https://stackoverflow.com/questions/12498304/using-bash-to-d...
I think appending an explicit || true for commands that are ok to fail makes more sense. Having state you need to keep track of just makes things less readable.
One rule I like, is to ensure that, as well as validation, all validated information is dumped in a convenient format prior to running the rest of the script.
This is super helpful, assuming that some downstream process will need pathnames, or some other detail of the process just executed.
I'll probably also combine a few git commands for every commit and push.
I also use VMs (qemu microvms) based on docker images for development.
I asked ChatGPT to write it and double checked btw.
if [ -x "$(command -v gtimeout)" ]; then
if [ -x "$(command -v gtimeout)" ]; then
if command -v gtimeout >/dev/null; then
The superficial reason the second is "preferred" is that it's slightly better performance wise. Not a huge difference, but it is a difference.
However the hidden, and probably more impactful reason it's preferred, is that the first can give a false negative. If the thing you want to test before calling is implemented as a shell builtin, it will fail, because the `-x` mode of `test` (and thus `[`) is a file test, whereas the return value of `command -v` is whether or not the command can be invoked.
https://dave.autonoma.ca/blog/2019/05/22/typesetting-markdow...
In effect, create a list of dependencies and arguments:
#!/usr/bin/env bash
source $HOME/bin/build-template
DEPENDENCIES=(
"gradle,https://gradle.org"
"warp-packer,https://github.com/Reisz/warp/releases"
"linux-x64.warp-packer,https://github.com/dgiagio/warp/releases"
"osslsigncode,https://www.winehq.org"
)
ARGUMENTS+=(
"a,arch,Target operating system architecture (amd64)"
"o,os,Target operating system (linux, windows, macos)"
"u,update,Java update version number (${ARG_JAVA_UPDATE})"
"v,version,Full Java version (${ARG_JAVA_VERSION})"
)
https://gitlab.com/DaveJarvis/KeenWrite/-/blob/main/scripts/...
Further, the same command-line arguments list can be used to parse the options:
https://gitlab.com/DaveJarvis/KeenWrite/-/blob/main/scripts/...
If you want further generalization, it's possible to have the template parse the command-line arguments automatically for any particular script. Tweak the arguments list slightly by prefixing the name of the variable to assign to the option value provided on the CLI:
ARGUMENTS+=(
"ARG_JAVA_ARCH,a,arch,Target operating system architecture (amd64)"
"ARG_JAVA_OS,o,os,Target operating system (linux, windows, macos)"
"ARG_JAVA_UPDATE,u,update,Java update version number (${ARG_JAVA_UPDATE})"
"ARG_JAVA_VERSION,v,version,Full Java version (${ARG_JAVA_VERSION})"
)
That said, I use Glow to render markdown sometimes. When and how does it connect to internet servers?
https://github.com/charmbracelet/glow/issues/615
But it looks like they finally removed that code a few months ago: https://github.com/charmbracelet/glow/pull/619
I'm fine with it
command -v tput &>/dev/null && [ -t 1 ] && [ -z "${NO_COLOR:-}" ] || tput() { true; }
This little snippet of setup lets you sprinkle tput invocations through your script knowing that it's going to do the right thing in any situation.
if [ -t 1 ] && [ -z "${NO_COLOR:-}" ]; then
COLOR_RESET='[0m'
COLOR_RED='[31m'
COLOR_GREEN='[32m'
COLOR_BLUE='[34m'
else
COLOR_RESET=''
COLOR_RED=''
COLOR_GREEN=''
COLOR_BLUE=''
fi
Be aware there's an escape character at the start of each of color string, which is the POSIX equivalent of $'\e'; Hacker News seems to cut out that escape character.
RED=$(tput setaf 1)
GREEN=$(tput setaf 2)
RESET=$(tput sgr0)It ticks so many boxes:
* Printing non-output information to stdout (usage information is not normal program output, use stderr instead)
* Using copious amounts of colours everywhere to draw attention to error messages.
* ... Because you've flooded my screen with even larger amount of irrelevant noise which I don't care about (what is being ran).
* Coming up with a completely custom and never before seen way of describing the necessary options and arguments for a program.
* Trying to auto-detect the operating system instead of just documenting the non-standard dependencies and providing a way to override them (inevitably extremely fragile and makes the end-user experience worse). If you are going to implement automatic fallbacks, at least provide a warning to the end user.
* ... All because you've tried to implement a "helpful" (but unnecessary) feature of a timeout which the person using your script could have handled themselves instead.
* pipefail when nothing is being piped (pipefail is not a "fix" it is an option, whether it is appropriate is dependant on the pipeline, it's not something you should be blanket applying to your codebase)
* Spamming output in the current directory without me specifying where you should put it or expecting it to even happen.
* Using set -e without understanding how it works (and where it doesn't work).
On the scale of care, “the script can blow up in surprising ways” severely outweighs “error messages are in red.” Also, as someone else pointed out, what if I’m redirecting to a file?
Here’s a script that uses real language things like a function and error checking, but which also prints “oh no”:
set -e
f() {
false
echo oh
}
if f
then
echo no
fi
In terms of sh enlightenment, one of the steps before getting to the above is realizing that every time you use “;” you are using a technique to jam a multi-line expression onto a single line. It starts to feel incongruous to mix single line and multi line syntax:
# weird
if foo; then
bar
fi
# ahah
if foo
then
bar
fi
Shell scripting has its place. Command invocation with sh along with C functions is the de-facto API in Linux. Shell scripts need to fail fast and hard though and leave it up to the caller (either a different language, or another shell script) to figure out how to handle errors.
https://github.com/containerd/nerdctl/blob/main/extras/rootl...
I have since copied this pattern for many scripts: logging functions, grouping all global vars and constants at the top and creating subcommands using shift.
if [ "$(uname -s)" == "Linux” ]; then
stuff-goes-here
else # Assume MacOS
Though for that snippet I would argue for testing for the command rather than the OS (unless Macs or some other common arrangement has something incompatible in the standard path with the same command name?).
For rarely run scripts, consider checking if required flags are missing and query for user input, for example:
[[ -z "$filename" ]] && printf "Enter filename to edit: " && read filename
if that's a script that's run very rarely or once, entering the fields sequentially could also save time, compared to common `try to remember flags -> error -> check help -> success` flow.
Use a better programming language. Go, Typescript, Rust, Python, and even Perl come to mind.
Instead, just check $? and whether a pipe's output has returned anything at all ([ -z "$FOO" ]) or if it looks similar to what you expect. This is good enough for 99% of scripts and allows you to fail gracefully or even just keep going despite the error (which is good enough for 99.99% of cases). You can also still check intermediate pipe return status from PIPESTATUS and handle those errors gracefully too.
SCRIPT_DIR=$( cd -- "$( dirname -- "${BASH_SOURCE[0]}" )" &> /dev/null && pwd )
This is based on this SA's answer: https://stackoverflow.com/questions/59895/how-do-i-get-the-d...
