I am not a huge fan of most of these, but a few do seem useful.
: "${1:?missing argument, aborting!}"
I wouldn't use this because I would want to give $1 a name for the rest of the script, so I would assign. But it can be a nice way to give a clear error for missing required environment variables.
Many of the others (like truncating files) are probably more clearly written with dedicated commands, but may come in useful if you are going to extreme lengths to avoid dependencies outside of the shell.
You are very much correct and I 100% agree with you, I have updated the first example to include a snippet where a proper env-var is used to show of the automatic diagnostic.
"Shortcuts" like :? that tie together two unrelated things (checking a variable for a condition, expanding the value of that variable) drive me up the wall. It makes expressing just one of the two things harder than expressing both, leading to contortions when you want just one, like this use of :.
I use this for setting overridable defaults (this should hopefully actually be in the article I haven't read yet)
: ${DEBUG:=false}
debug is not only false, but garanteed to be set to something so that elsewhere the places that use it don't need extra syntax and checking in case it's empty, and yet you can just set it from the parent environment to override without touching the script or adding a commandline args parser.
And do me, reading this is almost as easy on the brain as just plain DEBUG=true.
Even if you aren't familiar with the extra syntax, like you're someone else in the future who needs to look at it, the two important words pop out, and probably don't mean NOT because whatever those extra bits mean, there's no !. So you get the idea well enough & cruise on.
...[edit] yep it's in the article.
but one thing isn't, exactly
In other words, maybe you should have figured out some other way to write the whole construct, but IF you want to write the if/else this way maybe for just readability or organization, and you want the else-block to only hinge on the initial condition and not also on whatever the then-block might do, then you need a safety-true at the end of the then-block.
$1 might also just be the first parameter for a function call, so you might not need that parameter to have a specific/readable name if the function is not very complex or long. I have plenty in my dot-files that are just one-line functions that don't need to be three-line functions just to give the single parameter it accepts a name.
- it creates the file if it does not exist, not merely truncate. as a tutorial kind of blog post this incomplete description matters IMO.
- it would work the same without the colon (similar for default variable assignment examples). we generally strive not to have "extra" things, like useless use of cat.
- educationally it's useful to demonstrate that redirection, like parameter expansion, works before the command executes (the null command in this case), but the article doesn't explain that at all!
otherwise i <3 this article. some uses of colon i had never thought of or seen before. like file truncation, not sure i'd use them but it was cool to see them.
life is way too short to deal with this nightmare of a language and its 50000 footguns for anything longer than a 2 line script, especially in the age of LLMs. Just write a python/TS/any real language script instead. Bash is great for the command line, it should be limited to use there.
What other language is it as easy, fast, and painless to work with file contents? I can toss data down and lift it back up with some <> symbols and a path, none of Python's "errrm, how would you like to open that file " handholding. And why the hell would I want to go learn TypeScript!?!?
Sometimes I feel like the people on HN repeating the trope "uhhh if you need ____ go learn a real language!" are just bad at writing shell scripts.
> Though.. what if I told you the above four lines could be replaced by just... one?
I'd reject the pull request. Bash is already bad as programming language (the goodness of language for long code is inversely proportional to how nice it is for shell one-liners), this is just turning "bad" into "line noise"
If your bash script takes more than one screen, rewrite it in Python, hell, rewrite it in Perl, even that's better
As a go-to idiom for a writability test, it gives me pause. If the file didn't exist, we created a zero-length one. That might be okay if we are going to write to it anyway as the next action.
If we are testing because we intend to overwrite it, why not just "> result.json" (which is by itself an idiom for truncating a file to zero length).
When would we every do this? Maybe before some command which takes the file name as a destination file argument rather than using output redirection, and which performs a lengthy computation before trying to open the file for writing. We can catch the permission error early.
I don't think I've ever coded such a test; normally you just do the operation that writes to the file and let that fail.
In POSIX C, there is a function access() for doing these kinds of tests. But it has a special purpose: it is meant to be used by a setuid root process to perform a permission test as if it were the real user/group (the one which elevated privilege to root). I.e. it's not can we do this operation, but should we do this operation (would we still be allowed, if we dropped privileges back to the original user).
This is an excellent article that helps people decide
against writing shell scripts. I abandoned doing so
shortly after I switched to linux. Since then I was
also using ruby. I still do not understand why people
would prefer shell scripts over ruby (or python). On
systems without ruby or python, one may see a benefit
in using shell scripts; other than that I fail to see
why shell scripts are necessary.
