to.

Anyway, seems like most people here are more interested in arguing over bash vs python than discussing the actual content. A little surprising to see this get so many points.

Introduction to Bash Scripting

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