I never got why Bash doesn't have a reliable "this file's path" feature and why people always take the current working directory for granted!
readonly SCRIPT_SRC="$(dirname "${BASH_SOURCE[${#BASH_SOURCE[@]} - 1]}")"
readonly SCRIPT_DIR="$(cd "${SCRIPT_SRC}" >/dev/null 2>&1 && pwd)"
readonly SCRIPT_NAME=$(basename "$0")script_dir="$(dirname "$(realpath "$0")")"
Hasn't failed me so far and it's easy enough to remember
Validating parameters - a built in declarative feature! E.g.: ValidateNotNullOrEmpty.
Showing progress — also built in, and doesn’t pollute the output stream so you can process returned text AND see progress at the same time. (Write-Progress)
Error handling — Try { } Catch { } Finally { } works just like with proper programming languages.
Platform specific — PowerShell doesn’t rely on a huge collection of non-standard CLI tools for essential functionality. It has built-in portable commands for sorting, filtering, format conversions, and many more. Works the same on Linux and Windows.
Etc…
PS: Another super power that bash users aren’t even aware they’re missing out on is that PowerShell can be embedded into a process as a library (not an external process!!) and used to build an entire GUI that just wraps the CLI commands. This works because the inputs and outputs are strongly typed objects so you can bind UI controls to them trivially. It can also define custom virtual file systems with arbitrary capabilities so you can bind tree navigation controls to your services or whatever. You can “cd” into IIS, Exchange, and SQL and navigate them like they’re a drive. Try that with bash!
Somehow whenever people dance to the Google code conventions tune, I find they adhere to questionable practices. I think people need to realize, that big tech conventions are simply their common debominator, and not especially great rules, that everyone should adopt for themselves.
Or filenames that contain the number zero :D
#!/bin/sh
#
# Usage : popc_unchecked BINARY_STRING
#
# Count number of 1s in BINARY_STRING. Made to demonstrate a use of IFS that
# can bite you if you do not quote all the variables you don't want to split.
len="${#1}"
count() { printf '%s\n' "$((len + 1 - $#))"; }
saved="${IFS}"
IFS=0
count 1${1}1
IFS="${saved}"
# PS: we do not run the code in a subshell because popcount needs to be highly
# performant (≖ ᴗ ≖ )I get and love the idea but I'd consider this implementation an anti-pattern. If the output mimics set -x but isn't doing what that is doing, it can mislead users of the script.
The author could also consider trapping debug to maybe be selective while also making it a little more automatic.
It provides logging facilities with colour usage for the terminal (not for redirecting out to a file) and also decent command line parsing. It uses a great idea to specify the calling parameters in the help/usage information, so it's quick and easy to use and ensures that you have meaningful information about what parameters the script accepts.
Also, please don't write shell scripts without running them through ShellCheck. The shell has so many footguns that can be avoided by correctly following its recommendations.
sh -x $SCRIPT
You can use it as a shebang too:
#!/bin/sh -xI created a small awk util that I used throughout the script to style the output. I found it very convenient. I wonder if something similar already exists.
Some screenshots in the PR: https://github.com/ricomariani/CG-SQL-author/pull/18
Let me know guys if you like it. Any comments appreciated.
function theme() {
! $IS_TTY && cat || awk '
/^([[:space:]]*)SUCCESS:/ { sub("SUCCESS:", " \033[1;32m&"); print; printf "\033[0m"; next }
/^([[:space:]]*)ERROR:/ { sub("ERROR:", " \033[1;31m&"); print; printf "\033[0m"; next }
/^ / { print; next }
/^ / { print "\033[1m" $0 "\033[0m"; next }
/^./ { print "\033[4m" $0 "\033[0m"; next }
{ print }
END { printf "\033[0;0m" }'
}Example usage:
exit_with_help_message() {
local exit_code=$1
cat <<EOF | theme
CQL Playground
Sub-commands:
help
Show this help message
hello
Onboarding checklist — Get ready to use the playground
build-cql-compiler
Rebuild the CQL compiler
cat <<EOF | theme
CQL Playground — Onboarding checklist
Required Dependencies
The CQL compiler
$($cql_compiler_ready && \
echo "SUCCESS: The CQL compiler is ready ($CQL)" || \
echo "ERROR: The CQL compiler was not found. Build it with: $CLI_NAME build-cql-compiler"
)
rm -rf ${VAR}/*
https://github.com/ValveSoftware/steam-for-linux/issues/3671
rm -rf -- "${VAR}"/*The python excerpt is my favorite example:
```
$ irb
irb(main):001:0> exit
$ irb
irb(main):001:0> quit
$ python
>>> exit
Use exit() or Ctrl-D (i.e. EOF) to exit
```
<quote> Ruby accepts both exit and quit to accommodate the programmer’s obvious desire to quit its interactive console. Python, on the other hand, pedantically instructs the programmer how to properly do what’s requested, even though it obviously knows what is meant (since it’s displaying the error message). That’s a pretty clear-cut, albeit small, example of [Principle of Least Surprise]. </quote>
I also recommend you catch if the argument is `-h` or `--help`. A careful user won’t just run a script with no arguments in the hopes it does nothing but print the help.¹
if [[ "${1}" =~ ^(-h|--help)$ ]]
¹ For that reason, I never make a script which runs without an argument. Except if it only prints information without doing anything destructive or that the user might want to undo. Everything else must be called with an argument, even if a dummy one, to ensure intentionality.
python has its place, but it's not without its own portability challenges and sneaky gotchas. I have many times written and tested a python script with (for example) 3.12 only to have a runtime error on a coworker's machine because they have an older python version that doesn't support a language feature that I used.
For small, portable scripts I try to stick to POSIX standards (shellcheck helps with this) instead of bash or python.
For bigger scripts, typically I'll reach for python or Typescript. However, that requires paying the cost of documenting and automating the setup, version detection, etc. and the cost to users for dealing with that extra setup and inevitable issues with it. Compiled languages are the next level, but obviously have their own challenges.
Let's focus on solving this then. Because the number of times that I've had to do surgery on horrible bash files because they were written for some platform and didn't run on mine...
Try running a twenty year old BASH script versus a python programme on a new ARM or RISC-V chip.
Or, try running BASH/python on some ancient AIX hardware.
* #!/bin/bash instead of #!/usr/bin/env bash
* [ instead of [[
* -z instead of actually checking how many arguments you got passed and trusting the end user if they do something weird like pass an empty string to your program
* echo instead of printf
* `print_and_execute sdk install java $DEFAULT_JAVA_VERSION` who asked you to install things?
* `grep -h "^sdk use" "./prepare_$fork.sh" | cut -d' ' -f4 | while read -r version; do` You're seriously grepping shell scripts to determine what things you should install?
* Unquoted variables all over the place.
* Not using mktemp to hold all the temporary files and an exit trap to make sure they're cleaned up in most cases.
Except that'll pick up an old (2006!) (unsupported, I'm guessing) version of bash (3.2.57) on my macbook rather than the useful version (5.2.26) installed by homebrew.
> -z instead of actually checking how many arguments you got
I think that's fine here, though? It's specifically wanting the first argument to be a non-empty string to be interpolated into a filename later. Allowing the user to pass an empty string for a name that has to be non-empty is nonsense in this situation.