Shell scripts simply suck for many reason. They are
ugly, verbose, convoluted, outright stupid too such
as argument passing into functions. Then there is
straight up retarded stuff such as case/esac. Whoever
came up with that was clearly an incompetent language
designer.
I really hate bash because of its unreadable syntax, and this does not help it in any way.
We have some large bash scripts in my company, ~10,000 LOC spread across multiple files, all sourcing each other and what not. It is truly hard to read bash, which means it is truly hard to maintain bash, which means that when the one person knowing the bash scripts in your company goes away, you're in for some "fun".
My point is, these quirks are not useful, except for some bash enthusiasts.
Its not "unreadable" syntax, it's terse and unfamiliar. There are many languages with terse and unfamiliar syntax to me that I struggle to read, but only because I'm unfamiliar. In fact, most programming languages have unreadable syntax at first, save for maybe...AppleScript? Maybe Scratch. Even Python's famous readability isn't guaranteed, some of its functional programming facilities are just as arcane and unreadable as *sh.
I spend about 50% of time working time in the shell. I didn't find anything in TFA unreadable.
I've read through all of the examples in the article & they all seem to serve to sole purpose of turning readable multiple line code into one-liners.
One-liners are a cool little artifact of early shell culture & are sometimes still useful today if they're short to avoid the readability problems of `/` when copy pasting a quick shell command to run, but they have no place in scripts.
None of this seems useful to me.
> if you are like me and prefer less typing (gotta go fast)
$ ./script.ps1 Dave
Hello, Dave!
$ ./script.ps1 -name Dave
Hello, Dave!
$ ./script.ps1
cmdlet script.ps1 at command pipeline position 1
Supply values for the following parameters:
name: <cursor here>
Or non interactively:
$ pwsh -nonint ./script.ps1
script.ps1: Cannot process command because of one or more missing mandatory parameters: name.
I usually skip the get option builtin, and use : as...
while : ; do
case "$1" in
"") break;;
-f|-foo) shift; whatever;;
*) usage; exit 1;;
esac
done
For this... instead
if something; then
true
else
echo ERROR
exit 1
fi
Using : would be too much here.
For anything else including json etc. I usually go to duckdb. Awesome support, single file install, readable, easy to maintain.
Powershell on Linux or Unix? Just another huge dependency if you manage 1000s of machines, and good luck finding a Linux gal/guy wanting or able to touch pwsh without chemical grade gloves.
> If the pipeline does not begin with the "!" reserved word, the exit status shall be the exit status of the last command specified in the pipeline. Otherwise, the exit status shall be the logical NOT of the exit status of the last command
Why take a perfectly readable if-statement and turn it into something, 99.9% of people would need to lookup. Concise != better. You can make it one line with:
the people writing it are doing it for themselves probably. i wouldn’t expect it to survive a code review. the necessity of using esoteric bash features or syntax is a pretty good smell that you should be using something else imo.
Off-topic, but I am reminded of Larry's First and Second Laws of Language Redesign (which Larry Wall discovered/stated when he designed Perl 6, which is now Raku):
1. Everyone wants the colon.
2. Larry gets the colon.
there are some early unix tapes floating around, and in those early shells, i'm fairly certain the colon was one of only two special-cased code paths after the command line was parsed. does anyone recall more specifically?
56 comments
[ 1.5 ms ] story [ 36.7 ms ] threadMany of the others (like truncating files) are probably more clearly written with dedicated commands, but may come in useful if you are going to extreme lengths to avoid dependencies outside of the shell.
You are very much correct and I 100% agree with you, I have updated the first example to include a snippet where a proper env-var is used to show of the automatic diagnostic.
Thanks for your feedback, much much appreciated!
> Why use the null-command when I could do VAR=${VAR:-default-value}?
and points out it's one less thing to typo, but that assumes the name is the same; I like e.g.
: ${DEBUG:=false}
debug is not only false, but garanteed to be set to something so that elsewhere the places that use it don't need extra syntax and checking in case it's empty, and yet you can just set it from the parent environment to override without touching the script or adding a commandline args parser.
And do me, reading this is almost as easy on the brain as just plain DEBUG=true.
Even if you aren't familiar with the extra syntax, like you're someone else in the future who needs to look at it, the two important words pop out, and probably don't mean NOT because whatever those extra bits mean, there's no !. So you get the idea well enough & cruise on.
...[edit] yep it's in the article. but one thing isn't, exactly
In other words, maybe you should have figured out some other way to write the whole construct, but IF you want to write the if/else this way maybe for just readability or organization, and you want the else-block to only hinge on the initial condition and not also on whatever the then-block might do, then you need a safety-true at the end of the then-block.- it creates the file if it does not exist, not merely truncate. as a tutorial kind of blog post this incomplete description matters IMO.
