The ultimately sad part was the professor in a Sun OS machine.
In a corner with no where to go, giving demerits because his bash was older than he realized.
Reminds me of my college professor that claimed you don’t have to close HTML tags (some you absolutely do) and I proved that you do. Not all of them, but most of them. (Netscape Navigator Days)
> When I was a young, green, university student, I was forced to use test(1) as the only true way to do testing in shell scripting. […] Yeah, I was also forced to not use semicolons as they were evil (according to my professor, any comment unneeded!).
The author’s professor clearly went gone overboard, but doesn’t this entire anecdote demonstrate the value of teaching it this way? Having green students call the `test` binary provides more insight into how UNIX operates, and gets them into that mindset.
[[ ... ]] supports regex comparisons and lets you combine multiple conditions in a single bracket group using && and || instead of remembering to use -a / -o.
I usually default to [ ... ] unless I need features that double brackets provide.
I personally use ((...)) for arithmetic tests and [[...]] for all other tests as I just target new versions of BASH and don't care much about POSIX compatibility.
Use ((...)) for arithmetic tests and [[...]] for other tests. [...] is for POSIX compatibility and not as useful as [[...]] though I don't remember the specifics.
So if you really want to troll someone, you can put them in quotes.
The ultimately sad part was the professor in a Sun OS machine.
In a corner with no where to go, giving demerits because his bash was older than he realized.
Reminds me of my college professor that claimed you don’t have to close HTML tags (some you absolutely do) and I proved that you do. Not all of them, but most of them. (Netscape Navigator Days)
It doesn’t have anything to do with bash (though modern bash may use a built in for `[`). He don’t have the `[` program (usually linked to `test`).
Here's Greg's Wiki about the difference between [, [[ and test
https://mywiki.wooledge.org/BashFAQ/031
> When I was a young, green, university student, I was forced to use test(1) as the only true way to do testing in shell scripting. […] Yeah, I was also forced to not use semicolons as they were evil (according to my professor, any comment unneeded!).
The author’s professor clearly went gone overboard, but doesn’t this entire anecdote demonstrate the value of teaching it this way? Having green students call the `test` binary provides more insight into how UNIX operates, and gets them into that mindset.
Hmm. What if we replaced the whole of bash with the contents of /bin?
Nowadays [ is a builtin. The subprocess for a simple branch would be excessive overhead.
It is indeed a builtin, but `/bin/[` still exists for compatibility reasons!
The same is true for the `test` command:Now do [ ... ] and [[ ... ]]
I'm still not sure when to use one or the other. I use double brackets by default until something doesn't work.
[[ ... ]] supports regex comparisons and lets you combine multiple conditions in a single bracket group using && and || instead of remembering to use -a / -o.
I usually default to [ ... ] unless I need features that double brackets provide.
[[...]] is non-portable and has an extremely quirky corner case with variable expansion in arithmetic contexts, what's not to love?
I'm intrigued - any info on that?
I personally use ((...)) for arithmetic tests and [[...]] for all other tests as I just target new versions of BASH and don't care much about POSIX compatibility.
Use ((...)) for arithmetic tests and [[...]] for other tests. [...] is for POSIX compatibility and not as useful as [[...]] though I don't remember the specifics.
Double brackets are less portable. For example musl linux does not come with bash by default, and your script fails.
When unsure, use shellcheck.
You mean shellcheck will detect when single brackets won't be enough? I've also just defaulted to double because I never really looked into it
[[ is built in, so "test[" as an /usr/bin artifact never exists? (What to call that proposed program, test2, or test[ ?)