> You're seriously grepping shell scripts to determine what things you should install?
How would you arrange it? You have a `prepare_X.sh` script which may need to activate a specific Java SDK (some of them don't) for the test in question and obviously that needs to be installed before the prepare script can be run. I suppose you could centralise it into a JSON file and extract it using something like `jq` but then you lose the "drop the files into the directory to be picked up" convenience (and probably get merge conflicts when two people add their own information to the same file...)
It’s only when things are intended to be reused or have a more generic purpose as a tool that you need them to behave better and in a more standard way.
For better user friendliness, I prefer to have the logging level determined by the value of a variable (e.g. LOG_LEVEL) and then the user can decide whether they want to see every single variable assignment or just a broad outline of what the script is doing.
I was taken back by the "print_and_execute" function - if you want to make a wrapper like that, then maybe a shorter name would be better? (Also, the use of "echo" sets off alarm bells).
This one becomes very apparent when using NixOS where /bin/bash doesn’t exist. The vast majority of bash scripts in the wild won’t run on NixOS out of the box.
Your tone is very dismissive. Instead of criticism all of these could be phrased as suggestions instead. It’s like criticising your junior for being enthusiastic about everything they learned today.
For anyone else not familiar with this term
This made me chuckle.
> Your tone is very dismissive.
I know, but honestly when I see a post on the front page of HN with recommendations on how to do something and the recommendations (and resulting code) are just bad then I can't help myself.
The issue is that trying to phrase things nicely takes more effort than I could genuinely be bothered to put in (never mind the fact I read the whole script).
So instead my aim was to be as neutral sounding as possible, although I agree that the end result was still more dismissive than I would have hoped to achieve.
I think it’s pretty good hygiene to set pipefail in the beginning of every script, even if you end up not using any pipes. And at that point is it that important to go back and remove it only to then have to remember that you removed it once you add a pipe?
Sometimes you should even be using PIPESTATUS instead.
In truth when I find myself writing a large "program" in Bash such that shellcheck is cumbersome it's a good indication that it should instead be written in a compiled language.
For the false positives, just put in the appropriate comment to disable ShellCheck's error ahead of that line e.g.
# shellcheck disable=SC2034,SC2015
That stops the warning and also documents that you've used ShellCheck, seen the specific warning and know that it's not relevant to you.
As others have pointed out, you can tune shellcheck / ignore certain warnings, if they’re truly noise to you. Personally, I view it like mypy: if it yells at me, I’ve probably at the very least gone against a best practice (like reusing a variable name for something different). Sometimes, I’m fine with that, and I direct it to be ignored, but at least I’ve been forced to think about it.
I don't think LOC is the correct criterion.
I do solve many problems with bash and I enjoy the simplicity of shell coding. I even have long bash scripts. But I do agree that shell scripting is the right solution only if
= you can solve the problem quickly
= you don't need data structures
= you don't need math
= you don't need concurrencySometimes options are limited to what you know already.
You mean, the complexity of shell coding? Any operation that in a regular language is like foo.method(arg) in shell expands into something like ${foo#/&$arg#%} or `tool1 \`tool2 "${foo}"\` bar | xargs -0 baz`.
Meanwhile, 10 year old Bash scripts I've written still run unmodified.
Winner by a mile (from a software-longevity and low-maintenance perspective at least): Bash
Compare a Python script to a Bash script. If your Python3 script (assuming no dependencies) doesn't work after 6 months I got some questions for you.
(And I don't really get how a 6 month old Python _project_ is likely to fail. I guess I'm just good at managing my dependencies?)
Bun has similar features: https://bun.sh/docs/runtime/shell
Oh? I don't observe this behavior in my testing. Could you share an example? AFAIK, if you don't capture stderr, that should be passed to the user.
> "Instead, just check $? and..."
I agree that careful error handling is ideal. However, IMO it's good defensive practice to start scripts with "-e" and pipefail.
For many/most scripts, it's preferable to fail with inadequate output than to "succeed" but not perform the actions expected by the caller.
$ date +%w
0
$ cat foo.sh
#!/usr/bin/env sh
set -x
set -eu -o pipefail
echo "start of script"
echo "start of pipe" | cat | false | cat | cat
if [ "$(date +%w)" = "0" ] ; then
echo "It's sunday! Here we do something important!"
fi
$ sh foo.sh
+ set -eu -o pipefail
+ echo 'start of script'
start of script
+ echo 'start of pipe'
+ cat
+ false
+ cat
+ cat
$
If you later find out the script has been failing, and find this output, you can guess the pipe failed (it doesn't actually say it failed), but you don't know what part of the pipe failed or why. And you only know this much because tracing was enabled.
If tracing is disabled (the default for most people), you would have only seen 'start of script' and then the program returning. Would have looked totally normal, and you'd be none the wiser unless whatever was running this script was also checking its return status and blaring a warning if it exited non-zero, and then you have an investigation to begin with no details.
> IMO it's good defensive practice to start scripts with "-e" and pipefail.
If by "defensive" you mean "creating unexpected failures and you won't know where in your script the failure happened or why", then I don't like defensive practice.
I cannot remember a single instance in 20 years where pipefail helped me. But plenty of times where I spent hours trying to figure out where a script was crashing and why, long after it had been crashing for weeks/months, unbeknownst to me. To be sure, there were reasons why the pipe failed, but in almost all cases it didn't matter, because either I got the output I needed or didn't.
> it's preferable to fail with inadequate output than to "succeed" but not perform the actions expected by the caller.
I can't disagree more. You can "succeed" and still detect problems and handle them or exit gracefully. Failing with no explanation just wastes everybody's time.
Furthermore, this is the kind of practice in backend and web development that keeps causing web apps to stop working, but the user gets no notification whatsoever, and so can't report an error, much less even know an error is happening. I've had this happen to me a half dozen times in the past month, from a bank's website, from a consumer goods company's website, even from a government website. Luckily I am a software engineer and know how to trace backend network calls, so I could discover what was going on; no normal user can do that.
But interactively, I much prefer Unix shells over PowerShell. When you don't have edge cases and user input validation to deal with, these quirks become much more manageable. Maybe I am lacking experience, but I find PowerShell uncomfortable to use, and I don't know if it has all these fancy interactive features many Unix shell have nowadays.
What you are saying essentially is that PowerShell is a better programming language than bash, quite a low bar actually. But then you have to compare it to real programming languages, like Perl or Python.
Perl has many shell-like features, the best regex support of any language, which is useful when everything is text, many powerful features, and an extensive ecosystem.
Python is less shell-like but is one of the most popular languages today, with a huge ecosystem, clean code, and pretty good two-way integration, which mean you can not only run Python from your executable, but Python can call it back.
If what you are for is portability and built-in commands, then the competition is Busybox, a ~1MB self-contained executable providing the most common Unix commands and a shell, very popular for embedded systems.
In some sense, yes, but there is no distinct boundary. Or at least, there ought not to be one!