- it would work the same without the colon (similar for default variable assignment examples). we generally strive not to have "extra" things, like useless use of cat.
- educationally it's useful to demonstrate that redirection, like parameter expansion, works before the command executes (the null command in this case), but the article doesn't explain that at all!
otherwise i <3 this article. some uses of colon i had never thought of or seen before. like file truncation, not sure i'd use them but it was cool to see them.
Sometimes I feel like the people on HN repeating the trope "uhhh if you need ____ go learn a real language!" are just bad at writing shell scripts.
I'd reject the pull request. Bash is already bad as programming language (the goodness of language for long code is inversely proportional to how nice it is for shell one-liners), this is just turning "bad" into "line noise"
If your bash script takes more than one screen, rewrite it in Python, hell, rewrite it in Perl, even that's better
The subshell execution parentheses and the colon are superfluous here, just:
Redirections do not require a colon command to hang off of, and there is no need to fork a subshell to execute such a command.> ( : >> result.json ) && echo YES # is result.json writable?
As a go-to idiom for a writability test, it gives me pause. If the file didn't exist, we created a zero-length one. That might be okay if we are going to write to it anyway as the next action.
If we are testing because we intend to overwrite it, why not just "> result.json" (which is by itself an idiom for truncating a file to zero length).
When would we every do this? Maybe before some command which takes the file name as a destination file argument rather than using output redirection, and which performs a lengthy computation before trying to open the file for writing. We can catch the permission error early.
I don't think I've ever coded such a test; normally you just do the operation that writes to the file and let that fail.
In POSIX C, there is a function access() for doing these kinds of tests. But it has a special purpose: it is meant to be used by a setuid root process to perform a permission test as if it were the real user/group (the one which elevated privilege to root). I.e. it's not can we do this operation, but should we do this operation (would we still be allowed, if we dropped privileges back to the original user).
Shell scripts simply suck for many reason. They are ugly, verbose, convoluted, outright stupid too such as argument passing into functions. Then there is straight up retarded stuff such as case/esac. Whoever came up with that was clearly an incompetent language designer.
We have some large bash scripts in my company, ~10,000 LOC spread across multiple files, all sourcing each other and what not. It is truly hard to read bash, which means it is truly hard to maintain bash, which means that when the one person knowing the bash scripts in your company goes away, you're in for some "fun".
My point is, these quirks are not useful, except for some bash enthusiasts.
I spend about 50% of time working time in the shell. I didn't find anything in TFA unreadable.
One-liners are a cool little artifact of early shell culture & are sometimes still useful today if they're short to avoid the readability problems of `/` when copy pasting a quick shell command to run, but they have no place in scripts.
None of this seems useful to me.
> if you are like me and prefer less typing (gotta go fast)
Yeah, no.
Also, I'll never use it.
Because a language feature that needs marketing is against readability, among those in my target audience who have not yet read the marketing.
I need my shell scripts to be long enough to explain to my audience exactly what they are doing.
while : ; do case "$1" in "") break;; -f|-foo) shift; whatever;; *) usage; exit 1;; esac done
For this... instead
Using : would be too much here.For anything else including json etc. I usually go to duckdb. Awesome support, single file install, readable, easy to maintain.
Powershell on Linux or Unix? Just another huge dependency if you manage 1000s of machines, and good luck finding a Linux gal/guy wanting or able to touch pwsh without chemical grade gloves.
However, the only one I already knew...
I used to do that until I learned of It's in the POSIX standard so it's not just a bashism: https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V...> If the pipeline does not begin with the "!" reserved word, the exit status shall be the exit status of the last command specified in the pipeline. Otherwise, the exit status shall be the logical NOT of the exit status of the last command
I have an alias[1] for that which I call a quick interactive rebase:
[1]: https://github.com/fphilipe/dotfiles/blob/94f2ff70bade070694...different strokes of course.
Some of the examples here are interesting, but they show parameter substitution more than colon itself: https://tldp.org/LDP/abs/html/parameter-substitution.html
In small scopes, I tend to inline the `:?` validation inside the arg of the command. `echo "${1:? first param required}"`
Another usecase is to use colon in the body of a while loop, while doing work in the condition of the loop.
Gives you the "do X while it succeeds. stop when it returns non-0" semantics.I've also written about this and other bash tricks over the years in https://github.com/kidd/scripting-field-guide/blob/master/bo.... You might like them :)
Btw, can the sequence :? be called "reverse Elvis" ?