Explanation for newbies:
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Shell is the programming language that you use when you open a terminal on linux or mac os. Well, actually “shell” is a family of languages with many different implementations (bash, dash, ash, zsh, ksh, fish, …)
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Writing programs in shell (called “shell scripts”) is a harrowing experience because the language is optimized for interactive use at a terminal, not writing extensive applications
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The two lines in the meme change the shell’s behavior to be slightly less headache-inducing for the programmer:
set -euo pipefail
is the short form of the following three commands:set -e
: exit on the first command that fails, rather than plowing through ignoring all errorsset -u
: treat references to undefined variables as errorsset -o pipefail
: If a command piped into another command fails, treat that as an error
export LC_ALL=C
tells other programs to not do weird things depending on locale. For example, it forcesseq
to output numbers with a period as the decimal separator, even on systems where coma is the default decimal separator (russian, dutch, etc.).
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The title text references “posix”, which is a document that standardizes, among other things, what features a shell must have. Posix does not require a shell to implement
pipefail
, so if you want your script to run on as many different platforms as possible, then you cannot use that feature.
Nushell has pipefail by default (plus an actual error system that integrates with status codes) and has actual number values, don’t have these problems
Powershell is the future
- Windows and office365 admins
I even use powershell as my main scripting language on my Mac now. I’ve come around.
That’s sounds terrible honestly
~$ man !!
Lol, I love that someone made this. What if your input has newlines tho, gotta use that NUL terminator!
God, I wish more tools had nice NUL-separated output. Looking at you,
jq
. I dunno why this issue has been open for so long, but it hurts me. Like, they’ve gone back and forth on this so many times…
Gotta love a meme that comes with a
man
page!People say that if you have to explain the joke then it’s not funny. Not here, here the explanation is part of the joke.
It is different in spoken form, written form (chat) and written as a post (like here).
In person, you get a reaction almost immediately. Written as a short chat, you also get a reaction. But like this is more of an accessibility thing rather than the joke not being funny. You know, like those text descriptions of an image (usually for memes).
This is much better than a man page. Like, have you seen those things?
I really recommend that if you haven’t, that you look at the Bash’s man page.
It’s just amazing.
Come to think of it, I probably have never done so. Now I’m scared.
I’m divided between saying it’s really great or that it should be a book and the man page should be something else.
Good thing man has search, bad thing a lot of people don’t know about that.
I think you mean a
man
zing.I’ll see myself out.
set -euo pipefail
is, in my opinion, an antipattern. This page does a really good job of explaining why. pipefail is occasionally useful, but should be toggled on and off as needed, not left on. IMO, people should just write shell the way they write go, handling every command that could fail individually. it’s easy if you write adie
function like this:die () { message="$1"; shift return_code="${1:-1}" printf '%s\n' "$message" 1>&2 exit "$return_code" } # we should exit if, say, cd fails cd /tmp || die "Failed to cd /tmp while attempting to scrozzle foo $foo" # downloading something? handle the error. Don't like ternary syntax? use if if ! wget https://someheinousbullshit.com/"$foo"; then die "failed to get unscrozzled foo $foo" fi
It only takes a little bit of extra effort to handle the errors individually, and you get much more reliable shell scripts. To replace -u, just use shellcheck with your editor when writing scripts. I’d also highly recommend https://mywiki.wooledge.org/ as a resource for all things POSIX shell or Bash.
Putting
or die “blah blah”
after every line in your script seems much less elegant than op’s solutionThe issue with
set -e
is that it’s hideously broken and inconsistent. Let me copy the examples from the wiki I linked.
Or, “so you think set -e is OK, huh?”
Exercise 1: why doesn’t this example print anything?
#!/usr/bin/env bash set -e i=0 let i++ echo "i is $i"
Exercise 2: why does this one sometimes appear to work? In which versions of bash does it work, and in which versions does it fail?
#!/usr/bin/env bash set -e i=0 ((i++)) echo "i is $i"
Exercise 3: why aren’t these two scripts identical?
#!/usr/bin/env bash set -e test -d nosuchdir && echo no dir echo survived
#!/usr/bin/env bash set -e f() { test -d nosuchdir && echo no dir; } f echo survived
Exercise 4: why aren’t these two scripts identical?
set -e f() { test -d nosuchdir && echo no dir; } f echo survived
set -e f() { if test -d nosuchdir; then echo no dir; fi; } f echo survived
Exercise 5: under what conditions will this fail?
set -e read -r foo < configfile
And now, back to your regularly scheduled comment reply.
set -e
would absolutely be more elegant if it worked in a way that was easy to understand. I would be shouting its praises from my rooftop if it could make Bash into less of a pile of flaming plop. Unfortunately ,set -e
is, by necessity, a labyrinthian mess of fucked up hacks.Let me leave you with a allegory about
set -e
copied directly from that same wiki page. It’s too long for me to post it in this comment, so I’ll respond to myself.From https://mywiki.wooledge.org/BashFAQ/105
Once upon a time, a man with a dirty lab coat and long, uncombed hair showed up at the town police station, demanding to see the chief of police. “I’ve done it!” he exclaimed. “I’ve built the perfect criminal-catching robot!”