A criticism a lot of people (including me) had of Windows in the NT4 and 2000 days was that there was an enormous gap between click-ops and heavyweight automation using C++ and COM objects (or even VBScript or VB6 for that matter). There wasn't an interactive shell that smoothly bridged these worlds.
That's why many Linux users just assumed that Windows has no automation capability at all: They started with click-ops, never got past the gaping chasm, and just weren't aware that there was anything on the other side. There was, it just wasn't discoverable unless you were already an experienced developer.
PowerShell bridges that gap, extending quite a bit in both directions.
For example, I can use C# to write a PowerShell module that has the full power of a "proper" programming language, IDE with debug, etc... but still inherits the PS pipeline scaffolding so I don't have to reinvent the wheel for parameter parsing, tab-complete, output formatting, etc...
Wait! The fact that arguments with a leading hyphen are interpreted as options is not bash's fault. It's ingrained in the convention of UNIX tools and there's nothing bash can do to mitigate it. You would have the same problem if you got rid of any shell and directly invoked commands from Python or C.
Re: non-standard tools, if you’re referring to timeout, that’s part of GNU coreutils. It’s pretty standard for Linux. BSDs also have it from what I can tell, so it’s probably a Mac-ism. In any case, you could just pipe through sleep to achieve the same thing.
> …inputs and outputs are strongly typed objects
And herein is the difference. *nix-land has everything as a file. It’s the universal communication standard, and it’s extremely unlikely to change. I have zero desire to navigate a DB as though it were a mount point, and I’m unsure why you would ever want to. Surely SQL Server has a CLI tool like MySQL and Postgres.
You just said everything “is a file” and then dismissed out of hand a system that takes that abstraction even further!
PowerShell is more UNIX than UNIX!
Pythonistas who are used to __dir__ and help() would find themselves comfortable with `gm` (get-member) and get-help to introspect commands.
You will also find Python-style dynamic typing, except with PHP syntax. $a=1; $b=2; $a + $b works in a sane manner (try that with bash). There are still funny business with type coercion. $a=1; $b="2"; $a+$b (3); $b+$a ("21");
I also found "get-command" very helpful with locating related commands. For instance "get-command -noun file" returns all the "verb-noun" commands that has the noun "file". (It gives "out-file" and "unblock-file")
Another nice thing about powershell is you can retain all your printf debugging when you are done. Using "Write-Verbose" and "Write-Debug" etc allows you to write at different log levels.
Once you are used to basic powershell, there are bunch of standard patterns like how to do Dry-Runs, and Confirmation levels. Powershell also supports closures, so people create `make` style build systems and unit test suites with them.
I'm not a fan of powershell myself as the only time I've tried it (I don't do much with Windows), I hit a problem with it (or the object I was using) not being able to handle more than 256 characters for a directory and file. That meant that I just installed cygwin and used a BASH script instead.
PowerShell blows bash out of the water. I love it.
If I wanted the features that pwsh brings I would much rather just pick a language like Golang or Python where the experience is better and those things will work on any system imaginable. Whereas pwsh is really good on windows for specifically administrative tasks.
Both of them should be simply python and typescript compatible dlls.
You can “cd” into IIS, Exchange, and SQL and navigate them like they’re a drive. Try that with bash!
This exists.
PowerShell can be embedded into a process as a library... and used to build an entire GUI that just wraps the CLI commands.
The .NET library for this is System.Management.Automation.
You can call a PowerShell pipeline with one line of code: https://learn.microsoft.com/en-us/dotnet/api/system.manageme...
Unlike invoking bash (or whatever) as a process, this is much lighter weight and returns a sequence of objects with properties. You can trivially bind those to UI controls such as data tables.
Similarly the virtual file system providers expose metadata programmatically such as “available operations”, all of which adhere to uniform interfaces. You can write a generic UI once for copy, paste, expand folder, etc and turn them on or off as needed to show only what’s available at each hierarchy level.
As an example, the Citrix management consoles all work like this. Anything you can do in the GUI you can do in the CLI by definition because the GUI is just some widgets driving the same CLI code.
fish, Python, and oilshell (ysh) are ultimately on better footing.
Still I’ve always used Ctrl+D, which works everywhere unixy.
Python might be surprising, but in this example, it's only surprising once, and helpful when it surprises you. Now you know quitting requires calling a function and that function is named exit() (although amusingly python3 anyway also accepts quit()). And being fully pedantic it doesn't know what you mean, it is assuming what you mean and making a suggestion, but that's not the same as knowing.
From here on I'm not arguing the point anymore, just recording some of the interesting things I discovered exploring this in response to your comment:
You can do this in python (which IMO is surprising, but in a different way):
```
>>> quit
Use quit() or Ctrl-D (i.e. EOF) to exit
>>> quit=True
>>> quit
True
>>> quit()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'bool' object is not callable
>>> exit()
```
`exit` is a class isntance according to type. So we should be able to create something similar, and indeed we can:
```
>>> class Bar:
... def __repr__(self):
... return "Type bar() to quit!"
... def __call__(self):
... print("I quit!")
...
>>> bar = Bar()
>>> bar
Type bar() to quit!
>>> bar()
I quit!
>>>
```
```
>>> class SuperExit:
... def __init__(self, real):
... self.real_exit=real
... def __repr__(self):
... print("Exiting via repr")
... self.real_exit()
... def __call__(self):
... print("Exiting via call")
... self.real_exit()
...
>>> exit = SuperExit(exit)
>>> exit
Exiting via repr
```We can include these as well, but each keyword that you include brings diminishing returns at the cost of clutter and inconsistence in the API. Python problematically decides that returns diminish after the first --- “first” according to developers, that is --- possibility in all cases. Ruby anticipates that everyone's first choice will be different and practically maximizes comfort of users.
The proliferation of Python has only made my feelings worse. Try running a 6 month old Python project that you haven't touched and see if it still runs. /eyeroll
My experience has been 6 month of python works fine. In fact, python is my go to these days for anything longer than a 5 line shell script (mostly because argparse is builtin now). On the other hand, running a newly written python script with a 6 month old version of python, that's likely to get you into trouble.
I’ve seen more than enough code from folks with combative takes to know “[their] shit don’t shine” either.
If your goal is improvement instead of venting you don’t want to use those.
There's over 1000 open issues on the GitHub repo, and over 100 contain "false positive". I recognize several of these at first glance.
https://github.com/koalaman/shellcheck/issues?q=is%3Aissue+i...
The biggest leap for automation on Windows has been WSL, aka shipping Linux.
It’s not so much about error handling. It’s more about not executing all sorts of stuff after something fails.
I know that this is probably beyond bash scripting vs python scripting but I was just replying to how 6 months project can have problems.
Also not a 6 months scale but the python standard library definitely changes and I would take bash anytime if I have to use venv for running util scripts.
Edit: When python3.8 removed 'time.clock()' it was annoying to change that. I know that it was deprecated since 3.3 (as I remember) but this is the example I have in mind now. But probably it was before I was born that people using
start=$(date +%s%N)
end=$(date +%s%N)
And I will be dead before/if this becomes impossible to use.
