Reminds me of my rather memorable introduction to special characters invoking functions, seeing this dastardly little quip in the email signature of someone in a mailing list (circa '95 or so).
:(){:|:&};:
My curiosity piqued, I pasted it into the shell on my terminal in a pure example of FAFO. The poor little Sparc 5 I was using ground to a halt over the course of about ten seconds. The reboot was as hard as the lesson. xD
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)
In college I took a database class, it was pretty basic overall as I had been playing with MySQL for a few years at that point. On the final exam I got a 90/100. The test was 10 questions that just had you write SQL to answer the question. I got all the queries 100% correct... except... I didn't put a ";" after each query. On a written test. I'm still a little bitter about that.
> 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 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 using a UNIX mindset. They can discover the syntactic shortcuts later.
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.
[[ ... ]] 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.
Use ((...)) for arithmetic tests and [[...]] for other tests. [...] is for POSIX compatibility and not as useful as [[...]] though I don't remember the specifics.
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)
Precisely because those older systems didn’t link to it!
So my comment still stands.
The author’s professor clearly went 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 using a UNIX mindset. They can discover the syntactic shortcuts later.
I do think it makes sense to have beginners use `sh` instead of `bash`.
https://mywiki.wooledge.org/BashFAQ/031
I'm still not sure when to use one or the other. I use double brackets by default until something doesn't work.
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.
I usually default to [ ... ] unless I need features that double brackets provide.
When unsure, use shellcheck.