The police chief was skeptical, but decided that it might be worth the time to see what the man had invented. Also, he secretly thought, it might be a somewhat unwise move to completely alienate the mad scientist and his army of hunter robots.
So, the man explained to the police chief how his invention could tell the difference between a criminal and law-abiding citizen using a series of heuristics. “It’s especially good at spotting recently escaped prisoners!” he said. “Guaranteed non-lethal restraints!”
Frowning and increasingly skeptical, the police chief nevertheless allowed the man to demonstrate one robot for a week. They decided that the robot should patrol around the jail. Sure enough, there was a jailbreak a few days later, and an inmate digging up through the ground outside of the prison facility was grabbed by the robot and carried back inside the prison.
The surprised police chief allowed the robot to patrol a wider area. The next day, the chief received an angry call from the zookeeper. It seems the robot had cut through the bars of one of the animal cages, grabbed the animal, and delivered it to the prison.
The chief confronted the robot’s inventor, who asked what animal it was. “A zebra,” replied the police chief. The man slapped his head and exclaimed, “Curses! It was fooled by the black and white stripes! I shall have to recalibrate!” And so the man set about rewriting the robot’s code. Black and white stripes would indicate an escaped inmate UNLESS the inmate had more than two legs. Then it should be left alone.
The robot was redeployed with the updated code, and seemed to be operating well enough for a few days. Then on Saturday, a mob of children in soccer clothing, followed by their parents, descended on the police station. After the chaos subsided, the chief was told that the robot had absconded with the referee right in the middle of a soccer game.
Scowling, the chief reported this to the scientist, who performed a second calibration. Black and white stripes would indicate an escaped inmate UNLESS the inmate had more than two legs OR had a whistle on a necklace.
Despite the second calibration, the police chief declared that the robot would no longer be allowed to operate in his town. However, the news of the robot had spread, and requests from many larger cities were pouring in. The inventor made dozens more robots, and shipped them off to eager police stations around the nation. Every time a robot grabbed something that wasn’t an escaped inmate, the scientist was consulted, and the robot was recalibrated.
Unfortunately, the inventor was just one man, and he didn’t have the time or the resources to recalibrate EVERY robot whenever one of them went awry. The robot in Shangri-La was recalibrated not to grab a grave-digger working on a cold winter night while wearing a ski mask, and the robot in Xanadu was recalibrated not to capture a black and white television set that showed a movie about a prison break, and so on. But the robot in Xanadu would still grab grave-diggers with ski masks (which it turns out was not common due to Xanadu’s warmer climate), and the robot in Shangri-La was still a menace to old televisions (of which there were very few, the people of Shangri-La being on the average more wealthy than those of Xanadu).
So, after a few years, there were different revisions of the criminal-catching robot in most of the major cities. In some places, a clever criminal could avoid capture by wearing a whistle on a string around the neck. In others, one would be well-advised not to wear orange clothing in certain rural areas, no matter how close to the Harvest Festival it was, unless one also wore the traditional black triangular eye-paint of the Pumpkin King.
Many people thought, “This is lunacy!” But others thought the robots did more good than harm, all things considered, and so in some places the robots are used, while in other places they are shunned.
The end.
This is great and thanks for taking the time to enlighten us 😄
No worries! Bash was my first language, and I still unaccountably love it after 15 years. I hate it and say mean things about it, but I’m usually pleased when I get to write some serious Bash.
Exercise 6:
set -e f() { false; echo survived; } if ! f; then :; fi
That one was fun to learn.
Even with all the jank and unreliability, I think
set -e
does still have some value as a last resort for preventing unfortunate accidents. As long as you don’t use it for implicit control flow, it usually (exercise 6 notwithstanding) does what it needs to do and fails early when some command unexpectedly returns an error.I personally don’t believe there’s a case for it in the scripts I write, but I’ve spent years building the
|| die
habit to the point where I don’t even think about it as I’m writing. I’ll probably edit my post to be a little less absolute, now that I’m awake and have some caffeine in me.One other benefit I forgot to mention to explicit error handling is that you get to actually log a useful error message. Being able to
rg 'failed to scrozzle foo.* because service y was not available'
and immediately find the exact line in the script that failed is so nice. It’s not quite a stack trace with line numbers, but it’s much nicer than what you have with bash by default or with set -e.