Yes it did, by having a non-zero exit code. However, it didn't explicitly mention that it didn't complete successfully, but that's down to the script writer. I like to include a function to tidy up temporary files etc. when the script exits (e.g. trap __cleanup_before_exit EXIT) and it's easy to also assign a function to run when ERR is triggered - if you wish, you can set it to always provide an error backtrace.
but yea, shell is foremost a composition language/environment
"I can't help myself" is not a valid excuse. If you seriously cannot bother to phrase things less dismissively, then you shouldn't comment in the first place.
One of the best guidelines established for HN, is that you should always be kind. It's corny and obvious, and brings to mind the over-said platitude my mom, and a million other moms, used to say: "if you don't have anything nice to say, don't say anything at all."
Your concession was admirable, but your explanation leads me to think that you misunderstand the role you play in the comments. You are not supposed to be a reaction bot; HN is not the journal for your unfiltered thoughts and opinions.
Despite how easy it would be, you cannot and must not simply write replies. Absolutely everything (yes, everything) written here should assume the best, and be in good faith. Authors and the community deserve that much.
This goes for other sites as well, but especially for a community that strives for intellectual growth, like Hacker News.
Apologies if I sounded harsh.
I don't agree that I have any responsibilities on the internet. (edit: Outside of ones I come up with.)
> One of the best guidelines established for HN, is that you should always be kind.
Kindness is subjective, I was not trying to be actively unkind. It's just that the more you attempt to appear kind across every possible metric the more difficult and time consuming it is to write something. I had already put in a lot of effort to read the article, analyse the code within it, and analyse the code behind it. You have to stop at some point, and inevitably someone out there will still find what you wrote to be unkind. I just decided to stop earlier than I would if I was writing a blog post.
> "if you don't have anything nice to say, don't say anything at all."
This is not a useful adage to live by. If you pay someone to fix your plumbing and they make it worse, certainly this won't help you. Likewise, If people post bad advice on a website lots of people frequent and nobody challenges it, lots of people without the experience necessary to know better will read it and be influenced by it.
> You are not supposed to be a reaction bot; HN is not the journal for your unfiltered thoughts and opinions.
I think it's unkind to call what I wrote an unfiltered thought/opinion/reaction. You should respect that it:
* Takes a lot of time and experience before you can make these kinds of remarks
* Takes effort to read the post, evaluate what is written in it, write a response, and verify you are being fair and accurate.
* Takes even more effort to then read the entire script, and perform a code review.
If I had looked at the title and headlines and written "This is shit, please don't read it." then I think you would have a point but I didn't do that.
More to the point, a substantial number of people seem to have felt this was useful information and upvoted both the comments.
> Despite how easy it would be, you cannot and must not simply write replies. Absolutely everything (yes, everything) written here should assume the best, and be in good faith. Authors and the community deserve that much.
I prefaced my first comment by pointing out that the people who make the mistakes I outlined are usually well meaning. My critique was concise and could be seen as cold but it was not written in bad faith.
Note what you just said: when you want an object with a method that takes a parameter, you find bash too complex.
You gave an example that is not appropriate for bash.
However, bash does have functions. So if you don't need an entire underlying object system just to run your logic, you could have
function foomethod () {
parm1=$1
#more logic
}Be damned the day I decided to write a set of scripts in it rather than looking for a way to make typescript my daily driver, like it is now. Bash “code” “base” is one of the worst programming jokes.
One of GP arguments in favor of PowerShell is that most commands are builtin, so this problem can be solved by the shell itself, and furthermore, it is based on strongly typed objects, which should make it clear what is a file and what is a command line option. And I think he has a point. Regular command line parsing is a mess on Windows though.
In "real" programming languages, library APIs are usually favored over command lines, and they are usually designed in such a way that options and file arguments are distinct. You may still need to run commands at some point, but you are not reliant on them for every detail, which, in traditional shell scripting includes trivial things like "echo", "true", "false", "test", etc... Now usually builtin.
As for bash "doing something about it", it would greatly benefit from a linter. I know they exist, but I don't know if it is standard practice to use them.
A better system shell could make it easy to define shims for the existing programs. Also it could make their calling easier, e.g. with named arguments. So when you wanted to delete your file called -rf, you would say
rm(file="-rf")
Let's analyze your example with 'rm': it works as long as 'rm' is an internal routine. If it's an external program, independently of the syntax you use to specify the arguments, sooner or later the shell will need to actually call the 'rm' executable, and to pass '-rf' to it as argument number 1. The 'rm' executable will then examine its arguments, see that the first one begins with a hyphen and interpret it as an option.
As I said, the only way to avoid all this would be to replace 'rm' with an internal routine. Then you would replace 'cp' and 'ln', and what else? Of course 'echo' and 'printf', 'cat', 'ls', 'cd' maybe, why not 'find' and 'grep'? What about 'head', 'tail', 'cut'? Don't forget 'sed' and 'awk'... the list is getting longer and longer. Where do you draw the line?
Seriously, the only mitigation would be to define a function to 'sanitize' an argument to make it appear as a file if used as an argument to an external program. Something like:
force_file() {
case "$1" in
-*) echo "./$1" ;;
*) echo "$1" ;;
esacThis doesn't work with 'echo' though.
Eh, that feels pretty arbitrary to me. `quit()` and `exit()` both work, and looking at other languages, `exit()` should almost certainly be your first choice
C: exit(int)
Java: System.exit(int)
SBCL: (quit)/(exit)
C#: Environment.Exit(int)
PHP: exit(int)/exit(string)
Rust: std::process::exit(int)
In ruby, parentheses are optional for function calls. `exit` is a regular call, not some REPL peculiarity.
EDIT: Nevermind. Just found that despite the `exit` method being already defined, both irb and pry overshadow that with a repl command that does the same thing. Maybe it's so that it can't be redefined.
Have a look at https://mywiki.wooledge.org/BashPitfalls#echo_.24foo
Most of the time, "echo" works as you'd expect, but as it doesn't accept "--" to signify the end of options (which is worth using wherever you can in scripts), it'll have problems with variables that start with a dash as it'll interpret it as an option to "echo" instead.
It's a niche problem, but replacing it with "printf" is so much more flexible, useful and robust. (My favourite trick is using "printf" to also replace the "date" command).
Also, here's some more info on subtle differences between "echo" on different platforms: https://unix.stackexchange.com/questions/65803/why-is-printf...
This is Stockholm Syndrome.
You’ve internalised your limitations and have grown to like them.
What I’m saying is that in *nix tooling, things are typically designed to do one thing well. So no, I don’t want my shell to also have to talk MySQL, Postgres, SQL Server, DB2, HTTP, FTP, SMTP…
What's the point of the shell, if not to manage your databases, your REST APIs, files, and mail? Is it something you use for playing games on, or just for fun?
> designed to do one thing well.
Eeexcept that this is not actually true in practice, because the abstraction was set at a level that's too low. Shoving everything into a character (or byte) stream turned out to be a mistake. It means every "one thing" command is actually one thing plus a parser and and encoder. It means that "ps" has a built-in sort command, as do most other UNIX standard utilities, but they all do it differently. This also means that you just "need to know" how to convince each and every command to output machine-readable formats that other tools on the pipeline can pick up safely.