I’ve been meaning to learn how to avoid using pipefail, thanks for the info!
Yup, and
set -e
can be used as a try/catch in a pinch (but your way is cleaner)I was tempted for years to use it as an occasional try/catch, but learning Go made me realize that exceptions are amazing and I miss them, but that it is possible (but occasionally hideously tedious) to write software without them. Like, I feel like anyone who has written Go competently (i.e. they handle every returned
err
on an individual or aggregated basis) should be able to write relatively error-handled shell. There are still the billion other footguns built directly into bash that will destroy hopes and dreams, but handling errors isn’t too bad if you just have a littledie
function and the determination to use it.“There are still the billion other footguns built directly into bash that will destroy hopes and dreams, but”
That’s well put. I might put that at the start of all of my future comments about
bash
in the future.Yep. Bash was my first programming language so I have absolutely stepped on every single one of those goddamn pedblasters. I love it, but I also hate it, and I am still drawn to using it.
I didn’t know the locale part…
I learned about it the hard way lol.
seq
used to generate a csv file in a script. My polish friend runs said script, and suddenly there’s an extra column in the csv…I had os-prober fail if locale was Turkish, the seperator thing could explain that.
Shell is great, but if you’re using it as a programming language then you’re going to have a bad time. It’s great for scripting, but if you find yourself actually programming in it then save yourself the headache and use an actual language!
Your scientists were so preoccupied with whether they could, they didn’t stop to think if they should
Honestly, the fact that bash exposes low level networking primitives like a TCP socket via /dev/TCP is such a godsend. I’ve written an HTTP client in Bash before when I needed to get some data off of a box that had a fucked up filesystem and only had an emergency shell. I would have been totally fucked without /dev/tcp, so I’m glad things like it exist.
EDIT: oh, the article author is just using netcat, not doing it all in pure bash. That’s a more practical choice, although it’s way less fun and cursed.
EDIT: here’s a webserver written entirely in bash. No netcat, just the /bin/bash binary https://github.com/dzove855/Bash-web-server
So what IS the difference between scripting and programming in your view?
No clear line, but to me a script is tying together other programs that you run, those programs themselves are the programs. I guess it’s a matter of how complex the logic is too.
The few times I’ve used shell for programming it was in strict work environments where anything compiled was not allowed without a ton of red tape.
Wouldn’t something interpreted like python be a better solution?
For more complicated input/output file handling, certainly.
Little shell scripts do great though if all you need to do is concatenate files by piping them.
It’s like the Internet, it’s not one big truck but a series of tubes.
Yep, in my mind piping together other commands is scripting not programming, exactly what shell scripts are for!
With enough regex and sed/awk you might be able to make even complicated stuff work. I’m not a regex guru (but I do occasionally dabble in the dark arts).
Alpine linux, one of the most popular distros to use inside docker containers (and arguably good for desktop, servers, and embedded) is held together by shell scripts, and it’s doing just fine. The installer, helper commands, and init scripts are all written for busybox sh. But I guess that falls under “scripting” by your definition.
Aka busybox in disguise 🥸
I feel attacked. https://github.com/fmstrat/gam
A lot of people call
set -euo pipefail
the “strict mode” for bash programming, as a reference toin JavaScript. ;
In other words, always add this if you want to stay sane unless you’re a shellcheck user.
People call
set -euo pipefail
strict mode but, it’s just another footgun in a language full of footguns. Shellcheck is a fucking blessing from heaven though. I wish I could forcibly install it on every developer’s system.
I have written 5 shell scripts ever, and only 1 of them has been more complex than “I want to alias this single command”
I can’t imagine being an actual shell dev
It really isn’t bad especially if you use ash
only 1 of them has been more complex than “I want to alias this single command”
I have some literal shell aliases that took me hours to debug…
I do not envy you.
Nah, it’s in the past.
But people, if you are writing a command that detects a terminal to decide to color its output or not, please add some overriding parameters to it.
#!/usr/bin/python
No, sorry. I’m a python dev and I love python, but there’s no way I’m using it for scripting. Trying to use python as a shell language just has you passing data across
Popen
calls with a sea of.decode
and.encode
. You’re doing the same stuff you would be doing in shell, but with a less concise syntax. Literally all of python’s benefits (classes, types, lists) are negated because all of the tools you’re using when writing scripts are processing raw text anyway. Not to mention the version incompatibility thing. You use an f-string in a spicy way once, and suddenly your “script” is incompatible with half of all python installations out there, which is made worse by the fact that almost every distro has a very narrow selection of python versions available on their package manager. With shell you have the least common denominator of posix sh. With Python, some distros rush ahead to the latest release, while other hang on to ancient versions. Evenprint("hello world")
isn’t guaranteed to work, since some LTS ubuntu versions still havepython
pointing to python2.The quickest cure for thinking that Python “solves” the problems of shell is to first learn good practices of shell, and then trying to port an existing shell script to python. That’ll change your opinion quickly enough.