I'll tell you a real troublshooting story, maybe that'll help paint a picture:
I got called out to assist with an issue with a load balancer appliance used in front of a bunch of Linux servers. It was mostly working according to the customer, but their reporting tool was showing that it was sending traffic to the "wrong" services on each server.
The monitoring tool used 'netstat' to track TCP connections, which had a bug in that version of RedHat where it would truncate the last decimal digit of the port number if the address:port combo had the maximum possible number of digits, e.g.: 123.123.123.123:54321 was shown as 123.123.123.123:5432 instead.
Their tool was just ingesting that pretty printed table intended for humans with "aligned" columns, throwing away the whitespace, and putting that into a database!
This gives me the icks, but apparently Just The Way Things Are Done in the UNIX world.
In PowerShell, Get-NetTCPConnection outputs objects, so this kind of error is basically impossible. Downstream tools aren't parsing a text representation of a table or "splitting it into columns", they receive the data pre-parsed with native types and everything.
So for example, this "just works":
Get-NetTCPConnection |
Where-Object State -EQ 'Bound' |
Group-Object LocalPort -NoElement |
Sort-Object Count -Descending -Top 10
This kind of thing is a challenge with UNIX tools, and then is fragile forever. Any change to the output format of netstat breaks scripts in fun and create ways. Silently. In production.
I hope you never have to deal with IPv6.
netstat -aln \
| grep ESTABLISHED \
| awk '{print $4}' \
| grep -Po '\:\d+$' \
| grep -Po '\d+' \
| sort \
| uniq -c \
| sort -r \
| head -n 10
It's for communicating with the operating system, launching commands and viewing their output. And some scripting for repetitive workflows. If I'd want a full programming environment, I'd take a Lisp machine or Smalltalk (a programmable programming environment).
Any other systems that want to be interactive should have their own REPL.
> This kind of thing is a challenge with UNIX tools, and then is fragile forever. Any change to the output format of netstat breaks scripts in fun and create ways. Silently. In production.
The thing is if you're using this kind of scripts in production, then not testing it after updating the system, that's on you. In your story, they'd be better of writing a proper program. IMO, scripts are automating workflows (human guided), not for fire and forget process. Bash and the others deals in text because that's all we can see and write. Objects are for programming languages.
To call other programs to do those things. Why on earth would I want my shell to directly manage any of those things?
I think you're forgetting something: *nix tools are built by a community, PowerShell is built by a company. Much like Apple, Microsoft can insist on and guarantee that their internal API is consistent. *nix tooling cannot (nor would it ever try to) do the same.
> It means that "ps" has a built-in sort command, as do most other UNIX standard utilities, but they all do it differently.
I haven't done an exhaustive search, but I doubt that most *nix tooling has a built-in sort. Generally speaking, they're built on the assumption that you'll pipe output as necessary to other tools.
> This also means that you just "need to know" how to convince each and every command to output machine-readable formats that other tools on the pipeline can pick up safely.
No, you don't, because plaintext output is the lingua franca of *nix tooling. If you build a tool intended for public consumption and it _doesn't_ output in plaintext by default, you're doing it wrong.
Here's a one-liner with GNU awk; you can elide the first `printf` if you don't want headers. Similarly, you can change the output formatting however you want. Or, you could skip that altogether, and pipe the output to `column -t` to let it handle alignment.
netstat -nA inet | gawk -F':' 'NR > 2 { split($2, a, / /); pc[a[1]]++ } END { printf "%-5s %s\n", "PORT", "COUNT"; PROCINFO["sorted_in"]="@val_num_desc"; c=0; for(i in pc) if (c++ < 10) { printf "%-5s %-5s\n", i, pc[i] } }'
PORT COUNT
6808 16
3300 8
6800 6
6802 2
6804 2
6806 2
60190 1
34362 1
34872 1
38716 1
Set the field separator to `:`
Skip the first two lines (because they're informational headers)
Split the 2nd column on space to skip the foreign IP
Store that result in variable `a`
Create and increment array `pc` keyed on the port
When done, do the following
Print a header
Sort numerically, descending
Initialize a counter at 0
For every element in the pc array, until count hits 10, print the value and key
You may look at this and scoff, but really, what is the difference? With yours, I have to learn a bunch of commands, predicates, options, and syntax. With mine, I have to... learn a bunch of commands, predicates, options, and syntax (or just awk ;-)).
> This kind of thing is a challenge with UNIX tools
It's only a challenge if you don't know how to use the tools.
> Any change to the output format of netstat breaks scripts in fun and create ways
The last release of `netstat` was in 2014. *nix tools aren't like JavaScript land; they tend to be extremely stable. Even if they _do_ get releases, if you're using a safe distro in prod (i.e. Debian, RedHat), you're not going to get a surprise update. Finally, the authors and maintainers of such tools are painfully aware that tons of scripts around the world depend on them being consistent, and as such, are highly unlikely to break that.
> Silently. In production.
If you aren't thoroughly testing and validating changes in prod, that's not the fault of the tooling.
With shell, I can take the same tools I’ve already been using as one-liners while fiddling around, and reuse them. There is no syntax mapping to do in my head.
With any other language, I have to map the steps, and probably also add various modules (likely within stdlib, but still). That’s not nothing.
I’ve rewritten a somewhat-complicated bash script into Python. It takes some time, especially when you want to add tests.
I have a rule that if I’m using arrays I should move to Python, PHP, etc. It’s a nice red flag. Arrays in Bash are terrible and a sign that things are getting more complicated.
If that doesn't track with you, that's cool, I'm happy for you.
I find that there's a lot of good information in the comments on HackerNews, so sometimes advice and recommendations aren't just designed for the parent comment.
Your reply adds nothing of value and comes across as being rude - you could have simply ignored my comment if you found it of no value to you.
> If ShellCheck is spitting out lots of warnings, then it'd be worth changing your shell writing style to be more compliant with it.
Is just a very roundabout way of saying ‘If you get a lot of errors using shellcheck you are doing it wrong’, which may or may not be true, but it’d make anyone defensive.
Those mechanisms exist for the inexperienced author (especially in a team setting) where you want some minimum quality and consistency.
An example where Shellcheck might be useful for you is when working with a team of junior programmers. You don't necessarily have the time to teach them the ins and outs of bash, but you can quickly setup Shellcheck to make sure they don't make certain types of errors.
I think your position is totally valid and nobody can or should force you to use a linter, but I think that even for you there _can_ be situations where they might be useful.
I think I'm fairly experienced in shell and Python (~20 and ~8 YOE, respectively), and still find value in linters, type checkers, etc. Maybe moreso in Python, but that's probably a function of me writing larger programs in Python than in shell, and usually changing my mind on something as I'm writing it.
Sure, on Linux, where your only common options bash or "software".
On Windows, with PowerShell, I can don't have to write a software program. I can write a script that reads like a hypothetical C# Shell would, but oriented towards interactive shells.
(Note that there is a CS-Script, but it's a different thing intended for different use-cases.)
I personally setup linters/formatters/other static analysis for solo projects, even for languages I know very well.
I just didn't want to write a comment large enough to capture all of the nuance :)
Personally, I'm fine with BASH arrays (even associative ones) and yes, the syntax can be opaque, but they get the job done. I find that the long-term advantages of BASH outweigh the many, many problems with it. (If you want something to keep running for 20 years on a variety of different machines and architectures, then BASH is easier to manage than almost any other language).
My general rule of thumb is that bash is fine when the equivalent Python would mostly be a whole bunch of `subprocess.run` commands. But as soon as you're trying to do a bunch of logic and you're reaching for functions and conditionals and cases... just break out Python.
call([options.cmake_path,'-G','Visual Studio 16','-A','x64','-S','.','-B',build_folder],check=True)
I also think bun alongside typescript is quite viable, especially with the shell interop:
XONSH is a Python-powered shell
Xonsh is a modern, full-featured and cross-platform shell. The language is a
superset of Python 3.6+ with additional shell primitives that you are used to
from Bash and IPython. It works on all major systems including Linux, OSX, and
Windows. Xonsh is meant for the daily use of experts and novices.
What good is trading away the benefits of bash extensions just to run the script on a homogeneous cluster anyways?
The only remotely relevant alternative operating systems all have the ability to install a modern distribution of bash. Leave POSIX shell in the 1980s where it belongs.
Could you change that by amending your $PATH so that you're preferred version is chosen ahead of the default?
I think the `#!/bin/bash` will always invoke that direct file without searching your $PATH. People say you can do `#!bash` to do a $PATH search but I've just tried that on macOS 15 and an Arch box running a 6.10.3 kernel and neither worked.
That's why env is generally preferred as it finds the appropriate bash for the system.
You two are in violent agreement.
#!/usr/bin/env1. Your script outputs an error when run, because 'bash' itself doesn't have netstat as a built-in. That's an external command. In my WSL2, I had to install it. You can't declaratively require this up-front, you script has to have an explicit check... or it'll just fail half-way through. Or do nothing. Or who knows!?
PowerShell has up-front required prerequisites that you can declare: https://learn.microsoft.com/en-us/powershell/module/microsof...
Not that that's needed, because Get-NetTcpConnection is a built-in command.
3. Your script is very bravely trying to parse output that includes many different protocols, including: tcp, tcp6, udp, udp6, and unix domain sockets. I'm seeing random junk like 'ACC' turn up after the first awk step.
4. Speaking of which, the task was to get tcp connections, not udp, but I'll let this one slide because it's an easy fix.
5. Now imagine putting your script side-by-side with the PowerShell script, and giving it to people to read.
What are the chances that some random person could figure out what each one does?
Would they be able to modify the functionality successfully?
Note that you had to use 'awk', which is a parser, and then three uses of 'grep' -- a regular expression language, which is also a kind of parsing.
The PowerShell version has no parsing at all. That's why it's just 4 pipeline expressions instead of 9 in your bash example.
Literally in every discussion about PowerShell there's some Linux person who's only ever used bash complaining that PS syntax is "weird" or "hard to read". What are they talking about!? It's half the complexity for the same functionality, reads like English, and doesn't need write-only hieroglyphics for parameters.
Heck, just checking between Bash, ZSH and Fish on my local machine here and Bash and ZSH's version is from 2003 and provides a single `-n` option and declares POSIX compliance, but explicitly calls out that `sh`'s version doesn't accept the `-n` argument. Fish provides their own implementation that accepts arguments `[nsEe]` from 2023. Every day I consider it a miracle that most of the wider internet and linux/unix world that underlies so much of it works at all, let alone reliably enough to have multiple nines of uptime. "Worse is better" writ large I guess.
I had an experience recently trying to deploy an agent on a dozen different Linux distros.
I had the lightbulb moment that the only way to run IT in an org using exactly one distro. Ideally one version, two at the most during transitions. Linux is a kernel, not an operating system. There are many Linux operating systems that are only superficially “the same”.
Technically speaking though, there's no reason you couldn't do that all in bash. It's not the shell that's the problem here (at least, to an extent, passing via text I guess is partly a shell problem). There's no reason you couldn't have an application objNetStat that exported JSON objects and another app that filtered those objects, and another that could group them and another that could sort them. Realistically "Sort-Object Count -Descending -Top 10" could be a fancy alias for "sort | uniq -c | sort -r | head -n 10". And if we're not counting flags and arguments to a function as complexity, if we had our hypothetical objNetstat, I can do the whole thing in one step:
objNetstat --json \
| jq -c '[.[] | select(.state == "ESTABLISHED")] | group_by(.port) | map({port:.[0].port, count: map(.host) | length}) | sort_by(.count) | reverse | [limit(10;.[])]'
All joking aside, that's not a bad solution to the underlying problem. Fundamentally, unstructured data in shell pipelines is much of the issue, and JSON can be used to provide that structure. I'm seeing more and more tools emit or accept JSON. If one can pinch their nose and ignore the performance overhead of repeatedly generating and parsing JSON, it's a workable solution.
Years ago, a project idea I was really interested for a while was to try to write a shell in Rust that works more like PowerShell.
Where I got stuck was the fundamentals: PowerShell heavily leans on the managed virtual machine and the shared memory space and typed objects that enables.
Languages like C, C++, and Rust don't really have direct equivalents of this and would have to emulate it, quite literally. At that point you have none of the benefits of Rust and all of the downsides. May as well just use pwsh and be done with it!
Since then I've noticed JSON filling this role of "object exchange" between distinct processes that may not even be written in the same programming language.
I feel like this is going to be a bit like UTF-8 in Linux. Back in the early 2000s, Windows had proper Unicode support with UTF-16, and Linux had only codepages on top of ASCII. Instead of catching up by changing over to UTF-16, Linux adopted UTF-8 which in some ways gave it better Unicode support than Windows. I suspect JSON in the shell will be the same. Eventually there will be a Linux shell where everything is always JSON and it will work just like PowerShell, except it'll support multiple processes in multiple languages and hence leapfrog Windows.
Anyone who's written more than a few scripts for others will have learned to do something like this at the start:
declare -a reqs
reqs+=(foo bar baz)
missing=0
for r in "${reqs[@]}"; do
if (! command -v "$r" &>/dev/null); then
echo "${r} is required, please install it"
missing=1
fi
done
if [ $missing -gt 0 ]; then
exit 1
fi
They probably didn't know you could specify a type. Mine only displays TCP4.
> Now imagine putting your script side-by-side with the PowerShell script, and giving it to people to read.
I'm gonna gatekeep here. If you don't know what that script would do, you have no business administering Linux for pay. I'm not saying that in a "GTFO noob" way, but in a "maybe you should know how to use your job's tools before people depend on you to do so." None of that script is using exotic syntax.
> Note that you had to use 'awk', which is a parser, and then three uses of 'grep' -- a regular expression language, which is also a kind of parsing.
They _chose_ to. You _can_ do it all with awk (see my example in a separate post).