I’m glad powershell is cross-platform nowadays. It’s a bit saner.
Better would be to leave the 1970s and never interact with a terminal again…
What about embedded work? You gonna run a full graphical GUI on a network router?
Quick, how do I do
for i in $(find . -iname '*.pdf' -mtime -30); do convert -density 300 ${i} ${i}.jpeg; done
in a GUI, again?$time = (get-date).adddays(-30) gci -file -filter *.pdf ` | ? { $_.lastwritetime -gt $time } ` | % { convert -density 300 $_.fullname $($_.fullname + ".jpg") }
🤷
What else are you going to do, though?
If you have some particular and complicated task then sure you’d probably write a program for it in a specific high-level language. But that isn’t what the shell is for.
If you’ve already got a bunch of apps and utilities and want to orchestrate them together to do a task, that’s a good shell use case.
Or if you have a system that needs setup and install tasks doing on it to prepare for running your actual workload, that’s also a task which the shell is ideally suited to.
Shell scripting always has a place, and I can’t see it being made obsolete any time soon.
People keep on telling me that python is a “scripting language” but honestly I would rather use the shoddiest and most barebones shell you would give me than python if I had to make a script. It all boils to interfaces, and there are more programs, libraries, and daemons that have a shell interface as opposed to whatever other “better” language there is out there. Trying to write scripts with Python or ruby or whatever will just boils down to plumbing data between external programs in a less succinct syntax. What good is type safety, try/catch, and classes if all the tools that you’re using are taking in and spitting out raw text anyway?
I’m a former (long long ago) Linux admin and a current heavy (but not really deep) powershell user.
The .net-ification of *nix just seems bonkers to me.
Does it really work that well?
The .net-ification of *nix just seems bonkers to me.
It IS bonkers. As a case study, compare the process of setting up a self-hosted runner in gitlab vs github.
Gitlab does everything The Linux Way. You spin up a slim docker container based on Alpine, pass it the API key, and you’re done. Nice and simple.
Github, being owned by Microsoft, does everything The Microsoft way. The documentation mentions nothing of containers, you’re just meant to run the runner natively, essentially giving Microsoft and anyone else in the repo a reverse shell into your machine. Lovely. Microsoft then somehow managed to make their runner software (reminder: whose entire job consists of pulling a git repo, parsing a yaml file, and running some shell commands) depend on fucking dotnet and a bunch of other bullshit. You’re meant to install it using a shitty
setup.sh
script that does that stupid thing with detecting what distro you’re on and calling the native package manager to install dependencies. Which of course doesn’t work for shit for anyone who’s not on debain or fedora because those are the only distro’s they’ve bothered with. So you’re either stuck setting up dotnet on your system, or trying to manually banish this unholy abomination into a docker container, which is gonna end up twice the size of gitlab’s pre-made Alpine container thanks to needing glibc to run dotnet (and also full gnu coreutils for some fucking reason)Bloat is just microsoft’s way of doing things. They see unused resources, and they want to use them. Keep microsoft out of linux.
What type of .net-ification occurs on *nix? I am current linux “admin” and there is close to 0 times where I’ve seen powershell not on windows. Maybe in some microsoft specific hell-scape it is more common, but it’s hard to imagine that there are people that can accept a “shell” that takes 5-10 seconds to start. There are apps written in c# but they aren’t all that common?
I honestly don’t know but there must some translation happening between .net objects and *nix.
And .net “core” started supporting Linux like a decade ago. I’m guessing they’re related ¯\_(ツ)_/¯
I usually only use the terminal when I don’t find an alternative, but powershell usually feels a bit saner than bash.
I’ve also tried nushell, also nice, but in a few situations powershell despite usually being verbose was more “elegant”.
Better would be to leave the 1970s and never interact with a terminal again…
I’m still waiting for someone to come up with a better alternative. And once someone does come up with something better, it will be another few decades of waiting for it to catch on. Terminal emulation is dumb and weird, but there’s just no better solution that’s also compatible with existing software. Just look at any IDE as an example: visual studio, code blocks, whatever. Thousands of hours put into making all those fancy buttons menus and GUIs, and still the only feature that is worth using is the built-in terminal emulator which you can use to run a real text editor like vim or emacs.