> Literally in every discussion about PowerShell there's some Linux person who's only ever used bash complaining that PS syntax is "weird" or "hard to read". What are they talking about!? It's half the complexity for the same functionality, reads like English, and doesn't need write-only hieroglyphics for parameters.
And yet somehow, bash and its kin continue to absolutely dominate usage.
There is a reason that tools like ripgrep [0] are beloved and readily accepted: they don't require much in the way of learning new syntax; they just do the same job, but faster. You can load your local machine up with all kinds of newer, friendlier tools like fd [1], fzf[2], etc. – I definitely love fzf to death. But you'd better know how to get along without them, because when you're ssh'd onto a server, or god forbid, exec'd into a container built with who-knows-what, you won't have them.
Actually, that last point sparked a memory: what do you do when you're trying to debug a container and it doesn't have things like `ps` available? You iterate through the `/proc` filesystem, because _everything is a file._ THAT is why the *nix way exists, is wonderful, and is unlikely to ever change. There is always a way to get the information you need, even if it's more painful.
[0]: https://github.com/BurntSushi/ripgrep
Oh. Oh! This is a confusing thread. Apologies all!
So this whole conversation and a different one about python and it's behavior around `exit` vs `exit()` sent me down a rabbit hole of seeing if I could make the python interpreter have a "shell like" dsl for piping around data. It turns out you sort of can. I don't think you can defeat the REPL and make a function call like `echo "foo" "bar" "baz", but you can make it do this:
netstat("-ln") | filter_by({"state":"ESTABLISHED"}) \
| group_by(["local_port"]) | count_groups \
| sort("count", descending=True) | limit(10)
Hmmm, if you need that sort of shared memory access throughout the shell, you probably need a language like python (or maybe better Lisp) with a REPL and the ability/intent to self modify while running. Of course, every time you have to farm out because you don't have a re-written replacement internally to the shell app, you'd still parsing strings, but at least you could write a huge part of data processing in the shell language and keep it in house. Years ago I worked for a company that was using Microsoft's TFVC services (before it was azure devops or whatever they call it now) and wrote a frontend to their REST API in python that we could call from various other scripts and not be parsing JSON everywhere. Where this is relevant to the discussion is that one of the things I built in (in part to help with debugging when things went sideways) was an ability to drop into the python REPL mid-program run to poke around at objects and modify them or the various REST calls at will. With well defined functions and well defined objects , the interactive mode was effectively a shell for TFVC and the things we were using.
Though all of that said, even if one did that, they would still either need to solve the "object model" problem for disparate linux tools, or worse commit to writing (or convincing other people to write and maintain) versions of all sorts of various tools in the chosen language to replace the ones the shell isn't farming out to anymore. Its one thing to chose to write a shell, it's something else entirely to choose to re-write the gnu userland tools (and add tools too)
Today's your lucky day!
My experience of ShellCheck is that you only get loads of warnings when you first start out using it and it finds all of your unquoted variables. Once you get more experienced with writing scripts and linting them with ShellCheck, the number of warnings should dramatically reduce, so it seems odd that an experienced script writer would be falling foul of ShellCheck being pedantic about what you're writing.
> ‘If you get a lot of errors using shellcheck you are doing it wrong’
I kind of agree with that, although a lot of ShellCheck's recommendations might not be strictly necessary (you may happen to know that a certain variable will never contain a space), it's such a good habit to get into.
It's not simply being pedantic, it is wrong. Your writing gives the impression that the tool is infallible.
If I was new to writing shell scripts, shellcheck is clearly a wise choice. The language is loaded with footguns. But as someone who has been writing scripts for decades, I already know about all the footguns. My experience with shellcheck is that it mostly finds false positives that waste my time.
I think the huge number of footguns is what makes BASH scripting fun.
Adopting any kind of quality assurance tool is implicitly buying into its "opinionated" worldview. Forfeiting one's autonomy for some person(s) notions of convention.
Rephrased: Using shellcheck is a signal to potential user's, per the Principal of Least Astonishment. No matter if either party doesn't particularly care for shellcheck; it's just a tool to get on the same page more quickly.
e.g. I always put BASH variables in curly braces and double quotes which is often unnecessary (and more verbose), but it means that I don't trigger any ShellCheck warnings for them and it's easier to just type the extra characters than thinking about whether or not they'll actually make any difference.
If it's useful for you, then wonderful!
import os
os.rename(“src.txt”, “dest.txt”)
?Now, show us `mycommand | sed 's/ugly/beautiful/g' | awk -F: '{print $2,$4}' 1> something.report 2> err.log` in Python.
If it became unwieldy you’d turn it into a script:
#!/bin/sh
beautify() {
sed -e ‘
s/ugly/beautiful/g
…other stuff
‘
}
select() {
awk ‘
{print $2, $4}
…other stuff
‘
}
mycommand | beautify | select
from subprocess import Popen, PIPE
CMD = ("printf", "x:hello:67:ugly!\nyy$:bye:5:ugly.\n")
OUT = "something.report"
ERR = "err.log"
def beautify(str_bytes):
return str_bytes.decode().replace("ugly", "beautiful")
def filter(str, \*index):
parts = str.split(":")
return " ".join([parts[i-1] for i in index])
with open(OUT, "w") as out, open(ERR, "w") as err:
proc = Popen(CMD, stdout=PIPE, stderr=err)
for line_bytes in proc.stdout:
out.write(filter(beautify(line_bytes), 2, 4))
Edit: this is proving very difficult to format on mobile, sorry if it's not perfect.
Like.
myvar = `mycommand | sed 's/ugly/beautiful/g' | awk -F: '{print $2,$4}' 1> something.report 2> err.log`
os.system('mycommand | sed 's/ugly/beautiful/g' | awk -F: '{print $2,$4}' 1> something.report 2> err.log')
We have a completely different definition of fun.
I really only use bash when I need to chain a few commands. As soon as there is more complex logic I move to some programming language.
For me, the "line in the sand" is not so much whether something is "safer" in a different language. I often find this to be a bit of a straw-man that stands in for skill issues - though I won't argue that shell does have a deceptively higher barrier to entry. For me, it is whether or not I find myself wanting to write a more robust test suite, since that might be easier to accomplish with Ginkgo or pytest or `#include <yourFavorateTestLibrary.h>`.
But if all I need to do is generate the report I proposed...why would I embed that in a Ruby script (or a Python script, or a Perl script, etc.) when I could just use a bash script?
If your position is that we should not be writing bash but instead Python, then yes, it is absolutely fair.
> the benefit of which is that I can actually read it.
And you couldn't read the command pipeline I put together?
> What happens if you want to retry a line if it fails?
Put the thing you want to do in a function, execute it on a line, if the sub-shell returns a failure status, execute it again. It isn't like bash does not have if-statements or while-loops.
> And you couldn't read the command pipeline I put together?
It took me multiple goes, but the equivalent in python I can understand in one go.
> Put the thing you want to do in a function, execute it on a line, if the sub-shell returns a failure status, execute it again. It isn't like bash does not have if-statements or while-loops.
But when you do that, it all of a sudden looks a lot more like the python code